JP3824677B2 - Magneto-optical recording medium - Google Patents

Description

【００５３】
補助磁性膜４ｂは、遷移金属元素を含有し、かつ垂直磁気異方性が小さい磁性体をもって構成される。具体例としては、
▲１▼〔Ｐｔ，Ａｌ，Ａｇ，Ａｕ，Ｃｕ，Ｒｈ〕などの貴金属元素群から選択された少なくとも１種類の元素と、〔Ｆｅ，Ｃｏ，Ｎｉ〕などの遷移金属元素群から選択された少なくとも１種類の元素との合金薄膜、
▲２▼例えばＧｄＦｅＣｏ合金、ＧｄＴｂＦｅＣｏ合金、ＧｄＤｙＦｅＣｏ合金、ＮｄＦｅＣｏ合金など、ＧｄやＮｄを含有することにより、垂直磁気異方性を低下させた希土類−遷移金属系合金、
▲３▼酸素や窒素を通常より多量に（例えば５原子％以上）含有することにより、垂直磁気異方性を低下させた希土類−遷移金属系合金、
▲４▼〔Ｆｅ，Ｃｏ，Ｎｉ〕などの遷移金属単体、あるいはこれらを多量に含有する合金を５〜３０Åと数原子層の厚さで積層した膜、
などを挙げることができる。
【００５４】
これらの補助磁性膜４ｂは、組成によっては垂直磁気異方性エネルギが形状異方性と同じか若しくはそれより低くなり、外部磁界が印加される以前において、磁化を面内方向（補助磁性膜４ｂの膜面と平行な方向）に向けることができる。このように調整された補助磁性膜４ｂは、キュリー温度近傍まで昇温され、外部磁界が印加されると、磁化の方向が面内方向より立ち上がって外部磁界方向の磁気モーメント成分を生じ、これに接して積層されている非晶質垂直磁化膜４ａの遷移金属磁気モーメントに交換結合力を及ぼす。したがって、非晶質垂直磁化膜４ａと補助磁性膜４ｂとを積層してなる第１記録層は、外部磁界に対する光変調記録信号の搬送波及び雑音レベルの変化が、図９（ｂ）に示すように、２つのピークをもつようになる。
【００５５】
第２磁性層６は、前記第１磁性層４とは異なる磁界領域に少なくとも１以上の記録状態が存在する光磁気記録膜で構成される。したがって、前記第１磁性層４と同種の非晶質垂直磁化膜及び補助磁性膜からなり、前記第１磁性層４とは異なる磁界領域に２つの記録状態が存在するものを用いることもできるし、前記第１磁性層４とは異なる構成を有し、図９（ｃ）に示すように、前記第１磁性層４とは異なる磁界領域に１つの記録状態が存在するものを用いることもできる。後者に属する第２磁性層６としては、▲１▼室温から記録、消去時の最高到達温度までの温度範囲で遷移金属副格子磁化が優勢な希土類−遷移金属系の非晶質垂直磁化膜からなるもの、▲２▼前記と同様の温度範囲で、希土類副格子磁化が優勢な希土類−遷移金属系の非晶質垂直磁化膜からなるもの、▲３▼室温からキュリー温度までの間に補償温度が存在する希土類−遷移金属系の非晶質垂直磁化膜からなるものなどを挙げることができる。具体的には、下記の一般式で表されるものが特に好ましい。なお、この第２磁性層６の膜厚は、１００〜５００Åの範囲に形成することが好ましい。
【００５６】

【００５７】
前記の各膜体３〜８は、例えばスパッタリングや真空蒸着などの真空成膜法によって、透明基板１のプリフォーマットパターン形成面に順次積層される。これらの各膜体３〜８は、多値記録された光情報記録媒体から信号を読み出したとき、各記録レベルに応じた再生出力レベル（カー回転角の大きさ）の差が、相互にできるだけ均等になるように膜厚及び光学定数が選択される。その際の選択によっては、第２及び第３のエンハンス膜５，７及び／又は反射膜８は、省略することもできる。また、第１磁性層４と第２磁性層６とは、積層位置が相互に入れ替わっても良い。各磁性層の積層位置を入れ替えると、記録時の外部磁界の大きさや照射されるレーザパワーの大きさに対応する各記録状態のカー回転角の大きさが変化するが、信号の多値記録は可能であり、光磁気記録媒体としての特性や効果については何ら変化を有しない。また、磁性層を３層以上の多層に積層することによって、より高次の多値記録を行うことも可能であり、それに応じて各膜の組成を適宜変更することもできる。
【００５８】
以下に、本例に属する光磁気記録媒体の実施例を例示する。
【００５９】
〈第１実施例〉
図１０に示すように、本例の光磁気記録媒体は、透明基板１のプリフォーマットパターン形成面２に、膜厚が１００ｎｍのＳｉＮ膜と、膜厚が１５ｎｍのＴｂ₁₉Ｆｅ₆₂Ｃｏ₁₀Ｃｒ₉ 膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が２０ｎｍのＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜と、膜厚が５ｎｍのＰｔ₈₀Ｃｏ₂₀膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が７０ｎｍのＡｌ膜とを順次積層し、これらの各膜を紫外線硬化性樹脂膜で覆っている。
【００６０】
膜厚が１００ｎｍのＳｉＮ膜は第１誘電体層３、膜厚が１０ｎｍの２つのＳｉＮ膜は、それぞれ第２及び第３の誘電体層５，７を構成している。Ｔｂ₁₉Ｆｅ₆₂Ｃｏ₁₀膜は、単層で第１磁性層４を構成しており、特定の磁界領域に１つの記録状態が存在する。互いに直接積層されたＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜とＰｔ₈₀Ｃｏ₂₀膜は、第２磁性層６を構成しており、第１磁性層４とは異なる磁界領域に２つの記録状態が存在する。さらに、Ａｌ膜は反射膜８を構成し、紫外線硬化性樹脂膜は保護膜９を構成している。
【００６１】
〈第２実施例〉
図１１に示すように、本例の光磁気記録媒体は、透明基板１のプリフォーマットパターン形成面２に、膜厚が１００ｎｍのＳｉＮ膜と、膜厚が１５ｎｍのＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜と、膜厚が２ｎｍのＧｄ₁₈Ｆｅ₆₇Ｃｏ₁₅膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が２０ｎｍのＴｂ₁₉Ｆｅ₆₂Ｃｏ₁₀Ｃｒ₉膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が７０ｎｍのＡｌ膜とを順次積層し、これらの各膜を紫外線硬化性樹脂膜で覆っている。
【００６２】
互いに直接積層されたＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜とＧｄ₁₈Ｆｅ₆₇Ｃｏ₁₅膜は、第１磁性層４を構成しており、異なる磁界領域に２つの記録状態が存在する。Ｔｂ₁₉Ｆｅ₆₂Ｃｏ₁₀膜は、単層で第２磁性層６を構成しており、第１磁性層４とは異なる磁界領域に１つの記録状態が存在する。本例の光磁気記録媒体は、第１実施例に係る光磁気記録媒体とは異なり、基板１に近い側、すなわち記録再生用レーザビームの入射側に設けられる第１磁性層４を、２つの磁性膜の積層体から構成したことを特徴とする。そこで、第２磁性層６へのレーザビームの入射量を減らさないことを目的として、第１磁性層４を構成する補助磁性膜としてレーザビームの吸収率が低いＧｄＦｅＣｏ膜を用いると共に、その膜厚を２ｎｍと極薄にした。その他の各部分については、第１実施例と同じであるので、対応する部分に同一の符号を表示して説明を省略する。
【００６３】
〈第３実施例〉
図１２に示すように、本例の光磁気記録媒体は、透明基板１のプリフォーマットパターン形成面２に、膜厚が１００ｎｍのＳｉＮ膜と、膜厚が１５ｎｍのＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜と、膜厚が７ｎｍの（Ｔｂ₃₂Ｆｅ₅₆Ｃｏ₁₂）₉₂Ｏ₈ 膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が２０ｎｍのＴｂ₁₉Ｆｅ₆₂Ｃｏ₁₀Ｃｒ₉膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が７０ｎｍのＡｌ膜とを順次積層し、これらの各膜を紫外線硬化性樹脂膜で覆っている。
【００６４】
互いに直接積層されたＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜と（Ｔｂ₃₂Ｆｅ₅₆Ｃｏ₁₂）₉₂Ｏ₈ 膜は、第１磁性層４を構成しており、異なる磁界領域に２つの記録状態が存在する。Ｔｂ₁₉Ｆｅ₆₂Ｃｏ₁₀膜は、単層で第２磁性層６を構成しており、第１磁性層４とは異なる磁界領域に１つの記録状態が存在する。本例の光磁気記録媒体は、第２磁性層６へのレーザビームの入射量を減らさないことを目的として、第１磁性層４を構成する補助磁性膜としてレーザビームの吸収率が低い（Ｔｂ₃₂Ｆｅ₅₆Ｃｏ₁₂）₉₂Ｏ₈ 膜を用いると共に、その膜厚を７ｎｍに調整した。その他の各部分については、第１実施例と同じであるので、対応する部分に同一の符号を表示して説明を省略する。
【００６５】
〈第４実施例〉
図１３に示すように、本例の光磁気記録媒体は、透明基板１のプリフォーマットパターン形成面２に、膜厚が１００ｎｍのＳｉＮ膜と、膜厚が１５ｎｍのＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜と、膜厚が２ｎｍのＧｄ₃₀Ｆｅ₄₈Ｃｏ₂₂膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が２０ｎｍのＴｂ₃₄Ｆｅ₅₂Ｃｏ₁₄膜と、膜厚が５ｎｍのＰｔ₉₄Ｃｏ ₆膜と、膜厚が１０ｎｍのＳｉＮ膜と、膜厚が７０ｎｍのＡｌ膜とを順次積層し、これらの各膜を紫外線硬化性樹脂膜で覆っている。
【００６６】
互いに直接積層されたＴｂ₃₂Ｆｅ₅₆Ｃｏ₁₂膜とＧｄ₃₀Ｆｅ₄₈Ｃｏ₂₂膜は、第１磁性層４を構成しており、異なる磁界領域に２つの記録状態が存在する。また、互いに直接積層されたＴｂ₃₄Ｆｅ₅₂Ｃｏ₁₄膜とＰｔ₉₄Ｃｏ ₆膜は、第２磁性層６を構成しており、第１磁性層４とは異なる磁界領域に２つの記録状態が存在する。本例の光磁気記録媒体は、第２磁性層６へのレーザビームの入射量を減らさないことを目的として、第１磁性層４を構成する補助磁性膜としてレーザビームの吸収率が低いＧｄＦｅＣｏ膜を用いると共に、その膜厚を２ｎｍに調整した。その他の各部分については、第１実施例と同じであるので、対応する部分に同一の符号を表示して説明を省略する。
【００６７】
〈第２構成例〉
本例に係る光磁気記録媒体は、前記第１構成例に例示したごとき多値記録用の光磁気記録媒体に、いわゆる磁気超解像を実現するための膜体を付加したことを特徴とする。
【００６８】
図１４はその一例を示す構成図であって、２つの磁性層を有する多値記録用の光磁気記録媒体に本発明を適用した場合を示している。この図から明らかなように、本例の光磁気記録媒体は、透明基板１上に、第１誘電体層１０１と、第１開孔部形成層１０２と、第１切断層１０３と、第１垂直磁化膜層１０４と、第１補助磁性層１０５と、第２誘電体層１０６と、第２開孔部形成層１０７と、第２切断層１０８と、第２垂直磁化膜層１０９と、第２補助磁性層１１０と、第３誘電体層１１１と、反射層１１２とから原則的に形成される。第１磁性層１２０は、第１垂直磁化膜層１０４と第１補助磁性層１０５との組合せによって構成され、第２磁性層１２１は、第２垂直磁化膜層１０９と第２補助磁性層１１０との組合せによって構成される。
【００６９】
第１開孔部形成層１０２と第１切断層１０３と第１磁性層１２０は、室温において互いに磁気的に交換結合する磁性膜をもって構成され、再生用レーザビームの入射方向に対して、この順に積層される。これらの磁性膜１０２，１０３，１２０は、第１開孔部形成層１０２のキュリー温度をＴｃ₁ 、その保磁力をＨｃ₁ 、第１切断層１０３のキュリー温度をＴｃ₂ 、その保磁力をＨｃ₂ 、第１磁性層１２０のキュリー温度をＴｃ₃ 、その保磁力をＨｃ₃ とし、室温をＴ₀ 、第１切断層１０３及び第１磁性層１２０が第１開孔部形成層１０２に及ぼす交換磁界をＨ_w 、再生時に印加する外部磁界（以下、再生磁界という）をＨ_r とすると下記の▲１▼〜▲４▼の条件を満たすように、キュリー温度及び保磁力が調整される。
▲１▼Ｔ₀ ＜Ｔｃ₂ ＜Ｔｃ₁ ，Ｔｃ₃
▲２▼Ｈｃ₁ ＋Ｈ_w ＜Ｈ_r
（但し、再生時に第１切断層１０３のキュリー温度Ｔｃ₂ またはその近傍まで昇温する領域において）
▲３▼Ｈｃ₃ ＞Ｈ_r
（但し、再生時に第１切断層１０３のキュリー温度Ｔｃ₂ またはその近傍まで昇温する領域において）
▲４▼Ｈｃ₁ ＜Ｈ_w
（但し、室温において）。
【００７０】
なお、第２開孔部形成層１０７と第２切断層１０８と第２記録層１２１についても、これと同様に構成される。
【００７１】
以下、このように構成された光磁気記録媒体からの信号の再生原理を、図１５に基づいて説明する。光磁気記録媒体には、図１５（ａ）に示すように、記録トラックに沿って、再生用光ビーム１３０のスポット径Ｄよりも小径の記録マーク１２０ａ，１２１ａが、再生用光ビーム１３０のスポット径Ｄよりも小さなピッチで記録されている。
【００７２】
光学ヘッド及び磁気ヘッドに対して光磁気記録媒体を相対的に駆動しつつ、光磁気記録媒体に再生用光ビーム１３０を照射すると、そのエネルギによって第１開孔部形成層１０２、第１切断層１０３、第１磁性層１２０、第２開孔部形成層１０７、第２切断層１０８、第２磁性層１２１が昇温されるが、矢印Ａの方向に光磁気記録媒体を駆動しつつ記録トラックに沿って再生用光ビーム１３０を照射すると、相対的に走行する再生用光ビーム１３０の照射部内の温度分布により、図１５（ｂ）に示すように、スポット１３１の後縁部分が最も高温になる。そこで、再生用光ビーム１３０の強度を、当該高温領域１３１ａの温度が第１及び第２の切断層１０３，１０８のキュリー温度Ｔｃ₂ 以上又はその近傍になるように調整すると、切断層１０３，１０８及び磁性層１２０，１２１が開孔部形成層１０２，１０７に及ぼす交換磁界Ｈ_w がゼロ若しくは非常に小さな値となり、開孔部形成層１０２，１０７と磁性層１２０，１２１との間の磁気的結合が断ち切られる。
【００７３】
この状態で、Ｈｃ₁ ＋Ｈ_w よりも大きな再生磁界Ｈ_r を各磁性膜に印加すると、図１５（ａ）に示すように開孔部形成層１０２，１０７の高温領域１３１ａに対応する部分の磁化が再生磁界方向に揃えられ、その領域における開孔部形成層１０２，１０７の記録マーク１２０ａ，１２１ａは消失する。一方、高温領域１３１ａ以外の部分では、交換磁界Ｈ_w は大きな値を維持しており、開孔部形成層１０２，１０７と磁性層１２０，１２１とは磁気的に結合されているので、開孔部形成層１０２，１０７に記録された記録マーク１２０ａ，１２１ａはそのまま保たれている。したがって、記録トラックに沿って再生用光ビーム１３０を操作したとき、高温領域１３１ａ中の記録マーク１２０ａ，１２１ａが信号の読出しに関してマスクされ、スポット１３１のうちの高温領域１３１ａを除く三日月形の部分のみがアパーチャとなって、記録マーク１２０ａ，１２１ａからの信号が読み出される。よって、磁区間ピッチがスポット径Ｄの１／２程度に調整された光磁気記録媒体からの信号の読み出しが可能になり、再生分解能が向上する。
【００７４】
なお、磁性層１２０，１２１の保磁力Ｈｃ₃ は、再生磁界Ｈ_r よりも大きく設定されているので、再生磁界Ｈ_r の印加によって磁性層１２０，１２１の記録マーク１２０ａ，１２１ａが消去されることはない。また、光磁気記録媒体の駆動に伴って再生用光ビーム１３０の照射部から外れた部分は、順次室温まで冷却され、切断層１０３，１０８の温度がＴｃ₂ 以下まで冷却された段階で、再度各磁性膜間に交換磁界Ｈ_w が復活する。よって、その交換結合力によって磁性層１２０，１２１の反転磁区が開孔部形成層１０２，１０７に転写されるので、信号の再生動作を繰り返しても、当初の記録状態が消失することはない。よって、図１５（ｃ）に示すように、読み出されたトータルの再生信号を各信号レベルに合致した複数のスライス信号にてスライスすることによって、多値記録された信号を高い分解能で再生することができる。
【００７５】
図１６に、磁気超解像方式による多値記録信号再生方法の他の例を示す。本例の再生方式は、図１５の方法とは異なり、光学ヘッドの上流側において開孔部形成層１０２，１０７に初期化磁界を印加し、高温部１３１ａにアパーチャを形成することを特徴とする。
【００７６】
複数の開孔部形成層を有する光磁気記録媒体については、各磁性層と開孔部形成層との間に作用する交換結合力を相互に異ならせたり、あるいは各開孔部形成層のキュリー温度を相互に異ならせることによって、各磁性層ごとに再生信号を読みだすことができる。すなわち、再生光照射時の開孔部は、再生光入射側に近い第１磁性層１２０の方が大きくなる。そこで、高温部１３１ａにアパーチャを形成する光磁気記録媒体においては、第１磁性層１２０と第１開孔部形成層１０２との間に作用する交換結合力を第２磁性層１２１と第２開孔部形成層１０７との間に作用する交換結合力よりも強くするか、あるいは第１開孔部形成層１０２のキュリー温度を第２開孔部形成層１０７のキュリー温度よりも低く設定し、かつ適当な２パワーの再生用レーザビームを選び、図１７に示すように、第２磁性層には開孔部ができないような低パワーの再生用レーザビームを光磁気記録媒体に照射することによって、第１磁性層１２０のみから信号を再生することができる。また、図１８に示すように、第１記録層の開孔部が再生スポットのほぼ全域を覆うような高パワーの再生用レーザビームを光磁気記録媒体に照射することによって、第２磁性層のみから信号を再生することができる。
【００７７】
再生スポットの低温部にアパーチャを形成する光磁気記録媒体においては、第１磁性層１２０と第１開孔部形成層１０２との間に作用する交換結合力を第２磁性層１２１と第２開孔部形成層１０７との間に作用する交換結合力よりも弱くするか、あるいは第１開孔部形成層１０２のキュリー温度を第２開孔部形成層１０７のキュリー温度よりも高く設定することによって、第１又は第２の磁性層から選択的に信号を再生することができる。
【００７８】
なお、磁気超解像方式の多値記録用光磁気記録媒体は、必ずしも図１４に示した全ての膜体を備える必要はなく、必要に応じて１ないし複数の膜体を省略することもできる。図１９に、第４構成例に含まれる種々の膜構成を表示する。表中のブランクは、当該膜体が省略されていることを示している。
【００７９】
なお、前記第１及び第２構成例においては、誘電体層としてＳｉＮ膜を用いたが、他の材料を用いることもできる。すなわち、誘電体層材料としては、第１及び第２磁性層の記録時の温度分布をなるべく等しくしてそれぞれに形成される磁区の大きさを揃えるため、非磁性で熱伝導率が高い材料が良い。これに好適な材料としては、〔Ｓｉ，Ａｌ，Ｔｉ，Ｚｒ，Ａｕ，Ｃｕ，Ｍｏ，Ｗ〕のグループから選択される金属元素、又はこれらから選択された少なくとも１種類の金属元素を主成分とする合金、又はこれらの酸化物もしくは窒化物を挙げることができ、その組成が化学量論的組成より金属元素に富む材料が特に好適である。各誘電体層の膜厚は、光学的な条件を満たすように適宜調整される。
【００８０】
また、前記第１及び第２構成例における各垂直磁化膜のキュリー温度は、それぞれの記録層に形成される磁区の大きさを揃えるため、互いに近似していることが必要であり、最大±５０℃以内に設定することが好ましい。
【００８１】
その他、前記第１及び第２構成例における各垂直磁化膜の組成は、成膜を容易にするため、同一組成とすることが好ましい。また、前記補助磁性膜としては、少なくとも室温付近にて面内磁化膜となる磁性薄膜を用いることが好ましい。さらに、前記補助磁性膜は、前記垂直磁化膜の片面のみならず、レーザビーム入射側又はその反対側若しくはその双方に設けることができる。
【００８２】
以下に、光磁気記録媒体に対する高密度記録方法及び微細な記録磁区が形成された高密度記録媒体からのエラーの少ない記録再生方法を列挙する。
【００８３】
（１）パルス再生
ａ．再生用レーザビームを周期的又はパルス状に照射する光磁気再生方式。
【００８４】
ｂ．前記ａ．の信号再生方式において、再生用レーザ光の発光タイミングを、プリピットあるいは光磁気信号などの媒体から再生された信号によりタイミングクロックを作製して同期を取る方式。
【００８５】
（２）パルス再生の波形等化
ｃ．前記ａ．の方式による再生信号波形をＤ₀（ｔ）としたとき、下記の数１で表される信号処理を行う方法。
【００８６】
【数１】

【００８７】
ｄ．前記ｃ．の方法で、ｎ＝０，±１，±２，ａ_n＝ａ_-n，−１＜ａ_n＜０なる信号処理を行う方法。
【００８８】
（３）磁界変調再生
ｅ．磁気超解像が可能な媒体に対して、印加する外部磁界の大きさ及び又は方向を変調して再生を行う方式。
【００８９】
ｆ．前記ａ．の方式において、再生用レーザ光の発光タイミングに同期して、印加する外部磁界の大きさ及び又は方向を変調する前記ｅ．の再生方式。
【００９０】
ｇ．再生光スポット内にレーザ進行方向ないしクロストラック方向に複数の記録ピットが存在し、それらの記録状態の各組合せにより発現する再生信号の各レベルが、各々確定された多段階にある記録再生方式。
【００９１】
（４）試し読み
ｈ．前記ａ．〜ｇ．の方式において、再生用レーザ光の波形（高パワー、低パワーの各値、高パワーと低パワーの時間の比率）及び再生時に印加する磁場などを変えて再生を行い、最もエラーの少ない組合せを選択する再生方式。
【００９２】
ｉ．前記ｈ．の再生方式において、予め再生試行用のテストパターンを媒体に記録しておく方式。
【００９３】
ｊ．前記ｈ．の方式でえられた最適再生条件を媒体に記録し、次回の再生からは、それを読み取って再生を行う方式。
【００９４】
次に、本発明に係る光磁気記録媒体のフォーマット構成について説明する。
【００９５】
〈フォーマット構成の第１例〉
図２０に、サンプルサーボ方式の光磁気記録媒体に形成されるプリフォーマットパターンの一例を示す。プリフォーマットパターン２は、記録トラック及び当該記録トラックを分割してなるデータ記録単位を画定するものであって、透明基板１の表面に凹凸の形で記録することもできるし、磁性層４，６等に光磁気信号として記録することもできる。
【００９６】
本例においては、記録トラック１１が多数のデータ記録単位１２に分割され、各データ記録単位１２が、ＩＤ領域１３と、サーボ領域１４と、データ領域１５とに分割されている。ＩＤ領域１３には、各データ記録単位１２の境界を示すマークや当該データ記録単位のアドレス、それに誤り検出符号などが形成される。サーボ領域１４には、図２１に示すように、記録又は再生用のレーザビームを記録トラック１１に沿って走査するためのトラッキングピット１６と、最適な記録再生を行うためのテスト領域１７と、信号の記録再生に必要な基準クロックを引き込むために必要な埋め込みクロックピット１８とが形成される。テスト領域１７には、必要に応じて、記録領域１４に記録される多値記録信号に含まれる各信号のスライスレベルを設定するためのテスト信号（レベル検出用ピット）１７ａ及び／又は多値記録信号のエッジを検出するタイミングの基準となるタイミング信号を生成するためのテスト信号（タイミング検出用ピット）１７ｂが記録される。また、データ領域１５には、多値記録信号が、光磁気記録信号として記録される。
【００９７】
なお、サーボ領域１４にトラッキングピット１６を備える構成に代えて、記録又は再生用のレーザビームを記録トラック１１に沿って案内する案内溝を、透明基板１に形成することもできる。
【００９８】
また、透明基板の表面に、例えば凹凸の形で形成されるプリピット（位相ピット）は、当該媒体に対応した多値記録にすることも可能である。プリピットの多値化は、プリピットの長さ、幅、深さの変調又はプリピット位置のトラック方向に垂直な方向への偏位量、あるいはこれらの組合せによって実現できる。
【００９９】
〈フォーマット構成の第２例〉
本例のフォーマット構成は、ユーザがアクセスして信号の記録、再生、消去等を行うユーザ領域以外の領域に、最適な記録条件を検出するためのテスト領域を設けたことを特徴とする。図２２は、ＣＡＶ（角速度一定）方式の光ディスクに応用した場合の実施例図であって、ユーザ領域２１を介して、ディスクの最内周部及び最外周部に、テスト領域２２が設けられている。なお、テスト領域２２は、ディスクの最内周部又は最外周部のいずれか一方にのみ設けることもできる。また、図２３は、ＺＣＡＶ（Zoned −ＣＡＶ）方式の光ディスクに応用した場合の実施例図であって、ゾーン境界部の近傍にテスト領域２２が設けられている。なお、ＺＣＡＶ方式の光ディスクにおいても、ＣＡＶ方式の光ディスクと同様に、ディスクの最内周部及び最外周部にテスト領域２２を設けることもできる。
【０１００】
なお、ユーザ領域内の各データ記録単位のフォーマット構成については、前記第１例で説明したと同じであるので、重複を避けるために説明を省略する。
【０１０１】
以下、本発明に係る光磁気記録媒体を用いた信号の多値記録方法について説明する。
【０１０２】
〈多値記録方法の第１例〉
本例の多値記録方法は、いわゆるトレリス符号化変調方式を用いて符号化した多値記録信号を記録することを特徴とする。光磁気記録媒体としては、第１構成例に係る光磁気記録媒体（図９〜図１３の光磁気記録媒体）を用いることができる。
【０１０３】
第１例と同様にして光磁気記録媒体を駆動し、光学ヘッド及び磁気ヘッドを所定のトラックに位置付けた後、４相直交変調トレリス符号に対応する４値記録を行うために、図２４に示す畳み込み符号器で符号化を行う。図２５（ａ）は、図２４の畳み込み符号器にデータを入力したときのＸ₁ ，Ｘ₂ の状態を示す。一方、前記したように、図９の光磁気記録媒体は、図２５（ｂ）に示すような外部磁界に対する信号特性をもっている。そこで、図２５（ａ）に示したＸ₁ ，Ｘ₂ の順に信号振幅が割り振られるようにＸ₁，Ｘ₂を用いて印加磁界強度をＨ₀ 〜Ｈ₃ の４値に強度変調すると共に、この強度変調された４値の外部磁界を、記録クロックに同期して光情報記録媒体に印加する。そして、外部磁界が所定の値に切り替わった後、光学ヘッドより光パルスを照射して、光パルス照射部の各記録層を、外部磁界によって磁化反転できる温度まで加熱する。これによって、各光パルスの照射部に、外部磁界の大きさに応じた磁化ドメインが形成される。なお、この場合、外部磁界を変調しつつ、一定強度のレーザビームを連続的に照射してもよい。
【０１０４】
図２６は、本実施例の記録再生系の構成例である。本実施例においては、再生光をＩ−Ｖ変換した後、アナログ波形等化器を通すことにより光学的な符号間干渉を除去して、そのアナログ信号をＡ／Ｄ変換した。その後、デジタルトランスバーサルフィルタで内外周特性差を吸収して４値を判定し、ビタビ復号器に供給して２値化した。再生クロックは、Ａ／Ｄ変換後の信号で生成した。
【０１０５】
〈多値記録方法の第２例〉
本例の多値記録方法は、外部磁界を記録信号に応じて４段階に変調すると共に、記録用レーザビームをパルス状に変調することを特徴とする。光磁気記録媒体としては、第１構成例に係る光磁気記録媒体（図９〜図１３の光磁気記録媒体）を用いる。
【０１０６】
まず、光磁気記録媒体をターンテーブル等の媒体駆動部に装着し、透明基板側に光学ヘッドを、保護膜側に磁気ヘッドを配置する。媒体駆動部を起動して光磁気記録媒体と光学ヘッド及び磁気ヘッドとを相対的に所定の線速度で駆動し、光学ヘッド及び磁気ヘッドを所定のトラックに位置付ける。
【０１０７】
しかる後に、図２７（ａ）に示すように、磁気ヘッドより記録信号に応じて印加磁界強度がＨ₀ 〜Ｈ₃ の４値に信号変調され、かつ記録クロックに同期された外部磁界を光情報記録媒体に印加する。そして、外部磁界が所定の値に切り替わった後、光学ヘッドより図２７（ｂ）に示す光パルスを照射して、光パルス照射部の各記録層を、外部磁界によって磁化反転できる温度まで加熱する。これによって、各光パルスの照射部に、外部磁界の大きさに応じた図２７（ｃ）の磁化ドメインが形成される。
【０１０８】
なお、図２７（ｃ）においては、４値に記録された各磁化ドメインの磁化状態が、夫々、右下がり斜線と左下がり斜線と縦線と白地とで識別されている。白地は、第３構成例の光磁気記録媒体を構成する各垂直磁化膜の磁化方向の組合せが図３１（ａ）の状態“０”であることを表わし、左下がり斜線は、図３１（ａ）の状態“１”であることを表わす。また、右下がり斜線は、図３１（ａ）の状態“２”であることを表わし、縦線は、図３１（ａ）の状態“３”であることを表わしている。
【０１０９】
磁界強度の信号変調は、図２８の方式及び図２９又は図３０の信号変調回路によって行うことができる。なお、図２９及び図３０の磁気ヘッド駆動回路としては、図３２に示した回路を用いることができる。すなわち、図２７（ｅ）のタイミングチャートに示された記録クロック▲１▼とデータ信号（Ｓｉｇ．１）▲２▼の論理積をとることにより、奇数デ−タ（Ｓｉｇ．２）▲３▼を生成する。また、記録クロック▲１▼を反転した信号とデータ信号▲２▼の論理積をとることにより、偶数デ−タ（Ｓｉｇ．３）▲４▼を生成する。奇数デ−タ▲３▼をシフトレジスタを用いて１／２クロック遅延させた信号と、元の奇数デ−タ▲３▼との論理和をとることにより、奇数データ信号の長さを２倍化した信号▲５▼を生成する。同様に、偶数デ−タ▲４▼から信号▲６▼を生成する。これらの信号▲５▼、▲６▼を、ゲインが異なる増幅器Ｇ₁ ，Ｇ₂ でそれぞれ増幅し、これを加算する。次いで、この加算信号を磁気ヘッド駆動回路で電圧電流変換することによって、磁気ヘッドより図２８（ｂ）に示す外部磁界を印加するようにしている。
【０１１０】
また、図３０の回路では、記録信号を偶数ビットと奇数ビットとに分離し、タイミング合わせやパルス長の調整などの波形処理を行った後、ゲインが同一の増幅器Ｇでそれぞれ増幅する。次いで、各増幅信号を別々の磁気ヘッド駆動回路で電圧電流変換し、複数の巻線をもった磁気ヘッドより図２８（ｂ）に示す外部磁界を印加するようにしている。
【０１１１】
なお、磁気ヘッドに代えて、例えば電磁コイルなどの他の磁界発生装置を用いることも勿論可能である。さらに、１本の巻線をもった２つの磁気ヘッドを近接して配置し、これらの各磁気ヘッドより図２８（ｂ）に示す外部磁界を印加することもできる。
【０１１２】
各外部磁界の大きさに応じた磁化ドメインの記録状態は、図３１に示す通りである。したがって、磁化ドメイン列から読みだされる再生信号は、図２７（ｄ）のようになる。この再生信号を各記録状態からの再生信号出力に応じて所定の値に設定された３つのスライスレベルでスライスすると、図２７（ｅ）のタイミングチャートに示すように、記録信号を復調できる。具体的には、スライスレベル１で図２７（ｄ）のアナログ再生信号を２値化すると、図２７（ｅ）のｓｉｇ．１が得られる。同様に、スライスレベル２からはｓｉｇ．２が得られ、スライスレベル３からはｓｉｇ．３が得られる。図２７（ｅ）の奇数データ信号▲５▼は、ｓｉｇ．２を反転した信号とｓｉｇ．３の信号との論理積をとった後、ｓｉｇ．１の信号との論理和をとり、さらにクロックと同期させるためにクロック信号▲１▼とｓｉｇ．３の論理積をとることによって得られる。そして、偶数データ信号▲６▼を１／２クロック遅延させた信号▲７▼と信号▲５▼との論理和をとることにより、データ信号を復調できる。図３３に、信号再生回路のブロック図を示す。
【０１１３】
以上の方式で４値記録を行うことにより、通常の２値記録媒体を用いてマークエッジ記録を行った場合と比較して、記録線密度を２倍にすることができる。図３４に、同じ最小記録ドメインサイズで同じ情報を記録した場合における２値記録のマークエッジ記録と４値記録の状態とを比較して示す。この図の通り、本発明の４値記録によると、２値記録のマークエッジ記録に比べて、線記録密度を２倍にすることができる。
【０１１４】
〈多値記録方法の第３例〉
本例の多値記録方法は、検出窓幅Ｔと同一か、あるいはその整数倍の一定周波数で磁気ヘッド（電磁コイル）を駆動して光磁気記録媒体に外部磁界を印加しつつ、レーザ照射のタイミングを変調することを特徴とする。図３５は本例の多値記録に適用されるレーザの照射タイミング変調回路のブロック図であり、図３６は回路各部で取り扱われる信号のタイミングチャートである。光磁気記録媒体としては、第１構成例に係る光磁気記録媒体（図９〜図１３の光磁気記録媒体）を用いた。
【０１１５】
本例の多値記録方法においては、外部磁界の変化に同期して、その１周期に１回記録レーザパルスを照射し、各記録層を充分保磁力が小さくなる温度まで加熱して、冷却時に第１記録層の磁化及び第２記録層の磁化の双方又は一方を選択的に反転させる。磁化を反転させる状態の区別は、記録レーザパルスを照射するタイミングをずらすことによって行う。すなわち、図３６に示すように、タイミングがずれた４個のパルス列ｐａｌｓｅ１，ｐａｌｓｅ２，ｐａｌｓｅ３，ｐａｌｓｅ４を生成し、記録信号Ｄａｔａから分離した偶数ビット、奇数ビットの信号と論理演算して、各記録状態に相当する記録レーザ駆動パルスを生成する。
【０１１６】
図３７に信号再生回路のブロック図を、図３８に信号再生方式を示す。磁化ドメイン列から読みだされる再生信号を所定の値に設定された３つのスライスレベルでスライスし、それによって得られる３つの２値化信号ｓｉｇ１，ｓｉｇ２，ｓｉｇ３から、第１例の場合と同様の手順で記録信号を再生できる。
【０１１７】
〈多値記録方法の第４例〉
本例の多値記録方法は、検出窓幅Ｔと同一か、あるいはその整数倍の一定周波数で磁気ヘッド（電磁コイル）を駆動して光磁気記録媒体に外部磁界を印加しつつ、照射されるレーザの強度を変調することを特徴とする。図３９に本例の多値記録に適用されるレーザ強度変調回路のブロック図を示し、図４０に回路各部で取り扱われる信号のタイミングチャートを示す。
【０１１８】
図４１に信号再生回路のブロック図を、図４２に信号再生方式を示す。磁化ドメイン列から読みだされる再生信号を所定の値に設定された３つのスライスレベルでスライスし、それによって得られる３つの２値化信号ｓｉｇ１，ｓｉｇ２，ｓｉｇ３から、第２例の場合と同様の手順で記録信号を再生できる。
【０１１９】
〈多値記録方法の第５例〉
本例の多値記録方法は、記録信号に応じて多段階に印加磁界強度が信号変調された外部磁界を光磁気記録媒体に印加しつつ、当該光磁気記録媒体の所望の記録トラックに記録信号に応じて多段階にレーザ強度が信号変調されたレーザビームを照射することによって、光磁気記録媒体に信号を多値記録することを特徴とする。光磁気記録媒体としては、第１構成例に係る光磁気記録媒体を適用できる。
【０１２０】
特定の磁化特性を有する光磁気記録媒体に特定の信号を記録する場合であっても、印加磁界強度Ｈと照射レーザ強度Ｐの組合せは、種々考えられる。例えば、図４３（ａ）の磁化特性を有する光磁気記録媒体に図４３（ｄ）の磁区列を記録する場合、図４３（ｂ）に示すように外部磁界Ｈを４段階に切り換えて、最も低レベルの外部磁界強度から順にＨ₀，Ｈ₁，Ｈ₂，Ｈ₃とすると共に、図４３（ｃ）に示すように照射レーザ強度Ｐを４段階に切り換えて、最も低レベルの照射レーザ強度から順にＰ₂，Ｐ₃，Ｐ₀，Ｐ₁とし、（Ｈ₀，Ｐ₀）の組合せを信号“０”に割当て、（Ｈ₁，Ｐ₁）の組合せを信号“１”に割当て、（Ｈ₂，Ｐ₂）の組合せを信号“２”に割当て、（Ｈ₃，Ｐ₃）の組合せを信号“３”に割当て、さらに印加磁界強度Ｈ及び照射レーザ強度Ｐを図４３（ｂ），（ｃ）のパターンで駆動すると、図４３（ｄ）の磁区列を記録できる。
【０１２１】
また、図４４（ｂ）に示すように外部磁界Ｈを４段階に切り換えて、最も低レベルの外部磁界強度から順に−Ｈ₁ ，−Ｈ₀ ，Ｈ₀ ，Ｈ₁ とすると共に、図４４（ｃ）に示すように照射レーザ強度Ｐを２段階に切り換えて、低レベルの照射レーザ強度をＰ₁、高レベルの照射レーザ強度をＰ₀とし、（−Ｈ₁，Ｐ₁）の組合せを信号“０”に割当て、（−Ｈ₀，Ｐ₀）の組合せを信号“１”に割当て、（Ｈ₀，Ｐ₀）の組合せを信号“２”に割当て、（Ｈ₁，Ｐ₁）の組合せを信号“３”に割当て、さらに印加磁界強度Ｈ及び照射レーザ強度Ｐを図４４（ｂ），（ｃ）のパターンで駆動しても、図４４（ｄ）に示すように、図４３（ｄ）と同じ磁区列を記録できる。
【０１２２】
また、図４５（ｂ）に示すように外部磁界Ｈを２段階に切り換えて、低レベルの外部磁界強度を−Ｈ₀ 、高レベルの外部磁界強度をＨ₀ とすると共に、図４５（ｃ）に示すように照射レーザ強度Ｐを２段階に切り換えて、低レベルの照射レーザ強度をＰ₁、高レベルの照射レーザ強度をＰ₀とし、（−Ｈ₀，Ｐ₁）の組合せを信号“０”に割当て、（−Ｈ₀，Ｐ₀）の組合せを信号“１”に割当て、（Ｈ₀，Ｐ₀）の組合せを信号“２”に割当て、（Ｈ₀，Ｐ₁）の組合せを信号“３”に割当て、さらに印加磁界強度Ｈ及び照射レーザ強度Ｐを図６３（ｂ），（ｃ）のパターンで駆動しても、図４５（ｄ）に示すように、図４３（ｄ）と同じ磁区列を記録できる。
【０１２３】
〈多値記録方法の第６例〉
本例の多値記録方法は、多値記録信号を光磁気記録媒体に信号順に記録するのではなく、多値記録信号を光磁気記録媒体に特定の磁化状態を記録する複数の磁界及び／又は照射レーザの組合せに分割し、各組合せごとに順次信号を記録することを特徴とする。磁界の変数としては、磁界の大きさ、変調振幅範囲、変調周波数、又はこれらの組合せを利用することができ、照射レーザの変数としては、レーザ強度、変調周波数、パルス幅、又はこれらの組合せを利用することができる。光磁気記録媒体としては、第１構成例に係る光磁気記録媒体を適用できる。
【０１２４】
図４６に示す磁化特性を有する光磁気記録媒体を例にとって、本例の多値記録方法を説明する。
【０１２５】
図４７はその第１例を示すものであって、まず第１回目の記録は、光学ヘッドを所望のトラックに位置付け、Ｈ₀ の磁場のもとで一定強度のレーザ光を照射し、トラック全体を状態“０”にする。次いで、光学ヘッドを第１回目の記録が行われたトラックに再度位置付け、Ｈ₁ の磁場のもとでデータ“１”に対応する位置でレーザ光をパルス照射し、状態“０”の中に状態“１”の記録磁区を形成する。３回目の記録は、光学ヘッドを第１回目及び第２回目の記録が行われたトラックに再度位置付け、Ｈ₂ の磁場のもとでデータ“２”に対応する位置でレーザ光をパルス照射し、状態“０”，“１”の中に状態“２”の記録磁区を形成する。この際、状態“２”の記録磁区が状態“１”の記録磁区上に形成されないように、予め信号を変調しておく。同様に、第４回目の記録においては、光学ヘッドを第１回目〜第３回目の記録が行われたトラックに再度位置付け、Ｈ₃ の磁場のもとでデータ“３”に対応する位置でレーザ光をパルス照射し、状態“０”，“１”，“２”の中に状態“３”の記録磁区を形成する。この方式によると、外部磁場を高速で４値切り換えする必要がないので、記録再生装置の負担を軽いものにすることができる。
【０１２６】
図４８は、本方式の信号記録の第２例を示すものであって、第１回目の記録は、光学ヘッドを所望のトラックに位置付けた後、印加する外部磁界をＨ₀とＨ₁の２値に切り換えつつ、データ“０”と“１”に対応する位置でレーザ光をパルス照射することによって行う。次いで、光学ヘッドを第１回目の記録が行われたトラックに再度位置付け、印加する外部磁界をＨ₂とＨ₃の２値に切り換えつつ、データ“２”と“３”に対応する位置でレーザ光をパルス照射することによって行う。これによって、４値記録が完了する。この方式によると、外部磁界をＨ₀からＨ₃までの大きな振幅で高速に切り換える必要がなく、Ｈ₀〜Ｈ₁及びＨ₂〜Ｈ₃の小さな振幅で切り換えれば良いので、やはり記録再生装置の負担を軽いものにすることができる。
【０１２７】
なお、前例においては、トラックごとに各記録を繰り返したが、ゾーンごと、あるいはディスク全体にわたって同様の記録方式を適用することもできる。
【０１２８】
また、Ｈ₂，Ｈ₃が夫々−Ｈ₁，−Ｈ₀に等しい場合には、例えば２重コイルヘッドにより、一方でＨ₀〜Ｈ₁間あるいはＨ₂〜Ｈ₃間の変調振幅に相当する磁場を発生させ、もう一方で、（Ｈ₀−Ｈ₁）／２の一定磁界をバイアスとして発生させ、その＋と−を切り換えて重畳することにより、Ｈ₀〜Ｈ₁間あるいはＨ₂〜Ｈ₃間に相当する変調磁界を印加することができる。
【０１２９】
〈多値記録方法の第７例〉
本例の多値記録方法は、多値の信号レベルを正確に判定するため、信号を弁別するスライスレベルを設定するためのテスト信号を、光磁気記録媒体に記録することを特徴とする。光磁気記録媒体としては、前出の図２０及び図２１に示すフォーマットを有するものが用いられる。
【０１３０】
すなわち、多値記録方法の第１例と同様にして光磁気記録媒体を駆動し、光学ヘッドを所望のアドレスがあるトラックに、また、磁気ヘッドを当該所望のトラックの近傍に位置付けた後、磁気ヘッドより記録データに応じて外部磁界を印加しつつ、光学ヘッドよりレーザビームを照射して、外部磁界に応じた多値信号を記録する。このとき、記録した多値信号を弁別するスライスレベルを設定するためのテスト信号を図２０のテスト領域１７に記録し、その信号を再生することによって、スライスレベルの設定が行えるようにした。
【０１３１】
前記テスト信号のデータパターンは、図２９に示すように、多値の信号レベルの全てを少なくとも１ヵ所ずつ持つようにした。その信号長は、必要に応じて任意に設定できるが、多値の信号レベルを正確に判定するため、再生用レーザビームのスポット径よりも長くすることが特に好ましい。
【０１３２】
尚、ここで言う「多値の信号レベル」とは、各磁区の磁化の状態で規定される信号レベル、例えば図８２又は図８３において状態“０”、“１”、“２”で示される相対信号出力と、複数の微小な磁区が連続する磁区パターンの合計の磁化状態にて規定される信号レベル、例えば図８２又は図８３において状態（“０”、“２”）、（“１”、“２”）、（“０”、“１”）で示される相対信号出力の両者を含む。また、「信号長」とは、図８２又は図８３の例にあっては、“０”、“１”、“２”の磁化状態を現出する磁区の長さを指し、図８２又は図８３の例にあっては、（“０”、“２”）、（“１”、“２”）、（“０”、“１”）の磁化状態を現出するその磁区パターンの連続する長さを指す。これを再生用レーザビームのスポット径よりも長くすることによって、各信号のスライスレベルを設定するためのテスト信号の各レベルにおいて、前後の信号レベルを光学的な干渉によるレベルシフトを生じない領域とすることができる。また、磁気超解像型の光磁気記録媒体を考慮するならば、テスト信号の各レベルの信号に、前後の信号レベルと光学的な干渉によるレベルシフトを生じさせない領域をもたせることがより好ましい。
【０１３３】
多値記録信号の再生に当っては、図５０に示すように、テスト信号の再生時に、多値信号レベルの１〜ｎのレベルを各々サンプルホールドし、信号レベルｋとｋ＋１のサンプルホールドレベルＶ_k とＶ_k+1 から信号レベルｋとｋ＋１を弁別するためのスライスレベル(Ｖ_k ＋Ｖ_k+1 )／２を生成する。
【０１３４】
なお、前記テスト信号は、前記データ記録単位の先頭部分に記録することもできるし、データ記録単位中に一定間隔ごとに設けることもできる。また、前記データ記録単位は、セクタ構造を有する媒体の場合にはセクタ全体でも良いし、クロックの同期をとるための信号に挾まれた領域でも良い。さらには、データの変復調のブロックであっても良いし、任意のバイト数ごとに挿入しても良い。
【０１３５】
〈多値記録方法の第８例〉
本例の多値記録方法は、多値記録信号のエッジを検出するタイミングを正確に判定するためのテスト信号を、光磁気記録媒体に記録することを特徴とする。光磁気記録媒体としては、同じく、前出の図２０及び図２１に示すフォーマットを有するものが用いられる。
【０１３６】
すなわち、多値記録方法の第１例と同様にして光磁気記録媒体を駆動し、光学ヘッドを所望のアドレスがあるトラックに、また磁気ヘッドを当該所望のトラックの近傍に位置付けた後、磁気ヘッドより記録データに応じて外部磁界を印加しつつ、光学ヘッドよりレーザビームを照射して、外部磁界に応じた多値信号を記録する。このとき、記録した多値信号のエッジを再生するタイミングの基準信号を生成するためのテスト信号を図２１のテスト領域１７に記録し、その信号を再生することによって、エッジ検出の基準タイミングの生成が行えるようにした。
【０１３７】
前記テスト信号のデータパターンは、図５１に示すように、多値の信号レベル間の全てのエッジを少なくとも１ヵ所ずつ持つようにした。その信号長は、必要に応じて任意に設定できるが、各多値レベルの長さの光学的な位相シフトを防止するため、再生用レーザビームのスポット径の１／２よりも長くすることが特に好ましい。また、磁気超解像型の光磁気記録媒体を考慮するならば、テスト信号の各エッジの信号に、前後のエッジの信号と光学的な干渉によるレベルシフトを生じさせない長さ以上のエッジ間隔を設定することがより好ましい。
【０１３８】
本例の場合も、「多値の信号レベル」とは、各磁区の磁化の状態で規定される信号レベル、例えば図８２又は図８３において状態“０”、“１”、“２”で示される相対信号出力と、複数の微小な磁区が連続する磁区パターンの合計の磁化状態にて規定される信号レベル、例えば図８２又は図８３において状態（“０”、“２”）、（“１”、“２”）、（“０”、“１”）で示される相対信号出力の両者を含む。また、「信号長」とは、図８２又は図８３の例にあっては、“０”、“１”、“２”の磁化状態を現出する磁区の長さを指し、図８２又は図８３の例にあっては、（“０”、“２”）、（“１”、“２”）、（“０”、“１”）の磁化状態を現出するその磁区パターンの連続する長さを指す。これを再生用レーザビームのスポット径の１／２よりも長くすることにより、多値記録信号のエッジを検出するタイミングの基準と成るタイミング信号を生成するためのテスト信号の各エッジの信号は、前後のエッジの信号レベルと光学的な干渉によるエッジシフトを生じない。
【０１３９】
多値記録信号の再生に当っては、テスト信号の再生時に、各区エッジを独立に検出し、エッジ検出信号の基準タイミングを生成する。データ信号再生時には、各区エッジを独立に検出し、図５２に示すように、テスト信号のエッジ検出タイミングを基準にして、各エッジ検出信号を合成する。
【０１４０】
なお、本例の場合にも、前記テスト信号は、前記データ記録単位の先頭部分に記録することもできるし、データ記録単位中に一定間隔ごとに設けることもできる。また、前記データ記録単位は、セクタ構造を有する媒体の場合にはセクタ全体でも良いし、クロックの同期をとるための信号に挾まれた領域でも良い。さらには、データの変復調のブロックであっても良いし、任意のバイト数ごとに挿入しても良い。
【０１４１】
〈多値記録方法の第９例〉
本例の多値記録方法は、多値の信号レベルを正確に判定するため、信号を弁別するスライスレベルを設定するためのテスト信号を光磁気記録媒体に記録すると共に、多値記録信号のエッジを検出するタイミングを正確に判定するためのテスト信号を光磁気記録媒体に記録することを特徴とする。光磁気記録媒体としては、前出の図２０及び図２１に示すフォーマットを有するものが用いられる。
【０１４２】
すなわち、多値記録方法の第１例と同様にして光磁気記録媒体を駆動し、光学ヘッドを所望のアドレスがあるトラックに、また、磁気ヘッドを当該所望のトラックの近傍に位置付けた後、磁気ヘッドより記録データに応じて外部磁界を印加しつつ、光学ヘッドよりレーザビームを照射して、外部磁界に応じた多値信号を記録する。このとき、記録した多値信号を弁別するスライスレベルを設定するためのテスト信号並びに記録した多値信号のエッジを再生するタイミングの基準信号を生成するためのテスト信号を図２１のテスト領域１７に記録し、その信号を再生することによって、スライスレベルの設定並びにエッジ検出の基準タイミングの生成が行えるようにした。
【０１４３】
前記各テスト信号のデータパターン並びに多値記録信号の再生方法については、前出の多値記録方法の第７例及び第８例と同じであるので、重複を避けるために説明を省略する。
【０１４４】
なお、本例の場合にも、前記テスト信号は、前記データ記録単位の先頭部分に記録することもできるし、データ記録単位中に一定間隔ごとに設けることもできる。また、前記データ記録単位は、セクタ構造を有する媒体の場合にはセクタ全体でも良いし、クロックの同期をとるための信号に挾まれた領域でも良い。さらには、データの変復調のブロックであっても良いし、任意のバイト数ごとに挿入しても良い。
【０１４５】
〈多値記録方法の第１０例〉
光磁気記録媒体にマークエッジ記録を行う一手段として、図５３に示すように、一定の周期で記録磁区を形成し、情報信号に応じて記録磁区のエッジ位置を記録磁区周期よりも十分に小さな範囲で２段階以上に段階的に変調させた。この方式を本発明の多値記録用光磁気記録媒体と組み合わせることにより、時間方向（トラック方向）と振幅方向の２次元多値記録が実現できる。なお、記録磁区の形成周期は、任意のエッジの信号とその前後のエッジの信号との光学的な干渉によるエッジシフトを生じない長さ以上の磁区長及び磁区間隔とすることがより好ましい。
【０１４６】
記録方法としては、記録用レーザビームと外部磁界とを同時に変調して記録する方式において、記録用レーザビームの照射強度、照射時間、照射タイミング、それに印加する外部磁界の強度あるいは切り替えのタイミングなどを記録情報に応じて変調する方法がとられる。
【０１４７】
図５４は、記録用レーザビームの照射パルス幅を、記録情報信号に応じて段階的に変調した例を示している。光−磁気変調記録においては、光磁気記録媒体が記録可能な温度に昇温された範囲が媒体冷却時に外部磁界に応じた磁区となるので、エッジの位置は記録用レーザビームの照射開始タイミングに大きく依存する。したがって、図５５のように、パルス幅一定で照射タイミングを記録情報信号に応じて段階的に変調することも可能である。さらには、熱的な履歴が残ることによるエッジシフトを防止するために、図５６に示すように、光照射パルスの前エッジを当該記録情報信号によって、また後エッジを次の記録情報信号に応じて段階的に変調しても良い。
【０１４８】
図５７は、記録用レーザビームの照射強度を、記録情報信号に応じて段階的に変調した例を示している。記録用レーザビームの照射強度を変調すると、記録磁区の大きさ、すなわち記録磁区の磁化状態及び長さが光強度に応じて変調されるので、光照射タイミングを変調する場合と同様に、エッジ位置を制御できる。また、光強度単独に限られず、光照射タイミング制御や光照射パルス幅制御と併用することも可能である。
【０１４９】
図５８は、外部磁界の強度を変調することにより、エッジ位置を制御した例を示している。光磁気記録媒体に印加される外部磁界強度を変化させると、記録磁区の大きさが変化するので、記録用レーザビームの照射強度等を変調する場合と同様に、エッジ位置を制御できる。もちろん、これと光強度制御や光照射タイミング制御、それに光照射パルス幅制御と併用することも可能である。
【０１５０】
図５９は、外部磁界の印加タイミングを変調することにより、エッジ位置を制御した例を示している。この場合、記録磁区のエッジ位置は、印加磁界の切り替え位置と対応するので、記録用レーザビームは、パルスのみならずＤＣ光でも良い。
【０１５１】
〈多値記録方法の第１１例〉
光−磁界変調記録においては、光強度と光パルス幅により基本的な磁区形状が決まる。図６０に示すように、記録用レーザビームの強度と記録パルス幅を同時に制御することにより、記録磁区長を一定に保ちつつ、記録磁区幅を変化させることができる。すなわち、これによって各記録レベルを微小に変化させることができるので、情報信号に対応してレベルの微小変調を行うことにより、記録の多値化が実現できる。前出の多値記録方法の第９例に示した２次元多値記録と復号すれば、記録磁区のエッジ位置、磁化状態に対応したレベル位置、及び磁区の幅に対応したレベル位置の３パラメータによる３次元多値記録が実現できる。
【０１５２】
〈多値記録方法の第１２例〉
本例の多値記録方法は、光学ヘッドのトラッキング制御方式として、サンプルサーボ方式を用いることを特徴とする。光磁気記録媒体としては、前出の図２１及び図６１（ａ）に示すフォーマットを有するものが用いられる。
【０１５３】
図２１及び図６１（ａ）に示すように、本例の光磁気記録媒体は、記録トラック１１が多数のデータ記録単位（セグメント）１２に分割されており、各データ記録単位（セグメント）１２には、サーボ領域１４とデータ記録領域１５とが設けられている。また、サーボ領域１４には、トラッキングピット１６と埋め込みピット１８とが予め設けられている。
【０１５４】
図６２は、かかるサンプルサーボ方式の光磁気記録媒体に好適な記録再生装置のブロック図であって、レーザから出射したレーザビームは、絞り込みレンズにより記録層上にスポットを形成する。一方、レーザスポットの近傍には、磁気コイル（磁気ヘッド）が配置されており、多値信号で強度変調された磁界を記録層に印加できるように構成されている。レーザから出射したレーザビームは、記録トラック１１に沿って照射され、レーザビームのトラッキングは、サーボ領域１４に設けられたトラッキングピット１６を検出することによって行われる。一方、信号の記録再生は、サーボ領域１４に設けられた埋め込みピット１８より検出される信号からＰＬＬ回路でチャネルクロックを生成し、このチャネルクロックでレーザ駆動回路、多値符号器、それに多値復号器を制御することによって行う。
【０１５５】
なお、光磁気ディスクにおいては、一般に基板の微小な複屈折率の変動により、再生信号のＤＣレベルが変動する。一方、サンプルサーボ方式の光磁気ディスクには、１トラック当たり１０００個以上のセグメントが存在し、その範囲内では、再生信号のＤＣレベルは一定であるとみなすことができる。そこで、各セグメントの一部、例えばテスト領域１７に信号が記録されない未記録領域を設けておくことによって、当該未記録領域の反射率を基準としてＤＣレベルの変動の補正を行うことができ、多値記録信号の識別を容易にすることができる。図６３に、図６２の記録再生装置に適用されるＤＣレベル補正回路の一例を示す。レベルクランプゲートは、前記未記録領域からの再生信号が検出された時点で、サンプルサーボ回路（Ｓ／Ｈ回路）をホールドするように制御する。
【０１５６】
〈多値記録方法の第１３例〉
本例の多値記録方法は、駆動装置の温度、環境温度、駆動装置の性能のばらつき、光磁気記録媒体の特性のばらつき等に関係なく、多値記録信号振幅（多値記録磁区幅）を一定に制御するためのテスト信号を、光磁気記録媒体のユーザ領域外に設けられたテスト領域に記録し、その再生信号を基準信号と比較して、記録レーザパワー及び／又は記録レーザパルス幅を制御することを特徴とする。光磁気記録媒体としては、前出の図２２及び図２３に示すフォーマットを有するものが用いられる。
【０１５７】
まず、光磁気記録媒体を記録再生装置に装着し、光学ヘッドをテスト領域２２中の所望のアドレスに位置付ける。また、磁気ヘッドを当該所望のトラックの近傍に位置付ける。しかる後に、光学ヘッド及び磁気ヘッドを駆動して、当該テスト領域に、当該光磁気記録媒体に記録しようとする多値記録信号を組み合わせた一定のテストパターンを記録する。次いで、当該テスト信号を再生して信号振幅を基準の信号振幅と比較し、光磁気記録媒体上の記録温度を一定に制御する。
【０１５８】
テスト信号の記録は、光磁気記録媒体を記録再生装置に装着した後であれば、必要に応じて適宜のタイミングで行うことができる。例えば、光磁気記録媒体を記録再生装置に装着した時点で行うこともできるし、記録再生装置の動作開始時点で行うこともできる。また、光磁気記録媒体に対する信号の記録動作の直前で行うこともできる。さらには、光磁気記録媒体を記録再生装置に装着した後、一定の時間間隔で行うこともできる。
【０１５９】
テストパターンの記録は、図６４（ａ）に示すように、多値記録信号の相隣接する２つの信号レベル間に近似した再生信号が得られるように、一定レベルの外部磁界をパルス状に印加しつつ、レーザパワーを連続的又は段階的に変化させて、単一の周波数で行う。本例では、各多値記録レベルについて、レーザパワーを０．１ｍＷずつ８段階に切り替えて、テストパターンの記録を行った。図６４（ｂ）にその再生信号波形を示す。そして、夫々の記録パワーの再生信号に対して信号の最小値、最大値をピークホールドし、信号振幅を求め、それらの信号振幅と基準の信号振幅との差が最も小さくなり、かつその差が一定の値以下になる条件を最適記録条件とする。最適記録条件が見つからない場合には、レーザパワーを上げてテスト記録を繰り返す。記録再生装置の最大パワーを超えても最適記録条件が見つからない場合には、エラーとして動作を終了する。
【０１６０】
図６５に、最適条件検出回路のブロック図を示す。基準の信号振幅は、媒体上のユーザ領域外でかつテスト領域外に予め記録された信号から求めることができる。また、媒体上に予め記録された基準信号振幅に関するデータを読み取って、記録再生装置で生成することもできる。さらには、記録再生装置に備えられたメモリに予め基準信号振幅に関するデータを記憶しておくこともできる。
【０１６１】
なお、前例においては、レーザパワーを変えることによってテストパターンを記録したが、記録パルス幅を変えてテストパターンを記録することもできるし、さらには、レーザパワーと記録パルス幅の両方を変えてテストパターンを記録することもできる。
【０１６２】
〈多値記録方法の第１４例〉
本例の多値記録方法は、駆動装置の温度、環境温度、駆動装置の性能のばらつき、光磁気記録媒体の特性のばらつき等に関係なく、多値記録信号振幅（多値記録磁区幅）を一定に制御するためのテスト信号を、光磁気記録媒体のユーザ領域外に設けられたテスト領域に記録し、その再生信号から各多値記録レベル間の振幅が等しくなるように記録外部磁界を制御することを特徴とする。光磁気記録媒体としては、前出の図２２及び図２３に示すフォーマットを有するものが用いられる。
【０１６３】
第１３例と同様に、まず、光磁気記録媒体を記録再生装置に装着し、光学ヘッドをテスト領域２２中の所望のアドレスに位置付ける。また、磁気ヘッドを当該所望のトラックの近傍に位置付ける。しかる後に、光学ヘッド及び磁気ヘッドを駆動して、当該テスト領域に、当該光磁気記録媒体に記録しようとする多値記録信号を組み合わせた一定のテストパターンを記録し、多値記録信号のレベル間の信号振幅が一定になるように外部磁界を制御する。
【０１６４】
テストパターンの記録は、図６６（ａ）に示すように、多値記録レベルの全てを含み、かつそのうちの２つの多値記録レベルを基準として、その他の各多値記録レベルの外部磁界を変化させるテストパターンを用いて行う。本例では、各多値記録信号レベルに対して、外部磁界を４段階に切り替えて、テストパターンの記録を行った。図６６（ｂ）にその再生信号波形を示す。そして、夫々の記録磁界の再生信号に対して信号レベルをサンプルホールドし、信号振幅を求める。また、得られた各多値信号レベルを比較して、信号レベル間隔が等しくなるような外部磁界の組合せを最適記録条件とする。図６７に、本例の記録再生方法に好適な最適条件検出回路のブロック図を示す。
【０１６５】
その他については、第１３例の記録再生方法と同じであるので、重複を避けるために説明を省略する。
【０１６６】
〈多値記録方法の第１５例〉
本例の多値記録方法は、光磁界変調記録を行う光磁気記録再生装置において、駆動装置の温度、環境温度、駆動装置ばらつき、光磁気記録媒体ばらつきに関係なく、多値記録信号の記録信号振幅（多値記録磁区幅）を一定に制御するために、レーザ光パワーおよびレーザ光パルス幅の少なくとも一方を変更しつつ、２種以上の光パルス周期でテスト信号の記録を行い、各々の信号レベルの平均値の差が一定の値になるように記録レーザパワーおよびレーザ光パルス幅の少なくとも一方を制御することを特徴とする。光磁気記録媒体の例としては図２２および図２３に示すフォーマットを有するものが用いられる。
【０１６７】
多値記録方法の第１３例、第１４例と同様に、まず、光磁気記録媒体を記録再生装置に装着し、光学ヘッドをテスト領域２２注の所望のアドレスに位置付ける。また、磁気ヘッドを当該所望のトラックの近傍に位置付ける。しかる後に、光学ヘッドおよび磁気ヘッドを駆動して、当該テスト領域に、当該光磁気記録媒体に記録しようとする多値記録信号を２種以上の光パルス周期で、レーザ光パワーおよびレーザ光パルス幅の少なくとも一方を変更しつつ記録する。ついで、当該テスト信号を再生して、前記の２種以上の周期の再生信号の各々の信号レベルの平均値の差が一定にすることにより、光磁気記録媒体の記録磁区幅を一定に制御する。
【０１６８】
テスト記録は、図６８あるいは図６９に示すように、多値記録信号の最も振幅の大きな２つのレベル間で２種以上の記録レーザ光パルス周期で行う。上記２つの記録レーザ光パルス周期のうち少なくとも１種の周期は、当該周期の記録磁区が重なり合わない周期に、少なくとも１種の周期は、当該周期の記録磁区が重なり合う周期に設定する。図６８あるいは図６９に示すようなタイミングで極性を切り替えつつ一定強度の記録外部磁界を印加しつつ、記録レーザパワーを段階的に変化させて記録を行う。図７０は図６８の再生信号波形を表している。また、図７１は図６９の再生信号波形を示している。図７０の場合も図７１の場合も、記録レーザパワーを変化させると、記録磁区が重なり合う周期で記録した信号の信号レベルの平均値に対して、記録磁区が重なり合わない周期で記録した信号の信号レベルの平均値が大きく変化する。段階的に変化させたすべての記録条件に対して、２つの周期の平均値の差（Δ1）を検出して、Δ1の値が基準値に最も近い条件を最適記録条件に設定する。このとき、予め設定した基準値が０の場合、光磁気記録媒体ばらつきや回路のＤＣオフセットやドリフトの影響を受けにくいので、基準値が０になるように記録磁区の重ならない周期を、実効的な光スポット径とほぼ等しくすることが望ましい。
【０１６９】
図７２に最適条件検出回路のブロック図の一例を示す。再生されたテスト信号は、上記記録レーザパルス周期より充分低いカットオフ周波数を持ったローパスフィルタを通すことにより、各々の記録レーザパルス周期の再生信号レベルの平均値になる。その上で、信号の最大値と最小値をピークホールドして差を取ることによりΔ1を検出することができる。
【０１７０】
その他については第１３例の記録再生方法と同じであるので、重複を避けるため説明を省略する。
【０１７１】
〈多値記録方法の第１６例〉
本例の多値記録方法は、多値記録用の光磁気記録媒体に、当該光磁気記録媒体が有する安定な記録状態の磁界領域の数よりも多値の記録信号を記録することを特徴とする。光磁気記録媒体としては、前出の第１構成例及び第２構成例に係る光磁気記録媒体を用いることができるが、ここでは４値記録用の光磁気記録媒体（第１構成例に係る光磁気記録媒体。具体的には、図９〜図１３の光磁気記録媒体。）を用いて、１６値の記録を行う場合について説明する。
【０１７２】
まず、光磁気記録媒体をターンテーブル等の媒体駆動部に装着し、透明基板側に光学ヘッドを、保護層側に磁気ヘッドを配置する。媒体駆動部を起動して光磁気記録媒体と光学ヘッド及び磁気ヘッドとを相対的に所定の線速度で駆動し、光学ヘッド及び磁気ヘッドを所定のトラックに位置付ける。しかる後に、光学ヘッドより当該所定の記録トラックに沿って一定強度のレーザビームを照射しつつ、磁気ヘッドより所望の記録信号にてパルス状に信号変調された磁界を印加して信号の記録を行う。
【０１７３】
この場合、図７３に示すように、４値記録信号（００３１２２００１２０３２１３３１１３０２３０１１３２０３２１０）を先頭から２つずつ区切ることによって、（００）（３１）（２２）（００）（１２）（０３）（２１）（３３）（１１）（３０）（２３）（０１）（１３）（２０）（３２）（１０）という信号列に変換し、さらに、各組の第１番目の信号と第２番目の信号とを別個に取りだすことによって、（０３２０１０２３１３２０１２３１）という第１の信号列と、（０１２０２３１３１０３１３０２０）という第２の信号列とに分割する。
【０１７４】
そして、レーザビームが、所望の記録トラックの先頭位置に至ったとき、光学ヘッドより照射されるレーザビームの強度を記録レベルＰ₁ に切り替えると共に、磁気ヘッドより第１の信号列にてパルス状に信号変調された磁界Ｈ₁ を印加する。これによって、図７３（ａ）に示すように、光磁気記録媒体に幅広の第１の書き込み信号列２０１を形成する。
【０１７５】
次いで、レーザビームを、第１の書き込み信号列２０１が形成された記録トラックの先頭位置に再度位置付け、光学ヘッドより照射されるレーザビームの強度を、前記第１の書き込み信号列２０１を書き換え可能なレベルＰ₂ （Ｐ₁＞Ｐ₂）に切り替えると共に、磁気ヘッドより第２の信号列にてパルス状に信号変調された磁界Ｈ₂ を印加する。これによって、図７３（ａ）に示すように、第１の書き込み信号列２０１の中心部に、第１の書き込み信号列２０１の幅よりも狭い第２の書き込み信号列２０２を形成する。なお、第１の書き込み信号列２０１の幅よりも第２の書き込み信号列２０２の幅を小さくし、第１の書き込み信号列２０１の一部を第２の書き込み信号列２０２に書き換えることは、波長が異なる複数個のレーザ光を用いることにより、スポットの大きさを変更することによっても行うことができる。
【０１７６】
記録信号の再生は、第１の書き込み信号列２０１の幅よりもスポット径Ｄが大きな再生用レーザビーム２１０を、記録トラックに沿って照射することにより行える。すなわち、記録トラックに沿って第１の書き込み信号列２０１の幅よりもスポット径Ｄが大きな再生用レーザビーム２１０を照射すると、図７３（ｂ）に示すように、第１及び第２の信号列の信号が共に“３”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“１”の領域と、第１及び第２の信号列の信号が共に“０”の領域とでは、再生用レーザスポット２１０が照射された領域の合計の磁化状態が異なるので、前記各領域における合計の磁化状態に、夫々“０”〜“１５”を割り当てることによって、１６値の記録信号を検出できる。
【０１７７】
かように、本例の記録再生方式によると、４値記録媒体を用いて、信号の１６値記録を実現できるので、安価にして記録情報量が大きい光磁気記録媒体を提供できる。
【０１７８】
なお、磁界変調方式に代えて、光変調方式によっても同様の１６値記録を実行できることは勿論である。
【０１７９】
〈多値記録方法の第１７例〉
本例の多値記録方法は、４値記録用の光磁気記録媒体に、光−磁界変調方式により信号を１６値記録することを特徴とする。
【０１８０】
第１６例の場合と同様に、光磁気記録媒体をターンテーブル等の媒体駆動部に装着し、透明基板側に光学ヘッドを、保護層側に磁気ヘッドを配置する。媒体駆動部を起動して光磁気記録媒体と光学ヘッド及び磁気ヘッドとを相対的に所定の線速度で駆動し、光学ヘッド及び磁気ヘッドを所定のトラックに位置付ける。しかる後に、図７４に示すように、光学ヘッドより当該所定の記録トラックに沿ってパルス状に強度変調されたレーザビームを照射しつつ、磁気ヘッドより所望の記録信号にてパルス状に信号変調された磁界を印加して信号の記録を行う。
【０１８１】
記録信号は、第１６例と同様の方法で、第１の信号列と第２の信号列とに分割する。そして、レーザビームが、所望の記録トラックの先頭位置に至ったとき、光学ヘッドより照射されるレーザビームをパルス状に切り替えると共に、その強度を記録レベルＰ₁ に切り替える。また、磁気ヘッドより第１の信号列にてパルス状に信号変調された磁界Ｈ₁ を印加する。これによって、図７４（ａ）に示すように、光磁気記録媒体に幅広の第１の書き込み信号列２０１を形成する。パルス状の記録用レーザビームは、磁気ヘッドより印加される外部磁界が目標値に到達したタイミングに併せて照射される。
【０１８２】
次いで、レーザビームを、第１の書き込み信号列２０１が形成された記録トラックの先頭位置に再度位置付け、光学ヘッドより照射されるレーザビームをパルス状に切り替えると共に、その強度を、前記第１の書き込み信号列２０１を書き換え可能なレベルＰ₂ （Ｐ₁＞Ｐ₂）に切り替える。また、磁気ヘッドより第２の信号列にてパルス状に信号変調された磁界Ｈ₂ を印加する。これによって、図７４（ａ）に示すように、第１の書き込み信号列２０１の中心部に、第１の書き込み信号列２０１の幅よりも狭い第２の書き込み信号列２０２を形成する。この場合にも、パルス状の記録用レーザビームは、磁気ヘッドより印加される外部磁界が目標値に到達したタイミングに併せて照射される。なお、本例の記録再生方式においては、第１回目の記録時と第２回目の記録時とで記録用レーザビームの発光タイミングを時間ｔだけずらしている。このようにすると、図７５に示すように、第１回目と第２回目の記録用レーザビームの発光タイミングを揃えた場合よりも、各領域より検出される再生信号の波形が、よりシャープになる。時間ｔは、再生信号の波形が、最もシャープになる値に調節される。
【０１８３】
記録信号の再生は、第１６例の場合と同様に、第１の書き込み信号列２０１の幅よりもスポット径Ｄが大きな再生用レーザビーム２１０を、記録トラックに沿って照射することにより行える。すなわち、記録トラックに沿って第１の書き込み信号列２０１の幅よりもスポット径Ｄが大きな再生用レーザビーム２１０を照射すると、図７４（ｂ）に示すように、第１及び第２の信号列の信号が共に“３”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“３”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“２”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“１”の領域と、第１の信号列の信号が“１”で第２の信号列の信号が“０”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“３”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“２”の領域と、第１の信号列の信号が“０”で第２の信号列の信号が“１”の領域と、第１及び第２の信号列の信号が共に“０”の領域とでは、再生用レーザスポット２１０が照射された領域の合計の磁化状態が異なるので、前記各領域における合計の磁化状態に、夫々“０”〜“１５”を割り当てることによって、１６値の記録信号を検出できる。
【０１８４】
本実施例によると、前記第１６例と同様の効果を奏するほか、磁気ヘッドによって印加される外部磁界が目標値に到達したタイミングに併せてパルス状の記録用レーザビームを照射するようにしたので、各磁化ドメインのエッジがシャープになり、ジッタに対するマージンを大きくできる。また、第１回目の記録時と第２回目の記録時とで記録用レーザビームの発光タイミングをずらしたので、第１回目と第２回目の記録用レーザビームの発光タイミングを揃えた場合よりも各領域よりシャープな再生信号を得ることができる。よって、これらの効果より、ピットエッジ記録が可能になる。
【０１８５】
なお、記録信号を３つの信号列に分割し、同一のトラック上にこれら３つの信号列を重ね書きすれば、同様の原理によって、６４値信号記録を行える。
【０１８６】
〈多値記録方法の第１８例〉
本例の多値記録方法は、記録トラックに沿って微小なプリピットが微小な間隔で形成された光磁気記録媒体に対して、信号を記録再生することを特徴とする。この光磁気記録媒体の構成及び用法としては、以下のようなものが考えられる。
【０１８７】
ａ．情報記録領域にデータ単位に分割されたプリピット群を有する基板上に光磁気記録層を形成し、プリピット内又はプリピット間に光磁気信号を記録する。
【０１８８】
ｂ．前記ａ．の媒体の上に、多値記録が可能な記録膜を積層する。
【０１８９】
ｃ．前記ａ．のプリピット群を、トラックごとに規則的に配列する。半径方向に直線上に並べたり、１／２周期ずらしたりする。これにより、クロストークの量子化が可能になる。
【０１９０】
ｄ．前記ａ．の媒体において、プリピットの内と外で、膜の組成や膜厚を変更することもできる。
【０１９１】
ｅ．前記ａ．の媒体のプリピットを再生光スポット径より小さく形成し、その上に磁気超解像が可能な記録膜を積層する。
【０１９２】
ｆ．その他、前記ａ．〜ｅ．の媒体に対して、前記した各種の多値記録方法を適用する。
【０１９３】
光磁気記録媒体においては、記録密度の向上が、最も重大な技術的課題の１つである。記録磁区を微小化し、信号をトラック方向に詰めて記録すれば、記録密度を向上することはできる。しかしながら、記録磁区を微小化すると、隣接した磁区から再生される信号が相互に干渉しやすくなり、分離できなくなる。
【０１９４】
記録トラックに沿って微小なプリピットを微小な間隔で形成すると、記録トラックに沿って再生用レーザビームを照射したとき、光の回折や干渉によってプリピットがある部分からの反射光信号とプリピットがない部分からの反射光信号とが変化するので、その反射光信号（いわゆる和信号）を検出することによって、プリピットの有無を検出できる。一方、磁性膜に記録された光磁気信号（いわゆる差信号）は、プリピットの有無に関係なく、記録磁区の磁化の方向を検出することによって検出できる。したがって、記録磁区をプリピットと位置的に関連付けて形成すれば、記録磁区が微小化しても記録磁区の位置を明確にすることができ、信号の分離が容易になって、記録密度の向上が図れる。
【０１９５】
図７６は、プリピット３０１上に記録磁区３０２を形成した場合を示している。本例の場合には、和信号と差信号が１対１に対応するので、和信号のピークを検出することによって、記録磁区３０２を検出できる。
【０１９６】
図７７（ａ）は、記録磁区３０２の先頭エッジがプリピット３０１に重なるように記録磁区３０２を形成した場合を示し、図７７（ｂ）は、相隣接するプリピット３０１の間に複数（本例では３個）の記録磁区３０２を形成した場合を示す。また、図７７（ｃ）は、プリピット３０１の配列中心と記録磁区３０２の配列中心をずらした場合を示し、図７７（ｄ）は、プリピット３０１の配列中心と記録磁区３０２の配列中心をずらすと共に、相隣接するプリピット３０１の間に複数（本例では３個）の記録磁区３０２を形成した場合を示す。
【０１９７】
図７８（ａ）は、プリピット３０１を凸形に形成した場合を示し、図７８（ｂ）は、プリピット３０１を楕円形に形成した場合を示す。また、図７８ （ｃ）は、２つの凸形のプリピット３０１ａ，３０１ｂ上に１つの記録磁区３０２を形成した場合を示し、図７８（ｄ）は、２つの凹形のプリピット３０１ａ，３０１ｂ上に１つの記録磁区３０２を形成した場合を示す。
【０１９８】
図７９は、プリピット３０１をトラック方向のみならず、トラック間方向にも規則性をもたせて形成した場合を示す。このように、隣接トラック上のプリピット相互の位置関係に規則性をもたせ、これを案内として記録磁区を形成すると、隣接トラックからに記録信号の漏れ込み、いわゆるクロストークのレベルを、記録パターンによって量子化されたレベルにできる。
【０１９９】
図８０は、中央のトラックを再生用レーザスポット２１０の中心が通るように再生用レーザスポット２１０を走査した状態を示す。このようにすると、再生信号レベルは、両側のトラックの記録パターンとの組合せによって、６つのレベルに分離された多値信号として出力される。元の信号は、各トラックの中央を再生用レーザスポット２１０の中心が通るように再生した信号の相互関係により、漏れ込んだ信号をキャンセルして再生する。この場合、１度多値記録として再生され、６段階に分離されているので、クロストークのキャンセルが容易になる。
【０２００】
本例の記録再生方法は、再生光スポット内にレーザの進行方向ないしクロストラック方向に複数の記録ピットが存在し、それらの記録状態の各組合せにより発現する再生信号の各レベルが各々画定された多段階にある記録再生方式であり、多値記録用の光磁気記録媒体のみならず、通常の２値記録用の光磁気記録媒体や磁気超解像形の光磁気記録媒体を用いた信号の記録再生にも応用できる。
【０２０１】
以下に、本発明の他の多値記録方法を列挙する。
【０２０２】
▲１▼透明基板上に積層される各膜の屈折率や膜厚、それに垂直磁化膜のカー回転角などを調整することによって、各記録状態に対応する相対信号出力の間隔を等しくする。例えば３値記録媒体の場合、図８１に示すように、状態“０”、“１”、“２”に対応する記録信号の各レベル間隔を等しくする。このようにすると、記録信号の各レベル間隔の遷移に対する再生信号のＳ／Ｎが均等になり、総合的に信号効率が高められる。本法は、最小記録磁区の大きさが、再生用光のスポット径に対して比較的大きい場合、例えばスポット径の１／２以上である場合に特に有効である。
【０２０３】
▲２▼最小記録磁区の大きさが、再生用光のスポット径よりも小さい場合、特にスポット径の１／２以下の大きさで記録を行う場合、微小磁区の波形間干渉で発生する信号レベルと各記録状態の大きな磁区から発生する信号レベルとが異なるようにする。
【０２０４】
最小記録磁区の大きさが、再生用光のスポット径に対して比較的小さい場合、例えばスポット径の１／２以下である場合には、これが連続すると、再生信号の波形間干渉により信号出力は両状態の中間値をとる。例えば、本発明の多値記録媒体に状態“０”と状態“２”の同じ大きさの微小記録磁区を繰り返し記録した場合、図８２に示すように、状態“１”に対する再生用光のスポット径に対して比較的大きい磁区の再生信号と同じレベルとなり、両者の区別ができなくなる。
【０２０５】
そこで、微小磁区の波形間干渉で発生する信号レベルと各記録状態の大きな磁区から発生する信号レベルとが異なるようにすると、状態“０”、状態“１”、状態“２”、それに状態“０”と状態“１”との間の波形間干渉レベル、状態“０”と状態“２”との間の波形間干渉レベル、状態“１”と状態“２”との間の波形間干渉レベルにそれぞれ信号を割り当てることによって、より高次の多値記録が可能になる。
【０２０６】
各信号レベルは、相互に一致しないようにし、好ましくは等間隔にする。その方法としては、媒体で行う方法と記録方式で行う方法がある。媒体で行う方法としては、図８３に示すように、微小磁区の波形間干渉で発生する信号レベルとは異なる信号レベルに各記録状態の大きな磁区から発生する信号レベルが位置するように、各膜の多重干渉条件を設定する方法がある。また、記録方式で行う方法としては、図８４に示すように、各記録状態の大きな磁区から発生する信号レベルとは異なる位置に、微小磁区の波形間干渉で発生する信号レベルが位置するように、記録磁区の面積比率を制御する方法がある。具体的には、媒体が記録再生装置に挿入された際に、装置が微小記録磁区の面積比率を変化させて記録を試行し、各記録状態の大きな磁区から発生する信号レベルと相互に一致せず、好ましくは等間隔にする面積比を選定するという方法をとることができる。また、これら媒体で行う方法と記録方式で行う方法とを併用することもできる。この併用方式によると、より各信号レベルの調整が容易となり、信号レベル間隔を等間隔にすることができる。また、記録磁区の面積比率を制御することにより、信号レベルを任意の位置に調整することもできる。
【０２０７】
▲３▼多値記録媒体に対するマークエッジ記録方法と、当該方法でマークエッジ記録がされた媒体からの信号再生方法。
図８５に、記録磁区の端部（マークエッジ）に３値の情報を担持させるマークエッジ記録方法、及び当該方法でマークエッジ記録がされた多値記録媒体からの信号再生方法を示す。光磁気記録媒体としては、磁性層に３値の情報を記録可能な光磁気記録媒体が用いられる。
【０２０８】
まず、当該光磁気記録媒体に対するマークエッジ記録方法について説明する。光磁気記録媒体に３値の情報“０”、“１”、“２”を記録するためには、磁性層の磁化状態（磁性層が複数層ある場合には、各磁性層が有する磁化状態の合計の磁化状態）を３段階に切り替える必要がある。それら３段階の磁化状態を夫々Ａ，Ｂ，Ｃ（但し、磁化の大きさは、Ａ＜Ｂ＜Ｃの順に大きくなるとする。）とし、図８５（ｃ）に示すように、▲１▼白地の磁化状態Ａが連続する部分、斜線の磁化状態Ｂから白地の磁化状態Ａに切り替わる部分、格子の磁化状態Ｃから白地の磁化状態Ａに切り替わる部分に“０”の情報を割り当て、▲２▼白地の磁化状態Ａから斜線の磁化状態Ｂに切り替わる部分、斜線の磁化状態Ｂが連続する部分、格子の磁化状態Ｃから斜線の磁化状態Ｂに切り替わる部分に“１”の情報を割り当て、▲３▼白地の磁化状態Ａから格子の磁化状態Ｃに切り替わる部分、斜線の磁化状態Ｂから格子の磁化状態Ｃに切り替わる部分、格子の磁化状態Ｃが連続する部分に“２”の情報を割り当てて情報の記録を行うと、例えば３値情報（１０２０２２０１２１０）は、図８５（ａ）に示すマーク列で記録できる。
【０２０９】
次に、前記の方法で３値の情報がマークエッジ記録された媒体からの信号再生方法について説明する。図８５（ａ）のマーク列に沿って再生用光を照射すると、各記録磁区の磁化の大きさに対応して、図８５（ｂ）の再生信号波形が得られる。Ａの記録磁区から検出される再生信号出力をα、Ｂの記録磁区から検出される再生信号出力をβ、Ｃの記録磁区から検出される再生信号出力をγとしたとき、α＜ｓ₂ ＜β＜ｓ₁ ＜γという条件を満たす２つの異なるスライスレベルｓ₁ ，ｓ₂ にて、図８５（ｂ）の再生信号波形をスライスし、各スライスレベルｓ₁ ，ｓ₂ と再生信号出力とのクロス点を検出する。図８５（ｂ）の中欄に、各スライスレベルｓ₁ ，ｓ₂ で検出される信号の有無を、記号「○」又「−」で示す。当欄の上の列はスライスレベルｓ₁ で検出される信号の検出パターンを示し、下の行はスライスレベルｓ₂ で検出される信号の検出パターンを示している。これらの記載において、記号「○」はクロス点が検出された場合を表わし、記号「−」はクロス点が検出されない場合を表わす。
【０２１０】
この図から明らかなように、本例の場合には、スライスレベルｓ₁ の検出信号とスライスレベルｓ₂ の検出信号との組合せが、スライスレベルｓ₁ の検出信号が「−」でスライスレベルｓ₂ の検出信号が「○」の場合（以下、この組合せを「−，○」と表記する。以下同様に、スライスレベルｓ₁ の検出信号を「」内の先に、スライスレベルｓ₂ のクロス点を後に記載する。）と、「○，−」の場合と、「○，○」の場合と、「−，−」の場合の４種類になる。
【０２１１】
そこで、図８５（ｄ）に示すように、各信号検出部の１つ前のデータを記憶しておき、▲１▼当該１つ前のデータが「○，○」で検出信号が「−，−」の場合、１つ前のデータが「−，○」で検出信号が「○，−」の場合、それに１つ前のデータが「−，−」で検出信号が「○，○」の場合に、再生データの“２”を割り当て、▲２▼１つ前のデータが「○，○」で検出信号が「○，−」の場合、１つ前のデータが「−，○」で検出信号が「−，−」の場合、それに１つ前のデータが 「−，−」で検出信号が「−，○」の場合に、再生データの“１”を割り当て、さらには、▲３▼１つ前のデータが「○，○」で検出信号が「○，○」の場合、１つ前のデータが「−，○」で検出信号が「−，○」の場合、それに１つ前のデータが「−，−」で検出信号が「−，−」の場合に、再生データの“０”を割り当てることによって、図１０３（ｂ）の最下欄に示すように、元の３値情報（１０２０２２０１２１０）を再生することができる。
【０２１２】
なお、図８５においては、３値記録用の光磁気記録媒体を用いた場合のマークエッジ記録再生方法を例にとって説明したが、２値記録用の光磁気記録媒体又は４値記録以上の多値記録用光磁気記録媒体を用いた場合にも、前記と同様にして、情報のマークエッジ記録再生を実行することができる。
【０２１３】
また、図８５の例においては、白地の磁化状態Ａが連続する部分、斜線の磁化状態Ｂから白地の磁化状態Ａに切り替わる部分、格子の磁化状態Ｃから白地の磁化状態Ａに切り替わる部分に“０”の情報を割り当て、白地の磁化状態Ａから斜線の磁化状態Ｂに切り替わる部分、斜線の磁化状態Ｂが連続する部分、格子の磁化状態Ｃから斜線の磁化状態Ｂに切り替わる部分に“１”の情報を割り当て、白地の磁化状態Ａから格子の磁化状態Ｃに切り替わる部分、斜線の磁化状態Ｂから格子の磁化状態Ｃに切り替わる部分、格子の磁化状態Ｃが連続する部分に“２”の情報を割り当てて情報の記録を行ったが、いかなる磁化状態の変化にいかなる情報を割り当てるかは、本実施例に拘らず、必要に応じて適宜変更することができる。
【０２１４】
以下に、光磁気記録媒体の多値記録に適用可能な磁気ヘッド装置の構成例を示す。
【０２１５】
〈磁気ヘッド装置の第１構成例〉
本例の磁気ヘッド装置は、図８６に示すように、１つの磁気回路に２つの巻線を巻回してなり、それらの巻線を夫々独立に駆動できるようにしたことを特徴とする。この磁気ヘッド装置は、光磁気記録媒体の保護膜側に配置される。
【０２１６】
本例の磁気ヘッド装置は、多値記録方法の第１例、第４例、第５例に適用できる。すなわち、これらの多値記録方法を実行する際、２つの巻線に電流を印加する磁気ヘッド駆動回路１と磁気ヘッド駆動回路２を記録クロックに同期して独立に駆動することにより、光磁気記録媒体に多値の外部磁界を印加することができるので、これと同時に、記録クロックに同期した光パルスを照射することによって、当該光パルスの照射部に信号を多値記録できる。
【０２１７】
また、本例の磁気ヘッド装置は、多値記録方法の第２例、第３例に適用できる。すなわち、一方の巻線と磁気ヘッド駆動回路とで共振回路を構成し、記録クロックと同期した一定周波数の磁界を発生させると共に、他方の巻線に一定の電流を印加して一定のバイアス磁界を発生させることにより、磁界ゼロからオフセットした一定周期の磁界を光磁気記録媒体に印加することができる。
【０２１８】
なお、前記構成例においては、巻線数が２の場合を例にとって説明したが、巻線数が３以上の場合にも同様に構成できる。
【０２１９】
〈磁気ヘッド装置の第２構成例〉
本例の磁気ヘッド装置は、図８７に示すように、互いに独立して駆動可能な２つの磁気ヘッドを、互いに近接して配置したことを特徴とする。この磁気ヘッド装置も、光磁気記録媒体の保護膜側に配置される。
【０２２０】
本例の磁気ヘッド装置は、多値記録方法の第４例、第５例に適用できる。すなわち、これらの多値記録方法を実行する際、磁気ヘッド１と磁気ヘッド２とを記録クロックに同期して独立に駆動することにより、光磁気記録媒体に多値の外部磁界を印加することができるので、これと同時に、記録クロックに同期した光パルスを照射することによって、当該光パルスの照射部に信号を多値記録できる。
【０２２１】
また、本例の磁気ヘッド装置は、多値記録方法の第２例、第３例に適用できる。すなわち、一方の磁気ヘッドと磁気ヘッド駆動回路とで共振回路を構成し、記録クロックと同期した一定周波数の磁界を発生させると共に、他方の磁気ヘッドに一定の電流を印加して一定のバイアス磁界を発生させることにより、磁界ゼロからオフセットした一定周期の磁界を光磁気記録媒体に印加することができる。
【０２２２】
〈磁気ヘッド装置の第３構成例〉
本例の磁気ヘッド装置は、図８８に示すように、２つの磁気ヘッドを互いに近接して配置すると共に、これら２つの磁気ヘッドに近接してバイアス磁界印加用の永久磁石を配置したことを特徴とする。２つの磁気ヘッドは、互いに独立して駆動できるように構成される。本例の磁気ヘッド装置も、光磁気記録媒体の保護膜側に配置される。
【０２２３】
本例の磁気ヘッド装置は、多値記録方法の第４例、第５例に適用できる。すなわち、これらの多値記録方法を実行する際、磁気ヘッド１と磁気ヘッド２とを記録クロックに同期して独立に駆動することにより、光磁気記録媒体に多値の外部磁界を印加することができる。また、永久磁石によって、一定のバイアス磁界を光磁気記録媒体に印加することができる。したがって、磁界の印加と同時に、記録クロックに同期した光パルスを照射することによって、当該光パルスの照射部に信号を多値記録できる。
【０２２４】
また、本例の磁気ヘッド装置は、多値記録方法の第２例、第３例に適用できる。すなわち、磁気ヘッドと磁気ヘッド駆動回路とで共振回路を構成し、記録クロックと同期した一定周波数の磁界を発生させると共に、永久磁石により一定のバイアス磁界を印加することにより、磁界ゼロからオフセットした一定周期の磁界を光磁気記録媒体に印加することができる。
【０２２５】
本例の磁気ヘッド装置は、バイアス磁界の印加用に永久磁石を備えたので、磁気ヘッドに直流分の電流を加える必要がない。よって、消費電力の低減と信号伝送レートの高速化を図ることができる。
【０２２６】
〈磁気ヘッド装置の第４構成例〉
本例の磁気ヘッド装置は、図８９に示すように、２つの磁気ヘッドを互いに近接して光磁気記録媒体の保護膜側に配置すると共に、バイアス磁界として、絞り込みレンズアクチュエータからの漏洩磁界を利用したことを特徴とする。その他については、第３構成例に係る磁気ヘッド装置と同じであるので、説明を省略する。
【０２２７】
〈磁気ヘッド装置の第５構成例〉
本例の磁気ヘッド装置は、図９０に示すように、１つの磁気ヘッドとバイアス磁界印加用の永久磁石とを互いに近接して光磁気記録媒体の保護膜側に配置したことを特徴とする。
【０２２８】
〈磁気ヘッド装置の第６構成例〉
本例の磁気ヘッド装置は、図９１に示すように、１つの磁気ヘッドを光磁気記録媒体の保護膜側に配置すると共に、バイアス磁界として、絞り込みレンズアクチュエータからの漏洩磁界を利用したことを特徴とする。
【０２２９】
〈磁気ヘッド装置の第７構成例〉
本例の磁気ヘッド装置は、図９２に示すように、２つの磁気ヘッドを互いに近接して配置すると共に、これら２つの磁気ヘッドに近接してバイアス磁界印加用の電磁コイルを配置したことを特徴とする。本例の磁気ヘッド装置も、光磁気記録媒体の保護膜側に配置される。
【０２３０】
〈磁気ヘッド装置の第８構成例〉
本例の磁気ヘッド装置は、図９３に示すように、２つの磁気ヘッドを互いに近接して光磁気記録媒体の保護膜側に配置すると共に、バイアス磁界印加用の電磁コイルを絞り込みレンズアクチュエータの周囲に配置したことを特徴とする。本例の磁気ヘッド装置も、光磁気記録媒体の保護膜側に配置される。
【０２３１】
なお、前記実施例に掲げたのは本発明の実施の一例に過ぎず、その他にも、本発明に係る任意の媒体と任意の記録再生方式と記録再生装置とを組み合わせることによって、各種の信号記録を行うことができる。特に、磁気ヘッド装置については、前記構成例の記載に限定されるものではなく、磁気ヘッドの巻線数、磁気ヘッドの数量及び配置、それにバイアス磁界の印加手段である永久磁石や電磁コイルの数量や配置等を適宜変更して用いることができる。
【０２３２】
なお、前記実施例においては、説明を容易にするために、光磁気記録媒体の膜構造と、そのフォーマットと、多値記録再生方法と、磁気ヘッド装置とに分けて説明し、それらの組合せについては代表的なものだけを選択的に記載した。したがって、本発明の要旨は、前記実施例に掲げた組合せに限定されるものではなく、前記実施例に記載された任意の光磁気記録媒体と多値記録再生方法と磁気ヘッド装置の組合せをもって、情報の多値記録を実行することができる。
【０２３３】
その他、本発明の特徴を逸脱しない範囲で、前記実施例で説明した光磁気記録媒体、記録再生方式、それに磁気ヘッド装置を変更することは、必要に応じて適宜行うことができる。例えば、複数の記録再生用レーザ光の照射部を有する光磁気ヘッドを備えた記録再生装置を用いて情報の記録再生を行う等の記録再生方法をとることも可能である。
【０２３４】
【発明の効果】
以上説明したように、本発明によると、より簡単な膜の積層構造で、より高密度な信号記録を実現できる。また、本発明の光磁気記録媒体は、各記録状態が外部磁界の変動に対してきわめて安定であり、各記録層の磁気特性や記録再生時のレーザビーム強度それに外部磁界強度を微妙にマッチングさせる必要がないので、安定性、量産性、実用性に優れた光磁気記録再生システムを構築できる。
【図面の簡単な説明】
【図１】本発明に係る光磁気記録媒体の特性を例示するグラフ図である。
【図２】本発明に係る多値記録方法の原理を示す説明図である。
【図３】本発明に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図４】本発明に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図５】 参考例に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図６】本発明に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図７】本発明に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図８】本発明に係る光磁気記録媒体の膜構成と磁化特性との関係を例示する説明図である。
【図９】第１構成例に係る光磁気記録媒体の説明図である。
【図１０】第１実施例に係る光磁気記録媒体を模式的に示す要部断面図である。
【図１１】第２実施例に係る光磁気記録媒体を模式的に示す要部断面図である。
【図１２】第３実施例に係る光磁気記録媒体を模式的に示す要部断面図である。
【図１３】第４実施例に係る光磁気記録媒体を模式的に示す要部断面図である。
【図１４】第２構成例に係る光磁気記録媒体を模式的に示す要部断面図である。
【図１５】第２構成例に係る光磁気記録媒体を用いた磁気超解像再生方式の第１例を示す説明図である。
【図１６】第２構成例に係る光磁気記録媒体を用いた磁気超解像再生方式の第２例を示す説明図である。
【図１７】第２構成例に係る光磁気記録媒体を用いた磁気超解像再生方式の第３例を示す説明図である。
【図１８】第２構成例に係る光磁気記録媒体を用いた磁気超解像再生方式の第４例を示す説明図である。
【図１９】第２構成例に含まれる各光磁気記録媒体の膜構造を示す表図である。
【図２０】サンプルサーボ方式の光磁気記録媒体に形成されるプリフォーマットパターンの説明図である。
【図２１】図２０中のサーボ領域の説明図である。
【図２２】ＣＡＶ方式の光ディスクに設けられるテスト領域の実施例図である。
【図２３】ＺＣＡＶ方式の光ディスクに設けられるテスト領域の実施例図である。
【図２４】第１例に係る多値記録方式の実行に使用される畳み込み符号器の構成図である。
【図２５】図２４の畳み込み符号器の出力の状態遷移を示す説明図である。
【図２６】第１例に係る多値記録再生方式を実行する多値記録再生装置の構成図である。
【図２７】本発明に係る多値記録再生方式の第２例を示す説明図である。
【図２８】多値記録再生方式の第２例に係る外部磁界強度の信号変調方式を示す説明図である。
【図２９】多値記録再生方式の第２例に係る外部磁界強度変調回路の第１例を示す構成図である。
【図３０】多値記録再生方式の第２例に係る外部磁界強度変調回路の第２例を示す構成図である。
【図３１】第２例の多値記録再生方式によって記録された磁化ドメインの記録状態を示す説明図である。
【図３２】外部磁界印加回路の一例を示す回路図である。
【図３３】図３１の光磁気記録媒体から信号を読みだす信号再生回路の構成図である。
【図３４】第２例に係る多値記録再生方式の効果を示す説明図である。
【図３５】第３例に係る多値記録再生方式に適用されるレーザ照射タイミング変調回路の構成図である。
【図３６】図３５の回路の動作を示すタイミングチャートである。
【図３７】第３例に係る多値記録再生方式に適用される信号再生回路の構成図である。
【図３８】図３７の回路の動作説明図である。
【図３９】第４例に係る多値記録再生方式に適用されるレーザ強度変調回路の構成図である。
【図４０】図３９の回路の動作を示すタイミングチャートである。
【図４１】第４例に係る多値記録再生方式に適用される信号再生回路の構成図である。
【図４２】図４１の回路の動作説明図である。
【図４３】多値記録再生方式の第５例に適用される印加磁界と照射レーザ強度の組合せの第１例を示す説明図である。
【図４４】多値記録再生方式の第５例に適用される印加磁界と照射レーザ強度の組合せの第２例を示す説明図である。
【図４５】多値記録再生方式の第５例に適用される印加磁界と照射レーザ強度の組合せの第３例を示す説明図である。
【図４６】多値記録再生方式の第６例に適用される光磁気記録媒体の再生信号出力特性を示すグラフ図である。
【図４７】第６例に属する多値記録再生方式の説明図である。
【図４８】第６例に属する他の多値記録再生方式の説明図である。
【図４９】多値記録再生方式の第７例に係るテスト信号の説明図である。
【図５０】多値記録再生方式の第７例に係るテスト信号再生回路の構成図である。
【図５１】多値記録再生方式の第８例に係るテスト信号の説明図である。
【図５２】多値記録再生方式の第９例に係るテスト信号再生回路の構成図である。
【図５３】多値記録再生方式の第１０例を示す説明図である。
【図５４】多値記録再生方式の第１０例に属するマークエッジ記録方法の第１例を示す説明図である。
【図５５】多値記録再生方式の第１０例に属するマークエッジ記録方法の第２例を示す説明図である。
【図５６】多値記録再生方式の第１０例に属するマークエッジ記録方法の第３例を示す説明図である。
【図５７】多値記録再生方式の第１０例に属するマークエッジ記録方法の第４例を示す説明図である。
【図５８】多値記録再生方式の第１０例に属するマークエッジ記録方法の第５例を示す説明図である。
【図５９】多値記録再生方式の第１０例に属するマークエッジ記録方法の第６例を示す説明図である。
【図６０】多値記録再生方式の第１１例を示す説明図である。
【図６１】多値記録再生方式の第１２例を示す説明図である。
【図６２】サンプルサーボ方式の光磁気記録媒体に好適な記録再生装置の構成図である。
【図６３】図６２の記録再生装置に適用されるＤＣレベル補正回路の回路図である。
【図６４】多値記録再生方式の第１３例を示す説明図である。
【図６５】第１３例に係る多値記録再生方式に適用される最適条件検出回路の一例を示す構成図である。
【図６６】多値記録再生方式の第１４例を示す説明図である。
【図６７】第１４例に係る多値記録再生方式に適用される最適条件検出回路の一例を示す構成図である。
【図６８】多値記録再生方式の第１５例に属するテスト信号記録方法の第１例を示す説明図である。
【図６９】多値記録再生方式の第１５例に属するテスト信号記録方法の第２例を示す説明図である。
【図７０】図６８の方法で記録されたテスト信号の再生信号波形を示す波形図である。
【図７１】図６９の方法で記録されたテスト信号の再生信号波形を示す波形図である。
【図７２】第１５例に係る多値記録再生方式に適用される最適条件検出回路を示す構成図である。
【図７３】多値記録再生方式の第１６例を示す説明図である。
【図７４】多値記録再生方式の第１７例を示す説明図である。
【図７５】第１７例に係る多値記録再生方式の効果を示す説明図である。
【図７６】多値記録再生方式の第１８例に属するピット上記録方法の第１例を示す説明図である。
【図７７】多値記録再生方式の第１８例に属するピット上記録方法の第２例を示す説明図である。
【図７８】多値記録再生方式の第１８例に属するピット上記録方法の第３例を示す説明図である。
【図７９】多値記録再生方式の第１８例に属するピット上記録方法の第４例を示す説明図である。
【図８０】多値記録再生方式の第１８例に属するピット上記録方法の第５例を示す説明図である。
【図８１】本発明に係る多値記録再生方式の他の例を示す説明図である。
【図８２】本発明に係る多値記録再生方式の他の例を示す説明図である。
【図８３】本発明に係る多値記録再生方式の他の例を示す説明図である。
【図８４】本発明に係る多値記録再生方式の他の例を示す説明図である。
【図８５】本発明に係る多値記録再生方式の他の例を示す説明図である。
【図８６】磁気ヘッド装置の第１例を示す構成図である。
【図８７】磁気ヘッド装置の第２例を示す構成図である。
【図８８】磁気ヘッド装置の第３例を示す構成図である。
【図８９】磁気ヘッド装置の第４例を示す構成図である。
【図９０】磁気ヘッド装置の第５例を示す構成図である。
【図９１】磁気ヘッド装置の第６例を示す構成図である。
【図９２】磁気ヘッド装置の第７例を示す構成図である。
【図９３】磁気ヘッド装置の第８例を示す構成図である。
【図９４】従来技術の説明図である。
【図９５】従来技術の説明図である。
【図９６】外部磁界に対して２つの記録状態が存在する記録層の外部磁界特性を例示するグラフ図である。
【図９７】外部磁界に対して１つの記録状態が存在する記録層の外部磁界特性を例示するグラフ図である。
【図９８】本発明に係る光磁気記録媒体の多値記録原理の第１例を示す説明図である。
【図９９】本発明に係る光磁気記録媒体の多値記録原理の第２例を示す説明図である。
【図１００】本発明に係る光磁気記録媒体の多値記録原理の第３例を示す説明図である。
【符号の説明】
１ 透明基板
２ プリフォーマットパターン
３ 第１誘電体層
４ 第１磁性層
４ａ 非晶質垂直磁化膜
４ｂ 補助磁性膜
５ 第２誘電体層
６ 第２磁性層
７ 第３誘電体層
８ 反射膜
９ 保護膜
１１ 記録トラック
１２ データ記録単位
１３ ＩＤ領域
１４ サーボ領域
１５ データ領域
１６ トラッキングピット
１７ テスト領域
１８ クロックピット
２１ ユーザ領域
２２ テスト領域
２０１ 第１の書き込み信号列
２０２ 第２の書き込み信号列
２１０ 再生用レーザビーム
３０１ プリピット
３０２ 記録磁区[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magneto-optical recording medium, and more particularly to a laminated structure of magnetic layers in a magneto-optical recording medium capable of multi-value recording.
[0002]
[Prior art]
In the field of magneto-optical recording media, increasing the recording density has become one of the most important technical issues. Conventionally, as a means for increasing the density of a magneto-optical recording medium, for example, page 63 of the 13th Annual Meeting of the Japan Society of Applied Magnetics (published in 1989), Japanese Journal of Applied Physics, Vol. 28 (1989) As described in Supplement 28-3 pp.343-347, a method for multi-level recording of signals has been proposed. The known multilevel recording method is a method of selectively reversing the magnetization of a specific magnetic layer by stacking multiple magnetic layers with different coercive forces and modulating the magnetic field strength applied to the magnetic layer in multiple steps. It is to let you. According to these systems, it is said that four-value recording of signals becomes possible by providing three magnetic layers having different coercive forces.
[0003]
[Problems to be solved by the invention]
However, according to the multilevel recording method according to the known example, when the magneto-optical recording medium is irradiated with a laser beam during signal recording to raise the temperature of each magnetic layer to near the Curie temperature, the coercive force of each magnetic layer is reduced. Since the difference is almost eliminated, it is practically difficult to selectively reverse the magnetization of each magnetic layer. If the magnetic properties of each magnetic layer are strictly adjusted, and the laser intensity and external magnetic field intensity during recording are strictly controlled, it is possible to selectively reverse the magnetization of each magnetic layer at the laboratory level. Even if it becomes, it is impossible to mass-produce such a magneto-optical recording medium and a recording / reproducing apparatus from the viewpoint of cost. Also, since the margin for fluctuations in the laser intensity and external magnetic field intensity during recording is extremely small, it is impossible to maintain a stable recording / reproducing state for a long period of time, which is not practical. In addition, if the recording of signals is performed in a state where the difference in coercive force of each magnetic layer is sufficiently large without raising the temperature of each magnetic layer to the vicinity of the Curie temperature, such inconvenience does not occur. Since a large magnetic field is required for recording and erasing signals, the magnetic field generator such as the magnetic head is enlarged, resulting in another serious inconvenience such as an increase in the size of the recording / reproducing device and an increase in power consumption. Is virtually impossible.
[0004]
Hereinafter, inconveniences of the prior art will be described in more detail with reference to FIG. Here, for ease of explanation, light in which two layers of magnetic films (magnetic layers) having coercive force temperature characteristics indicated by symbols A and B in FIG. 94B are stacked on a substrate are used. A magnetic recording medium will be described as an example.
[0005]
(1) The recording laser beam irradiated portion is heated to a temperature equal to or higher than the Curie temperature of each magnetic layer, so that the coercive force of each magnetic layer differs greatly at room temperature as shown in FIG. However, the difference is remarkably reduced in the temperature rising portion. Therefore, it is practically difficult to selectively reverse the magnetization of each magnetic layer.
[0006]
{Circle around (2)} As shown in FIG. 94A, the recording laser beam irradiating portion has a steep temperature distribution reaching from the room temperature to the Curie temperature or higher in its minute region. Therefore, the coercive force distribution in each magnetic layer in the corresponding region also becomes abrupt as shown in FIG. 94C, and the size of the recording domain becomes slightly no matter what size the applied magnetic field is set. It only changes, and the two magnetic layers cannot be recorded separately by the magnitude of the applied magnetic field.
[0007]
(3) The carrier-to-noise ratio of the signal read from each of the magnetic layers A and B is as shown in FIG. 94 (d) with respect to the external magnetic field intensity at the time of recording. That is, the carrier-to-noise ratio of the signal read from the magnetic layer A and the carrier-to-noise ratio of the signal read from the magnetic layer B are the transition between the unrecorded area and the recorded area with respect to the external magnetic field strength during recording. The area is almost overlapped, and is slightly shifted due to the difference in the leakage magnetic field to the recording part due to the difference in magnetization. Therefore, in the magneto-optical recording medium in which these magnetic layers A and B are laminated, the carrier-to-noise ratio of the read signal has only one stable recording state as shown in FIG. It is impossible to multi-value the recording signal by switching the magnetic field.
[0008]
{Circle over (4)} Further, the conventional technique has a disadvantage that direct signal overwriting cannot be performed.
That is, for example, the magnetic layer (A layer) having A coercive force-temperature characteristics and the magnetic layer (B layer) having B coercive force-temperature characteristics shown in FIG. In the magneto-optical recording medium, the H shown in FIG.₁ When an external magnetic field having a magnitude of is applied, only the B layer is reversed in magnetization as shown in FIG. 95 (b), and H shown in FIG. 94 (b).₂ When an external magnetic field of a magnitude of is applied, both the A layer and the B layer are reversed in magnetization as shown in FIG. Therefore, when the state shown in FIG. 95B is to be recorded on the state shown in FIG.₂ After applying the magnetic field to return to the initial state {Fig. 95 (a)}, H₁ Unless the magnetic field is applied in the recording direction and recording is performed again, the state shown in FIG. 95B cannot be achieved, and direct overwriting of the signal is impossible.
[0009]
(5) Further, when a signal is recorded on this magneto-optical recording medium by, for example, a magnetic field modulation method, when a signal is recorded on a magnetic film having a larger coercive force by applying a larger external magnetic field, the external magnetic field is set to a predetermined value. In the transition process until reaching the value, the coercive force always passes the value of the recording magnetic field with respect to the magnetic film with a smaller value, so that a recording part with a small external magnetic field is always formed around the recording part with a larger external magnetic field. For this reason, not only a high S / N reproduction signal cannot be obtained, but if the signal is recorded at a high density, is it a recorded part by a larger external magnetic field or a recorded part by an original smaller external magnetic field? However, it is difficult to discriminate the recording density and the recording density cannot be increased. Such inconvenience also occurs when signals are recorded by the light modulation method.
[0010]
The present invention has been made to solve such deficiencies of the prior art, and the object thereof is to allow a recording state corresponding to each value in multi-value recording to exist stably against an external magnetic field, and to achieve multi-value recording. Provides a magneto-optical recording medium capable of recording and erasing signals with a small external magnetic field and a small output laser and realizing signal recording with high S / N and high recording density. There is to do.
[0011]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention has a plurality of magnetic layers laminated directly or via a nonmagnetic layer in a magneto-optical recording medium, and at least one of the plurality of magnetic layers includes at least one magnetic layer. , Mainly composed of rare earth and transition metalAn amorphous alloy consisting of a ferrimagnetic material in which the sublattice magnetic moment of rare earth atoms is dominant from room temperature to Curie temperature than the sublattice magnetic moment of transition metal atomsPerpendicular magnetization film and this perpendicular magnetization filmAnd an auxiliary magnetic film made of a PtCo alloy magnetically coupled by exchange coupling, and when an external magnetic field is applied,In two different field strength rangesIt has a peak of change of the carrier wave of the optical modulation recording signal,The other magnetic layer does not have an auxiliary magnetic film,When it is composed of a perpendicular magnetic film and an external magnetic field is applied,Different from the magnetic layer of 1OneIn the range of magnetic field strengthBy applying an external magnetic field having a peak of change in the carrier wave of the optical modulation recording signal and having different four-step magnetic field strengths, a four-value signal can be directly overwritten as a whole.It was configured as follows.
[0012]
Specifically, first of all, a first magnetic layer having an auxiliary magnetic film and having a stable magnetization state in two different magnetic field strength ranges with respect to an applied external magnetic field, and the auxiliary magnetic film And a second magnetic layer having one stable magnetization state in a range of magnetic field strength different from that of the first magnetic layer, and switching the magnitude of the external magnetic field in four steps The configuration is such that four-value recording of signals is possible.
[0013]
Second, the first magnetic layer has an auxiliary magnetic film and has a stable magnetization state in two different magnetic field strength ranges with respect to the applied external magnetic field, and the auxiliary magnetic film. It has a second magnetic layer with two stable magnetization states in a different magnetic field strength range from the one magnetic layer, and can record signals in four values by switching the magnitude of the external magnetic field in four stages. It was configured to be.
[0014]
Third, among the magnetic layers constituting the magneto-optical recording medium, when the reproducing laser beam is irradiated on the reproducing laser beam incident side of at least one of the magnetic layers, the reproducing laser is applied to the magnetic layer. An opening portion forming layer for thermo-magnetically forming an opening portion smaller than the light spot diameter is provided.
[0015]
Fourth, among the magnetic layers constituting the magneto-optical recording medium, when the reproducing laser beam is irradiated on at least one of the magnetic layers, the reproducing laser beam is applied to the magnetic layer. An opening forming layer and a cutting layer were provided for thermo-magnetically forming an opening smaller than the light spot diameter.
[0016]
Of the magnetic layers in the first to fourth magneto-optical recording media, at least one of the magnetic layers is composed of a perpendicular magnetization film and an auxiliary magnetic film magnetically coupled to the perpendicular magnetization film. be able to. As the perpendicular magnetization film, any known perpendicular magnetization film can be used, but an amorphous alloy of a rare earth and a transition metal is particularly preferable because of its large magneto-optical effect. As the auxiliary magnetic film, a film made of a magnetic material that becomes an in-plane magnetization film at least at room temperature can be used. In this case, the magnetic layer composed of the auxiliary magnetic film and the perpendicular magnetization film can have a stable magnetization state in two different magnetic field strength ranges with respect to the applied external magnetic field. The auxiliary magnetic film is preferably a magnetic thin film having a thickness of about 1 to 30 mm.
[0017]
With respect to the preformatting of the magneto-optical recording medium, the data recording area is divided into a plurality of data recording units, and each signal included in the multilevel recording signal recorded in the data recording unit is formed at the head of each data recording unit. A test area for setting a slice level and / or a test area for generating a timing signal serving as a reference for detecting an edge of a multilevel recording signal recorded in the data recording unit is provided. In addition, a tracking pit for performing tracking control of a recording or reproducing laser beam is provided at the beginning of the data recording unit together with the test area or separately from the test area, and is used for recording / reproducing of a multilevel recording signal. An embedded pit for drawing a clock signal to be drawn is provided. Further, a test area for detecting optimum recording conditions is provided in an area other than the user area where a user accesses to record, reproduce, and erase signals.
[0018]
A first magnetic layer having a stable magnetization state in two different magnetic field strength ranges with respect to an applied external magnetic field, and one stable magnetization state in a different magnetic field strength range from the first magnetic layer When a magneto-optical recording medium laminated with a second magnetic layer having a magnetic field is used, four different levels of external magnetic fields corresponding to the respective magnetization states of each magnetic layer can be applied to enable quaternary recording of signals. Become. In addition, the first magnetic layer having a stable magnetization state in two different magnetic field strength ranges with respect to the applied external magnetic field, and two stable magnetic field strength ranges from the first magnetic layer Even in the case of using a magneto-optical recording medium in which a second magnetic layer having a magnetization state is laminated, by applying four different external magnetic fields corresponding to each magnetization state of each magnetic layer, the signal 4 Value recording is possible.
[0019]
  That is, the first magnetic layer formed by laminating a perpendicular magnetization film and a predetermined auxiliary magnetic film is disclosed in Japanese Patent Application No. 3-210430 and Japanese Patent Application No. 4-153882 by the inventors of the present application. 96), the sublattice magnetic moment of the transition metal in the perpendicular magnetized film is easily reversed in the direction of the exchange coupling magnetic field by the action of the auxiliary magnetic film. For example, as shown in FIG. The carrier-to-noise ratio of the optical modulation recording signal with respect to the external magnetic field has two peaks (recording state). On the other hand, since the second magnetic layer having no auxiliary magnetic film is not affected by the auxiliary magnetic film, for example, as shown in FIG. 97, the carrier-to-noise ratio of the optical modulation recording signal with respect to the external magnetic field has one peak. It has. In addition, the first magnetic layer formed by stacking the perpendicular magnetization film and the predetermined auxiliary magnetic film can easily cause the sublattice magnetic moment of the transition metal in the perpendicular magnetization film in the direction of the exchange coupling magnetic field by the action of the auxiliary magnetic layer. Since reversal occurs, the magnetization direction of the entire magnetic layer can be directed to the external magnetic field direction or the opposite direction. On the other hand, the second magnetic layer that does not have an auxiliary magnetic layer and has one stable magnetization state in a range of magnetic field strength different from that of the first magnetic layer is easily oriented in the direction of the external magnetic field in the elevated temperature state. In addition, the magnetization direction of the entire magnetic layer is reversed. The predetermined auxiliary magnetic film anddo itIsAs described above, a magnetic material that becomes an in-plane magnetization film at least at room temperature can be used.Magnetic material whose Curie temperature is the same as the Curie temperature of the perpendicular magnetization film or Magnetic material whose Curie temperature is lower than the Curie temperature of the perpendicular magnetization filmIs preferably used.
[0020]
Therefore, for example, as shown in FIG. 98 (a), the first magnetic layer A made of a ferrimagnetic material in which the sublattice magnetic moment of the rare earth atom is more dominant than the sublattice magnetic moment of the transition metal atom from room temperature to the Curie temperature; A second magnetic layer B made of a ferrimagnetic material in which the sublattice magnetic moment of the transition metal atom is more dominant than the sublattice magnetic moment of the rare earth atom from room temperature to the Curie temperature is laminated, and the downward external magnetic field is applied to the external magnetic field in the recording direction. When recording the signal with the upward external magnetic field as the external magnetic field in the erasing direction,
(i) An external magnetic field H having such a magnitude that the direction of the entire magnetization of the first magnetic layer A can be oriented in the erasing direction.₀ (External magnetic field in region (1) shown in FIG. 96) is applied in the erasing direction, so that the sublattice magnetic moment of the transition metal atoms in the first magnetic layer A is set in the recording direction and the transition metal atoms in the second magnetic layer B The sublattice magnetic moment can be directed in the erasing direction.
(ii) An external magnetic field H having a magnitude capable of directing the entire magnetization direction of the first magnetic layer A in the recording direction.₁ By applying (external magnetic field in region (2) shown in FIG. 96) in the erasing direction, both the sublattice magnetic moments of the transition metal atoms of the first magnetic layer A and the second magnetic layer B can be directed in the erasing direction. it can.
(iii) The external magnetic field H having such a magnitude that the direction of the entire magnetization of the first magnetic layer A can be oriented in the erasing direction.₂ By applying (external magnetic field in region (3) shown in FIG. 96) in the recording direction, the sublattice magnetic moments of the transition metal atoms of the first magnetic layer A and the second magnetic layer B can be directed together in the recording direction. it can.
(iv) An external magnetic field H having such a magnitude that the direction of the entire magnetization of the first magnetic layer A can be oriented in the recording direction._Three (External magnetic field in region (4) shown in FIG. 96) is applied in the recording direction, so that the sublattice magnetic moment of the transition metal atom of the first magnetic layer A is in the erasure direction, and the transition metal atom of the second magnetic layer B is Can be directed in the recording direction.
[0021]
The magnitude of the change in the Kerr rotation angle detected as a signal from the magneto-optical recording medium is proportional to the sum of the sublattice magnetic moments of the transition metal atoms in the first magnetic layer A and the second magnetic layer B.₀ , H₁ , H₂ , H_Three The relative signal output shown in FIG. 98 (b) is obtained from the recording track to which the external magnetic field is sequentially applied. Thus, for example, as shown in FIG.₁ The recording state due to "0", external magnetic field H₀ "1" for the recording state by the external magnetic field H_Three "2" for the recording state by the external magnetic field H₂ By locating the recording state by “3”, the signal can be recorded in four values.
[0022]
In addition, a first magnetic layer having a recording state in two different magnetic field regions with respect to an applied external magnetic field, and a second magnetic layer having two recording states in a magnetic field region different from the first magnetic layer Even in the case of using a magneto-optical recording medium in which a magnetic layer is laminated, four-value recording of signals can be performed on the same principle as this. For example, when a first magnetic layer having the characteristics shown by the one-dot chain line in FIG. 99B and a second magnetic layer having the characteristics shown by the broken line in FIG. 99B are stacked, the structure shown in FIG. H₀ , H₁ , H₂ , H_Three By applying these external magnetic fields, the four recording states “0”, “1”, “2”, and “3” shown in FIG. 99B can be displayed. Thus, for example, as shown in these figures, the external magnetic field H₀ The recording state due to "0", external magnetic field H₁ "1" for the recording state by the external magnetic field H₂ "2" for the recording state by the external magnetic field H_Three By positioning the recording state by “3”, the signal can be recorded in four values with an external magnetic field of about ± 100 (Oe). In this case, as shown in FIG. 100, if a DC bias magnetic field is applied to the external magnetic field and the central magnetic field of the external magnetic field is shifted to the minus side by about −50 (Oe), it is as small as ± 50 (Oe). It also enables ternary recording of signals with an external magnetic field.
[0023]
Thus, since the magneto-optical recording medium of the present invention can perform quaternary recording of signals with two magnetic layers, it can be compared with the conventional magneto-optical recording medium that can only record ternary signals with two magnetic layers. Therefore, higher density signal recording can be realized with a simpler configuration. 96, 99, and 100, each recording state is extremely stable against fluctuations in the external magnetic field, and the magnetic characteristics of each magnetic layer, the laser beam intensity during recording and reproduction, and the external magnetic field intensity. Therefore, it is not necessary to make the subtle matching, so that a magneto-optical recording / reproducing system excellent in mass productivity and reliability can be constructed.
[0024]
Note that if the magnetic layers are laminated in two or more layers, higher-order multi-value recording according to the number of magnetic layers can be performed. Further, as a magneto-optical recording medium, magneto-optical recording in which three or more magnetic layers are stacked and at least one of the magnetic layers has a recording state in two or more different magnetic field regions with respect to an applied external magnetic field. If a film is used, multi-value recording of five or more values can be performed by making the external magnetic field strength correspond to the recording state of each magnetic layer.
[0025]
The operation of the recording / reproducing method for recording a multi-value recording signal on the magneto-optical recording medium for multi-value recording, which is larger than the number of magnetic field regions in the stable recording state of the magneto-optical recording medium, will be described below.
[0026]
The multilevel signal recorded on the magneto-optical recording medium can be divided into a plurality of signal sequences by an appropriate method. For example, a four-value recording signal (003122001203213331130230113203210) is divided by two from the beginning, so that (00) (31) (22) (00) (12) (03) (21) (33) (11) (30 ) (23) (01) (13) (20) (32) (10), and by taking out the first and second signals of each set separately, It can be divided into a first signal string (032023132012231) and a second signal string (0120231310313020).
[0027]
The recording of the first signal sequence on the quaternary recording magneto-optical recording medium can be performed by the method described above. The overwriting of the second signal train on the first signal train written on the magneto-optical recording medium is performed under the condition that the magnetization of the first write signal train can be reversed and the laser intensity and / or the external magnetic field. This is possible by setting the intensity. Further, when the second signal sequence is overwritten on the first write signal sequence, the width of the second signal sequence is made smaller than the width of the first write signal sequence (the width of the magnetization domain), It is possible to rewrite a part of one write signal sequence to the second signal sequence by adjusting the size of the laser spot. In addition, it is possible to easily synchronize the head of the first write signal string and the head of the second write signal string by using the conventional technique. Therefore, by operating the recording laser beam a plurality of times on the same track, a plurality of divided signal trains can be recorded on the same track with different widths.
[0028]
Thus, when the first signal sequence and the second signal sequence are overwritten in synchronism with the track direction on the same track with different widths, the signals of the first and second signal sequences are both “3”. ", The first signal train signal is" 3 "and the second signal train signal is" 2 ", and the first signal train signal is" 3 "and the second signal train The region where the signal is “1”, the region where the signal of the first signal sequence is “3” and the signal of the second signal sequence is “0”, and the signal of the first signal sequence is “2” and the second The signal sequence signal of “3”, the first signal sequence signal of “2”, the second signal sequence signal of “2”, and the first signal sequence signal of “2” ”In the region where the signal of the second signal sequence is“ 1 ”, the region where the signal of the first signal sequence is“ 2 ”and the signal of the second signal sequence is“ 0 ”, and The area where the signal is “1” and the signal of the second signal sequence is “3” The first signal train signal is “1” and the second signal train signal is “2”, and the first signal train signal is “1” and the second signal train signal is “1”. ", The first signal train signal is" 1 "and the second signal train signal is" 0 ", and the first signal train signal is" 0 "and the second signal train A region where the signal is “3”, a region where the signal of the first signal sequence is “0” and the signal of the second signal sequence is “2”, and a signal of the first signal sequence is “0” and the second The region where the signal sequence signal of “1” is “1” and the region where both of the first and second signal sequence signals are “0” are equal to or larger than the width of the first write signal sequence. When the reproduction laser spot is irradiated, since the total magnetization state of the areas irradiated with the reproduction laser spot is different, a 16-value recording signal can be detected. Further, if the recording signal is divided into three signal strings and these three signal strings are overwritten on the same track, 64-value signal recording can be performed by the same principle.
[0029]
Therefore, using the magneto-optical recording medium for multi-level recording according to the present invention, more advanced multi-level recording of signals can be realized, and a magneto-optical recording medium with a large amount of recorded information can be provided at low cost.
[0030]
The quaternary recording signal can be converted from the binary recording signal by the following method, for example. That is, by dividing the binary recording signal (00001101101000000110001110011111010111100101100010111100011100100) from the top by two, (00) (00) (11) (01) (10) (10) (00) (00) (01) (10) ( 00) (11) (10) (01) (11) (11) (01) (01) (11) (00) (10) (11) (00) (01) (01) (11) (10) (00) (11) (10) (01) (00) is converted into a signal sequence. Next, the signal “0” is set in the group (00), the signal “1” is set in the group (01), the signal “2” is set in the group (10), and the signal “3” is set in the group (11). By assigning, the above four-value recording signal (00312200120321331130230113203210) can be obtained.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
  First, a typical example of a multi-value recording magneto-optical recording medium according to the present invention is shown in FIG.FIG. 4, FIG. 7, FIG.This will be described with reference to FIG.
[0032]
  FIG.FIG. 4, FIG. 7, FIG.As illustrated in FIG. 8, the magneto-optical recording medium for multi-level recording according to the present invention is formed by laminating a plurality of magnetic layers having different coercive forces from each other like the known multi-level recording magneto-optical recording medium. Instead, when the temperature acting on the recording layer (magnetic layer) and the external magnetic field are changed, at a high temperature state, at least three different magnetic field strength ranges depending on the change of the applied external magnetic field. Magnetization in which the total magnetization is in a stable magnetization state, and in a low temperature state, the external magnetic field is zero, and at least three or more magnetization states exist stably depending on the magnitude of the external magnetic field applied at a high temperature. The recording layer is formed of a plurality of magnetic layers having characteristics or a combination of these and a nonmagnetic layer. In other words, as is apparent from these drawings, the recording layer is formed by a plurality of magnetic layers in a form in which the hysteresis loop is separated into three or more regions or a combination of these and a nonmagnetic layer at high temperatures. It can also be said that.
[0033]
In the magneto-optical recording medium of FIG. 3, a SiN film, an RE (rare earth) -rich TbFeCo film, an SiN film, an RE-rich TbFeCo film, and a PtCo film are sequentially laminated from the transparent substrate side (not shown). . Here, the lower TbFeCo film is the first magnetic layer, the upper TbFeCo film is the second magnetic layer, and the PtCo film is the auxiliary magnetic layer of the second magnetic layer. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (170 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ , H_Three By assigning recording states “0”, “1”, “2”, and “3” to each of these, four-value recording of signals becomes possible.
[0034]
The magneto-optical recording medium in FIG. 4 is formed by sequentially laminating a SiN film, a RE-rich TbFeCo film, a PtCo film, a TM (transition metal) -rich GdFeCo film, and a SiN film from the transparent substrate side (not shown). Yes. Here, the TbFeCo film is the first magnetic layer, the GdFeCo film is the second magnetic layer, and the PtCo film is the auxiliary magnetic layer of the first magnetic layer and the second magnetic layer. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (150 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ , H_Three By assigning recording states “0”, “1”, “2”, and “3” to each of these, four-value recording of signals becomes possible.
[0035]
  The magneto-optical recording medium of FIG.Reference example,From the transparent substrate side (not shown), an SiN film, an RE-rich TbFeCo film, a TM-rich GdTbFeCo film, an SiN film, and an Al film are sequentially stacked. Here, the TbFeCo film is a first magnetic layer, and the GdTbFeCo film is a second magnetic layer. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (180 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ , H_Three By assigning recording states “0”, “1”, “2”, and “3” to each of these, four-value recording of signals becomes possible.
[0036]
  The magneto-optical recording medium of FIG. 6 includes an SiN film, an RE-rich TbFeCo film, a Co film, an SiN film, an RE-rich TbFeCo film, a PtCo film, and an SiN film from the transparent substrate side (not shown). They are sequentially stacked. The lower TbFeCo film is the first magnetic layer, the Co film is the auxiliary magnetic layer, the upper TbFeCo film is the second magnetic layer, and the PtCo film is the auxiliary magnetic layer. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (170 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ ,H _Three ofThe recording states “0”, “1”, “2”,“3”By assigning the signal4Value recording is possible.
[0037]
The magneto-optical recording medium of FIG. 7 includes an SiN film, a TM rich TbFeCo film, an SiN film, a TM rich TbFeCo film, an RE rich GdFeCo film, and an SiN film sequentially from the transparent substrate side (not shown). Are stacked. Here, the lower TbFeCo film is the first magnetic layer, the upper TbFeCo film is the second magnetic layer, and the GdFeCo film is the auxiliary magnetic layer. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (160 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ By assigning the recording states “0”, “1”, and “2” to each of these, it is possible to record signals in three values.
[0038]
In the magneto-optical recording medium of FIG. 8, the SiN film, the RE rich TbFeCo film, the TbFeCo—O film (oxidized TbFeCo film), the TM rich TbFeCo film, and the SiN film are sequentially formed from the transparent substrate side (not shown). Are stacked. Here, the lower TbFeCo film is the first magnetic layer, the upper TbFeCo film is the second magnetic layer, and the oxidized TbFeCo film is the auxiliary magnetic layer of the first and second magnetic layers. In the magneto-optical recording medium of this example, a hysteresis loop in a high temperature state (170 ° C.) and a low temperature state (25 ° C.) has a shape as shown in the center of the figure, and a magnetization characteristic has a shape as shown on the right side of the figure. . Therefore, H₀ , H₁ , H₂ , H_Three By assigning recording states “0”, “1”, “2”, and “3” to each of these, four-value recording of signals becomes possible.
[0039]
  Note that FIG.FIG. 4, FIG. 7, FIG.As illustrated in FIG. 8, the magnetic layer material is most preferably an amorphous alloy of a rare earth and a transition metal. However, the magnetic layer material applicable to the present invention is not limited to this, and a garnet-based or ferrite-based oxide magnetic material, a noble metal such as Pt or Pd, a transition metal such as Fe or Co, and / or Tb. Other materials having a large magneto-optic effect and capable of being thinned, such as alternating laminates of rare earth metals such as PdMnSb, Heusler alloys such as PtMnSb, and MnBi, can also be used. Further, when the magnetic layer on the side irradiated with the laser beam is a metal, it is necessary to make the magnetic layer sufficiently thin so that the light beam can be sufficiently transmitted, and it is 500 mm or less, more preferably 250 mm. The following is desirable.
[0040]
Next, the multi-value recording principle of the magneto-optical recording medium according to the present invention will be described based on the hysteresis loop of FIG. FIG. 1A shows a typical hysteresis loop when the magneto-optical recording medium according to the present invention is at a low temperature (temperature range from room temperature to irradiation with a reproducing laser beam), and FIG. It is a typical hysteresis loop in (temperature range at the time of information rewriting).
[0041]
As shown in FIG. 1B, this magneto-optical recording medium is H₀', H₁', H₂', H_ThreeFor each of the four external magnetic field regions ′, the magnetization is M₀', M₁', M₂', M_ThreeIt takes one value of '. On the other hand, at low temperatures, the large hysteresis loop consists of one region. This loop is M₀ Applying an external magnetic field from the magnetized state of H_Three If the external magnetic field is reduced to 0 after reaching the size of_Three In the magnetization state of H₂ When the operation of returning the external magnetic field to 0 when the value reaches the value of 0, that is, the operation of drawing a small hysteresis loop,₂ The magnetization state of exists stably. M_Three Applying an external magnetic field in the negative direction from the magnetized state of H₀ If the external magnetic field is reduced to 0 after reaching the size of₀ In the magnetization state of H₁ When the external magnetic field is returned to zero when the magnitude of₁ The magnetization state of exists stably. In this way, in the low temperature region, the large hysteresis loop and the small hysteresis loop cause M₀, M₁, M₂, M_ThreeThese four magnetization states exist stably with zero external magnetic field. Therefore, as shown in FIG.₀ , H₁ , H₂ , H_Three By assigning recording states “0”, “1”, “2”, and “3” to each of these, four-value recording of signals becomes possible.
[0042]
Further, as is apparent from FIG. 1B, the magneto-optical recording medium is heated to a high temperature state and a stable magnetization state is obtained regardless of the magnetization state before recording a certain signal. When a predetermined external magnetic field necessary for the recording is applied, the magnetization of the recording layer becomes a magnetization state corresponding to the magnitude of the applied external magnetic field after the temperature is lowered, regardless of the history so far. Therefore, the magneto-optical recording medium of the present invention can directly write new information directly on the previously recorded information without erasing the previously recorded information.
[0043]
Since the temperature at the time of information rewriting may be set to be equal to or higher than the temperature of the reproduction laser light irradiation part, the hysteresis loop in the high temperature region is defined from the temperature of the reproduction laser light irradiation part to the Curie temperature. It may be realized at any of the temperatures. Usually, the temperature of the irradiation portion of the reproducing laser beam is 80 ° C. or higher.
[0044]
  In addition, FIG.FIG. 4, FIG. 7, FIG.Not only the magneto-optical recording medium having the film structure illustrated in FIG. 8, but also the magneto-optical recording medium having hysteresis loops at high temperatures and low temperatures as shown in FIG. 1 can perform multi-value recording of signals.
[0045]
In the following, a configuration example of a multi-value recording magneto-optical recording medium based on the above principle will be given and each will be described.
[0046]
<First configuration example>
As shown in FIG. 9A, a magneto-optical recording medium according to this example includes a substrate 1 on which a desired preformat pattern 2 is formed on one side, and a first enhancement film 3 formed on the preformat pattern 2. A first magnetic layer 4 formed on the first enhancement film 3, a second enhancement film 5 formed on the first magnetic layer 4 as necessary, and the second enhancement film 5 or the first magnetic layer. A second magnetic layer 6 formed on the fourth magnetic layer 6, a third enhancement film 7 formed on the second magnetic layer 6 as necessary, a reflection film 8 formed on the third enhancement film 7, and a reflection The protective film 9 is formed on the film 8.
[0047]
As the transparent substrate 1, for example, a transparent resin material such as polycarbonate, polymethyl methacrylate, polymethylpentene, and epoxy is formed into a desired shape, or a desired preformat pattern is formed on one side of a glass plate formed in a desired shape. Any known transparent substrate such as one in which the transparent resin layer to which 2 has been transferred is adhered can be used. Note that the configuration, arrangement, formation method, and the like of the preformat pattern 2 are matters that are publicly known and are not the gist of the present configuration example, and thus description thereof is omitted.
[0048]
The first to third enhancement films 3, 5, and 7 are provided to cause multiple interference of the reproducing light beam in the film and increase the apparent Kerr rotation angle. Is formed of an inorganic dielectric having a large refractive index. As the enhancement film material, silicon, aluminum, zirconium, titanium, tantalum oxide or nitride is particularly suitable. The first enhancement film 3 is formed to a thickness of 600 to 1200 mm. The second and third enhancement films 5 and 7 are formed as necessary, and are formed to have an arbitrary film thickness of 500 mm or less, and may be omitted in some cases.
[0049]
The reflection film 8 is provided to increase the effective Kerr rotation angle of the medium by increasing the reflectance and to adjust the recording sensitivity of the medium by adjusting the thermal conductivity. In contrast, it is made of a material having a high reflectance. Specifically, one or more metal elements selected from the group of [Al, Ag, Au, Cu, Be], [Cr, Ti, Ta, Sn, Si, Rb, Pe, Nb, Mo, Li, , Mg, W, Zr] is particularly suitable an alloy made of one or more metal elements selected from the group of [, Mg, W, Zr], and when this kind of alloy is used, it is formed to a thickness of 300 to 1000 mm.
[0050]
The protective film 9 is for protecting the film bodies 3 to 8 from mechanical impacts and chemical adverse effects, and is applied to cover the entire film body. An example of the protective layer material is a resin material. In particular, an ultraviolet curable resin is preferable because film formation is easy.
[0051]
The first magnetic layer 4 is made of a rare earth-transition metal-based amorphous alloy in which the rare earth sublattice magnetization moment is dominant in the temperature range from room temperature to the Curie temperature, or from the room temperature to the highest temperature reached at the time of recording or erasing. The amorphous perpendicular magnetization film 4a having a thickness of 100 to 500 mm and the auxiliary magnetic film 4b having a thickness of 5 to 100 mm provided in contact therewith are formed. As the rare earth-transition metal-based amorphous perpendicular magnetic film, those represented by the following general formula are particularly preferable.
[0052]

[0053]
The auxiliary magnetic film 4b is made of a magnetic material containing a transition metal element and having a small perpendicular magnetic anisotropy. As a specific example,
(1) At least one element selected from a noble metal element group such as [Pt, Al, Ag, Au, Cu, Rh] and at least selected from a transition metal element group such as [Fe, Co, Ni] Alloy thin film with one element,
(2) Rare earth-transition metal alloys with reduced perpendicular magnetic anisotropy by containing Gd or Nd, such as GdFeCo alloy, GdTbFeCo alloy, GdDyFeCo alloy, NdFeCo alloy, etc.
(3) A rare earth-transition metal alloy having reduced perpendicular magnetic anisotropy by containing a larger amount of oxygen or nitrogen (for example, 5 atomic% or more) than usual,
(4) A film in which a transition metal such as [Fe, Co, Ni] or the like, or an alloy containing a large amount thereof is laminated in a thickness of 5 to 30 mm and several atomic layers,
And so on.
[0054]
These auxiliary magnetic films 4b have perpendicular magnetic anisotropy energy that is equal to or lower than the shape anisotropy depending on the composition, and magnetization is in-plane direction (auxiliary magnetic film 4b) before an external magnetic field is applied. In a direction parallel to the film surface). When the auxiliary magnetic film 4b adjusted in this way is heated to near the Curie temperature and an external magnetic field is applied, the magnetization direction rises from the in-plane direction to generate a magnetic moment component in the external magnetic field direction. Exchange coupling force is exerted on the transition metal magnetic moment of the amorphous perpendicular magnetization film 4a laminated in contact therewith. Therefore, in the first recording layer formed by laminating the amorphous perpendicular magnetization film 4a and the auxiliary magnetic film 4b, the change in the carrier wave and noise level of the optical modulation recording signal with respect to the external magnetic field is as shown in FIG. It has two peaks.
[0055]
The second magnetic layer 6 is composed of a magneto-optical recording film in which at least one recording state exists in a magnetic field region different from that of the first magnetic layer 4. Therefore, it is possible to use an amorphous perpendicular magnetization film and auxiliary magnetic film of the same type as the first magnetic layer 4 and having two recording states in different magnetic field regions from the first magnetic layer 4. The first magnetic layer 4 may have a different configuration, and as shown in FIG. 9C, one having one recording state in a magnetic field region different from the first magnetic layer 4 may be used. . As the second magnetic layer 6 belonging to the latter, (1) from a rare earth-transition metal type amorphous perpendicular magnetic film in which transition metal sublattice magnetization is dominant in a temperature range from room temperature to the highest temperature at the time of recording and erasing. (2) Consists of a rare earth-transition metal amorphous perpendicular magnetization film in which the rare earth sublattice magnetization is dominant in the same temperature range as above, (3) Compensation temperature between room temperature and Curie temperature And those composed of a rare earth-transition metal amorphous perpendicular magnetic film in which there exists. Specifically, those represented by the following general formula are particularly preferable. The thickness of the second magnetic layer 6 is preferably formed in the range of 100 to 500 mm.
[0056]

[0057]
The film bodies 3 to 8 are sequentially laminated on the preformat pattern forming surface of the transparent substrate 1 by a vacuum film forming method such as sputtering or vacuum deposition. When each of these film bodies 3 to 8 reads a signal from a multi-value recorded optical information recording medium, the difference in the reproduction output level (the magnitude of the Kerr rotation angle) corresponding to each recording level can be as much as possible. The film thickness and optical constant are selected to be uniform. Depending on the selection at that time, the second and third enhancement films 5, 7 and / or the reflection film 8 may be omitted. Moreover, the laminated positions of the first magnetic layer 4 and the second magnetic layer 6 may be interchanged. If the stacking position of each magnetic layer is changed, the magnitude of the Kerr rotation angle in each recording state corresponding to the magnitude of the external magnetic field at the time of recording and the magnitude of the irradiated laser power will change. This is possible, and there is no change in the characteristics and effects of the magneto-optical recording medium. Further, it is possible to perform higher-order multilevel recording by laminating magnetic layers in three or more layers, and the composition of each film can be appropriately changed accordingly.
[0058]
Examples of the magneto-optical recording medium belonging to this example will be illustrated below.
[0059]
<First embodiment>
As shown in FIG. 10, the magneto-optical recording medium of this example has a 100 nm thick SiN film and a 15 nm thick Tb on the preformat pattern forming surface 2 of the transparent substrate 1.₁₉Fe₆₂Co_TenCr₉ A film, a 10 nm thick SiN film, and a 20 nm thick Tb₃₂Fe₅₆Co₁₂Film and Pt with a film thickness of 5 nm₈₀Co₂₀A film, a SiN film having a thickness of 10 nm, and an Al film having a thickness of 70 nm are sequentially stacked, and each of these films is covered with an ultraviolet curable resin film.
[0060]
The SiN film having a thickness of 100 nm constitutes the first dielectric layer 3, and the two SiN films having a thickness of 10 nm constitute the second and third dielectric layers 5 and 7, respectively. Tb₁₉Fe₆₂Co_TenThe film constitutes the first magnetic layer 4 as a single layer, and one recording state exists in a specific magnetic field region. Tb stacked directly on top of each other₃₂Fe₅₆Co₁₂Membrane and Pt₈₀Co₂₀The film forms the second magnetic layer 6, and two recording states exist in a magnetic field region different from that of the first magnetic layer 4. Further, the Al film constitutes the reflective film 8, and the ultraviolet curable resin film constitutes the protective film 9.
[0061]
<Second embodiment>
As shown in FIG. 11, the magneto-optical recording medium of this example has a SiN film having a thickness of 100 nm and a Tb having a thickness of 15 nm on the preformat pattern forming surface 2 of the transparent substrate 1.₃₂Fe₅₆Co₁₂Film and Gd with a film thickness of 2 nm₁₈Fe₆₇Co₁₅A film, a 10 nm thick SiN film, and a 20 nm thick Tb₁₉Fe₆₂Co_TenCr₉A film, a SiN film having a thickness of 10 nm, and an Al film having a thickness of 70 nm are sequentially stacked, and each of these films is covered with an ultraviolet curable resin film.
[0062]
  Tb stacked directly on top of each other₃₂Fe₅₆Co₁₂Membrane and Gd₁₈Fe₆₇Co₁₅The film constitutes the first magnetic layer 4, and two recording states exist in different magnetic field regions. Tb₁₉Fe₆₂Co_TenThe film forms the second magnetic layer 6 as a single layer, and one recording state exists in a magnetic field region different from that of the first magnetic layer 4. The magneto-optical recording medium of this example is the first1Example magneto-optical recordingMediumUnlike the first embodiment, the first magnetic layer 4 provided on the side close to the substrate 1, that is, on the incident side of the recording / reproducing laser beam, is composed of a laminate of two magnetic films. Therefore, for the purpose of not reducing the incident amount of the laser beam to the second magnetic layer 6, a GdFeCo film having a low laser beam absorptance is used as the auxiliary magnetic film constituting the first magnetic layer 4, and the film thickness thereof is used. Was made as thin as 2 nm. Since the other parts are the same as those in the first embodiment, the corresponding parts are denoted by the same reference numerals and the description thereof is omitted.
[0063]
<Third embodiment>
As shown in FIG. 12, the magneto-optical recording medium of this example has a 100 nm thick SiN film and a 15 nm thick Tb on the preformat pattern forming surface 2 of the transparent substrate 1.₃₂Fe₅₆Co₁₂A film and a (Tb₃₂Fe₅₆Co₁₂)₉₂O₈ A film, a 10 nm thick SiN film, and a 20 nm thick Tb₁₉Fe₆₂Co_TenCr₉A film, a SiN film having a thickness of 10 nm, and an Al film having a thickness of 70 nm are sequentially stacked, and each of these films is covered with an ultraviolet curable resin film.
[0064]
Tb stacked directly on top of each other₃₂Fe₅₆Co₁₂(Tb₃₂Fe₅₆Co₁₂)₉₂O₈ The film constitutes the first magnetic layer 4, and two recording states exist in different magnetic field regions. Tb₁₉Fe₆₂Co_TenThe film forms the second magnetic layer 6 as a single layer, and one recording state exists in a magnetic field region different from that of the first magnetic layer 4. The magneto-optical recording medium of this example has a low laser beam absorptivity as an auxiliary magnetic film constituting the first magnetic layer 4 for the purpose of not reducing the amount of laser beam incident on the second magnetic layer 6 (Tb₃₂Fe₅₆Co₁₂)₉₂O₈ While using the film, the film thickness was adjusted to 7 nm. Since the other parts are the same as those in the first embodiment, the corresponding parts are denoted by the same reference numerals and the description thereof is omitted.
[0065]
<Fourth embodiment>
As shown in FIG. 13, the magneto-optical recording medium of this example has a 100 nm thick SiN film and a 15 nm thick Tb on the preformat pattern forming surface 2 of the transparent substrate 1.₃₂Fe₅₆Co₁₂Film and Gd with a film thickness of 2 nm₃₀Fe₄₈Co_{twenty two}A film, a 10 nm thick SiN film, and a 20 nm thick Tb₃₄Fe₅₂Co₁₄Film and Pt with a film thickness of 5 nm₉₄Co₆A film, a SiN film having a thickness of 10 nm, and an Al film having a thickness of 70 nm are sequentially stacked, and each of these films is covered with an ultraviolet curable resin film.
[0066]
Tb stacked directly on top of each other₃₂Fe₅₆Co₁₂Membrane and Gd₃₀Fe₄₈Co_{twenty two}The film constitutes the first magnetic layer 4, and two recording states exist in different magnetic field regions. Also, Tb directly stacked on each other₃₄Fe₅₂Co₁₄Membrane and Pt₉₄Co₆The film forms the second magnetic layer 6, and two recording states exist in a magnetic field region different from that of the first magnetic layer 4. The magneto-optical recording medium of this example is a GdFeCo film having a low laser beam absorptivity as an auxiliary magnetic film constituting the first magnetic layer 4 for the purpose of not reducing the amount of laser beam incident on the second magnetic layer 6. And the film thickness was adjusted to 2 nm. Since the other parts are the same as those in the first embodiment, the corresponding parts are denoted by the same reference numerals and the description thereof is omitted.
[0067]
<Second configuration example>
The magneto-optical recording medium according to the present embodiment is characterized in that a film body for realizing so-called magnetic super-resolution is added to the multi-value recording magneto-optical recording medium as exemplified in the first configuration example. .
[0068]
  FIG.4Is a block diagram showing an example of the two,Magnetic layerThis shows a case where the present invention is applied to a magneto-optical recording medium for multilevel recording. As is clear from this figure, the magneto-optical recording medium of this example has a first dielectric layer 101, a first aperture forming layer 102, a first cutting layer 103, and a first layer on a transparent substrate 1. The perpendicular magnetic film layer 104, the first auxiliary magnetic layer 105, the second dielectric layer 106, the second aperture forming layer 107, the second cutting layer 108, the second perpendicular magnetic film layer 109, In principle, the auxiliary magnetic layer 110, the third dielectric layer 111, and the reflective layer 112 are formed. The first magnetic layer 120 is configured by a combination of the first perpendicular magnetic film layer 104 and the first auxiliary magnetic layer 105, and the second magnetic layer 121 includes the second perpendicular magnetic film layer 109, the second auxiliary magnetic layer 110, and the like. Consists of a combination of
[0069]
The first aperture forming layer 102, the first cutting layer 103, and the first magnetic layer 120 are configured by magnetic films that are exchange-coupled magnetically with each other at room temperature, and in this order with respect to the incident direction of the reproducing laser beam. Laminated. These magnetic films 102, 103, and 120 have the Curie temperature of the first aperture forming layer 102 Tc₁ , Its coercive force is Hc₁ , The Curie temperature of the first cutting layer 103 is Tc₂ , Its coercive force is Hc₂ The Curie temperature of the first magnetic layer 120 is Tc_Three , Its coercive force is Hc_Three And the room temperature is T₀ The exchange magnetic field exerted on the first aperture forming layer 102 by the first cutting layer 103 and the first magnetic layer 120 is H._w , An external magnetic field applied during reproduction (hereinafter referred to as a reproduction magnetic field) is H_r Then, the Curie temperature and the coercive force are adjusted so as to satisfy the following conditions (1) to (4).
▲ 1 ▼ T₀ <Tc₂ <Tc₁ , Tc_Three
▲ 2 ▼ Hc₁ + H_w <H_r
(However, the Curie temperature Tc of the first cutting layer 103 during reproduction is₂ Or in the region where the temperature rises to the vicinity)
(3) Hc_Three > H_r
(However, the Curie temperature Tc of the first cutting layer 103 during reproduction is₂ Or in the region where the temperature rises to the vicinity)
▲ 4 ▼ Hc₁ <H_w
(However, at room temperature).
[0070]
The second hole forming layer 107, the second cutting layer 108, and the second recording layer 121 are configured in the same manner.
[0071]
Hereinafter, the principle of reproducing a signal from the magneto-optical recording medium configured as described above will be described with reference to FIG. In the magneto-optical recording medium, as shown in FIG. 15A, recording marks 120 a and 121 a having a diameter smaller than the spot diameter D of the reproducing light beam 130 are spotted on the reproducing light beam 130 along the recording track. It is recorded at a pitch smaller than the diameter D.
[0072]
When the magneto-optical recording medium is irradiated with the reproducing light beam 130 while the magneto-optical recording medium is driven relative to the optical head and the magnetic head, the first hole forming layer 102 and the first cutting layer are generated by the energy. 103, the first magnetic layer 120, the second aperture forming layer 107, the second cut layer 108, and the second magnetic layer 121 are heated, but the recording track is driven while driving the magneto-optical recording medium in the direction of arrow A. When the reproduction light beam 130 is radiated along, the rear edge portion of the spot 131 becomes the highest temperature as shown in FIG. 15B due to the temperature distribution in the irradiation portion of the reproduction light beam 130 that travels relatively. Become. Therefore, the intensity of the reproducing light beam 130 is set so that the temperature of the high temperature region 131a is the Curie temperature Tc of the first and second cutting layers 103 and 108.₂ When adjusted to be above or in the vicinity thereof, the exchange magnetic field H exerted by the cut layers 103 and 108 and the magnetic layers 120 and 121 on the hole forming layers 102 and 107 is as follows._w Becomes zero or a very small value, and the magnetic coupling between the hole forming layers 102 and 107 and the magnetic layers 120 and 121 is cut off.
[0073]
In this state, Hc₁ + H_w Larger reproducing magnetic field H_r Is applied to each magnetic film, as shown in FIG. 15 (a), the magnetization of the portion corresponding to the high temperature region 131a of the hole forming layers 102 and 107 is aligned in the direction of the reproducing magnetic field, and the hole forming in that region is formed. The recording marks 120a and 121a on the layers 102 and 107 disappear. On the other hand, in a portion other than the high temperature region 131a, the exchange magnetic field H_w Maintains a large value, and the hole forming layers 102 and 107 and the magnetic layers 120 and 121 are magnetically coupled, so that the recording marks 120a, 121a is kept as it is. Therefore, when the reproducing light beam 130 is operated along the recording track, the recording marks 120a and 121a in the high temperature region 131a are masked for signal readout, and only the crescent-shaped portion of the spot 131 excluding the high temperature region 131a is masked. Becomes an aperture, and signals from the recording marks 120a and 121a are read out. Therefore, it is possible to read a signal from the magneto-optical recording medium in which the magnetic section pitch is adjusted to about ½ of the spot diameter D, and the reproduction resolution is improved.
[0074]
The coercive force Hc of the magnetic layers 120 and 121_Three Is the reproducing magnetic field H_r Is set larger than the reproducing magnetic field H_r Does not erase the recording marks 120a and 121a of the magnetic layers 120 and 121. In addition, the portion removed from the irradiation portion of the reproducing light beam 130 with the driving of the magneto-optical recording medium is sequentially cooled to room temperature, and the temperature of the cutting layers 103 and 108 is Tc.₂ Once cooled to the following, the exchange magnetic field H is again between the magnetic films._w Will be resurrected. Therefore, the reversal magnetic domains of the magnetic layers 120 and 121 are transferred to the aperture forming layers 102 and 107 by the exchange coupling force, so that the original recording state is not lost even if the signal reproducing operation is repeated. Therefore, as shown in FIG. 15C, the read-out total reproduction signal is sliced with a plurality of slice signals matching each signal level, thereby reproducing the multi-value recorded signal with high resolution. be able to.
[0075]
FIG. 16 shows another example of the multilevel recording signal reproduction method using the magnetic super-resolution method. Unlike the method of FIG. 15, the reproducing method of this example is characterized in that an initialization magnetic field is applied to the aperture forming layers 102 and 107 on the upstream side of the optical head, and an aperture is formed in the high temperature portion 131a. .
[0076]
For magneto-optical recording media having a plurality of aperture forming layers, the exchange coupling forces acting between the magnetic layers and the aperture forming layers may be different from each other, or the curie of each aperture forming layer may be By making the temperatures different from each other, the reproduction signal can be read out for each magnetic layer. That is, the opening portion at the time of reproducing light irradiation is larger in the first magnetic layer 120 near the reproducing light incident side. Therefore, in the magneto-optical recording medium in which the aperture is formed in the high temperature portion 131a, the exchange coupling force acting between the first magnetic layer 120 and the first aperture portion forming layer 102 is changed to the second magnetic layer 121 and the second aperture. It is stronger than the exchange coupling force acting between the hole forming layer 107 or the Curie temperature of the first hole forming layer 102 is set lower than the Curie temperature of the second hole forming layer 107, Then, an appropriate two-power reproducing laser beam is selected and, as shown in FIG. 17, the magneto-optical recording medium is irradiated with a low-power reproducing laser beam that does not have an opening in the second magnetic layer. A signal can be reproduced only from the first magnetic layer 120. Further, as shown in FIG. 18, only the second magnetic layer is obtained by irradiating the magneto-optical recording medium with a high-power reproducing laser beam in which the aperture of the first recording layer covers almost the entire area of the reproducing spot. The signal can be reproduced from
[0077]
In the magneto-optical recording medium in which the aperture is formed in the low temperature portion of the reproduction spot, the exchange coupling force acting between the first magnetic layer 120 and the first aperture portion forming layer 102 is caused to exchange with the second magnetic layer 121 and the second aperture. The exchange coupling force acting with the hole forming layer 107 is made weaker or the Curie temperature of the first hole forming layer 102 is set higher than the Curie temperature of the second hole forming layer 107. Thus, a signal can be selectively reproduced from the first or second magnetic layer.
[0078]
Note that the magneto-optical recording medium for multi-value recording of the magnetic super-resolution system does not necessarily include all the film bodies shown in FIG. 14, and one or a plurality of film bodies can be omitted as necessary. . FIG. 19 shows various film configurations included in the fourth configuration example. The blank in the table indicates that the film body is omitted.
[0079]
In the first and second configuration examples, the SiN film is used as the dielectric layer, but other materials may be used. That is, as the dielectric layer material, non-magnetic and high thermal conductivity materials are used so that the temperature distributions during recording of the first and second magnetic layers are made as equal as possible and the sizes of the magnetic domains formed are made uniform. good. As a material suitable for this, a metal element selected from the group of [Si, Al, Ti, Zr, Au, Cu, Mo, W] or at least one metal element selected from these as a main component is used. Alloys, or their oxides or nitrides, materials whose composition is richer in metal elements than in the stoichiometric composition are particularly suitable. The film thickness of each dielectric layer is appropriately adjusted so as to satisfy the optical conditions.
[0080]
In addition, the Curie temperatures of the respective perpendicular magnetization films in the first and second configuration examples need to be close to each other in order to make the sizes of the magnetic domains formed in the respective recording layers uniform, and the maximum is ± 50. It is preferable that the temperature is set within a degree.
[0081]
In addition, the compositions of the perpendicular magnetization films in the first and second configuration examples are preferably the same in order to facilitate film formation. The auxiliary magnetic film is preferably a magnetic thin film that becomes an in-plane magnetization film at least near room temperature. Furthermore, the auxiliary magnetic film can be provided not only on one surface of the perpendicular magnetization film but also on the laser beam incident side, the opposite side, or both.
[0082]
The following is a list of high-density recording methods for magneto-optical recording media and recording / reproducing methods with few errors from high-density recording media on which fine recording magnetic domains are formed.
[0083]
(1) Pulse regeneration
a. A magneto-optical reproduction system that irradiates a reproduction laser beam periodically or in pulses.
[0084]
b. A. In this signal reproduction method, the light emission timing of the reproduction laser light is synchronized by creating a timing clock from a signal reproduced from a medium such as a pre-pit or a magneto-optical signal.
[0085]
(2) Pulse recovery waveform equalization
c. A. D₀A method of performing signal processing represented by the following equation 1 when (t).
[0086]
[Expression 1]

[0087]
d. C. N = 0, ± 1, ± 2, a_n= A_-n, -1 <a_nA method of performing signal processing <0.
[0088]
(3) Magnetic field modulation reproduction
e. A method of reproducing from a medium capable of magnetic super-resolution by modulating the magnitude and / or direction of the external magnetic field to be applied.
[0089]
f. A. Wherein the magnitude and / or direction of the external magnetic field to be applied is modulated in synchronization with the light emission timing of the reproducing laser beam. Playback method.
[0090]
g. A recording / reproducing system in which a plurality of recording pits exist in a reproducing light spot in a laser traveling direction or a cross track direction, and each level of a reproducing signal generated by each combination of recording states is determined in multiple stages.
[0091]
(4) Trial reading
h. A. ~ G. In this method, reproduction is performed by changing the waveform of the laser beam for reproduction (each value of high power and low power, the ratio of time between high power and low power) and the magnetic field applied during reproduction, and the combination with the least error is achieved. The playback method to select.
[0092]
i. Said h. In this reproduction method, a test pattern for reproduction trial is recorded in advance on a medium.
[0093]
j. Said h. The optimal playback conditions obtained by the above method are recorded on a medium, and from the next playback, it is read and played back.
[0094]
Next, the format configuration of the magneto-optical recording medium according to the present invention will be described.
[0095]
<First example of format configuration>
FIG. 20 shows an example of a preformat pattern formed on a sample servo type magneto-optical recording medium. The preformat pattern 2 defines a recording track and a data recording unit obtained by dividing the recording track. The preformat pattern 2 can be recorded on the surface of the transparent substrate 1 in a concavo-convex shape. It can also be recorded as a magneto-optical signal.
[0096]
In this example, the recording track 11 is divided into a number of data recording units 12, and each data recording unit 12 is divided into an ID area 13, a servo area 14, and a data area 15. In the ID area 13, a mark indicating the boundary of each data recording unit 12, an address of the data recording unit, an error detection code, and the like are formed. As shown in FIG. 21, the servo area 14 includes a tracking pit 16 for scanning a recording or reproducing laser beam along the recording track 11, a test area 17 for performing optimum recording and reproduction, a signal Embedded clock pits 18 necessary for drawing a reference clock necessary for recording / reproduction of the image data are formed. In the test area 17, a test signal (level detection pit) 17 a for setting the slice level of each signal included in the multilevel recording signal recorded in the recording area 14 and / or multilevel recording, if necessary. A test signal (timing for detecting timing) 17b for generating a timing signal that is a reference for detecting the edge of the signal is recorded. In addition, a multilevel recording signal is recorded in the data area 15 as a magneto-optical recording signal.
[0097]
Instead of the configuration in which the tracking pits 16 are provided in the servo area 14, a guide groove for guiding a recording or reproducing laser beam along the recording track 11 can be formed in the transparent substrate 1.
[0098]
Also, pre-pits (phase pits) formed on the surface of the transparent substrate, for example, in the form of irregularities, can be subjected to multi-value recording corresponding to the medium. Pre-pit multi-value can be realized by modulating the length, width and depth of the pre-pits, the amount of deviation of the pre-pit position in the direction perpendicular to the track direction, or a combination thereof.
[0099]
<Second example of format configuration>
The format configuration of this example is characterized in that a test area for detecting an optimum recording condition is provided in an area other than a user area where a user accesses to record, reproduce, and erase a signal. FIG. 22 is a diagram showing an embodiment applied to an optical disk of the CAV (constant angular velocity) system, in which test areas 22 are provided on the innermost and outermost circumferences of the disk via a user area 21. Yes. Note that the test area 22 can be provided only in either the innermost or outermost part of the disk. FIG. 23 is a diagram showing an embodiment applied to a ZCAV (Zoned-CAV) type optical disc, in which a test area 22 is provided in the vicinity of a zone boundary. Also in the ZCAV type optical disc, the test areas 22 can be provided in the innermost and outermost peripheral portions of the disc, similarly to the CAV type optical disc.
[0100]
Since the format configuration of each data recording unit in the user area is the same as that described in the first example, the description is omitted to avoid duplication.
[0101]
A signal multi-value recording method using the magneto-optical recording medium according to the present invention will be described below.
[0102]
<First example of multi-value recording method>
The multi-level recording method of this example is characterized in that a multi-level recording signal encoded using a so-called trellis encoding modulation system is recorded. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example (the magneto-optical recording medium of FIGS. 9 to 13) can be used.
[0103]
As shown in FIG. 24, the magneto-optical recording medium is driven in the same manner as in the first example, and the optical head and the magnetic head are positioned on predetermined tracks, and then four-value recording corresponding to a four-phase quadrature modulation trellis code is performed. Encoding is performed with a convolutional encoder. FIG. 25A shows the X when the data is input to the convolutional encoder of FIG.₁ , X₂ Shows the state. On the other hand, as described above, the magneto-optical recording medium of FIG. 9 has signal characteristics with respect to an external magnetic field as shown in FIG. Therefore, the X shown in FIG.₁ , X₂ X so that signal amplitudes are assigned in the order₁, X₂The applied magnetic field strength is set to H using₀ ~ H_Three In addition, the intensity-modulated quaternary external magnetic field is applied to the optical information recording medium in synchronization with the recording clock. Then, after the external magnetic field is switched to a predetermined value, a light pulse is irradiated from the optical head, and each recording layer of the light pulse irradiation section is heated to a temperature at which magnetization can be reversed by the external magnetic field. As a result, a magnetized domain corresponding to the magnitude of the external magnetic field is formed in the irradiation portion of each light pulse. In this case, a constant intensity laser beam may be continuously irradiated while modulating the external magnetic field.
[0104]
FIG. 26 shows a configuration example of the recording / reproducing system of the present embodiment. In this embodiment, the reproduction light is IV converted and then passed through an analog waveform equalizer to remove optical intersymbol interference, and the analog signal is A / D converted. Thereafter, the digital transversal filter absorbed the difference between the inner and outer peripheral characteristics to determine four values, and supplied to the Viterbi decoder to binarize. The recovered clock was generated from the signal after A / D conversion.
[0105]
<Second example of multi-value recording method>
The multilevel recording method of this example is characterized in that the external magnetic field is modulated in four steps according to the recording signal, and the recording laser beam is modulated in a pulse shape. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example (the magneto-optical recording medium of FIGS. 9 to 13) is used.
[0106]
First, a magneto-optical recording medium is mounted on a medium driving unit such as a turntable, an optical head is disposed on the transparent substrate side, and a magnetic head is disposed on the protective film side. The medium drive unit is activated to relatively drive the magneto-optical recording medium, the optical head, and the magnetic head at a predetermined linear velocity, and position the optical head and the magnetic head on a predetermined track.
[0107]
Thereafter, as shown in FIG. 27A, the applied magnetic field strength is H according to the recording signal from the magnetic head.₀ ~ H_Three An external magnetic field that is signal-modulated into four values and synchronized with the recording clock is applied to the optical information recording medium. Then, after the external magnetic field is switched to a predetermined value, the optical head irradiates the light pulse shown in FIG. 27B, and heats each recording layer of the light pulse irradiation section to a temperature at which magnetization can be reversed by the external magnetic field. . As a result, the magnetization domain shown in FIG. 27C corresponding to the magnitude of the external magnetic field is formed in the irradiated portion of each light pulse.
[0108]
In FIG. 27 (c), the magnetization states of the respective magnetization domains recorded in four values are identified by a right-downward oblique line, a left-downward oblique line, a vertical line, and a white background, respectively. The white background indicates that the combination of the magnetization directions of the respective perpendicular magnetization films constituting the magneto-optical recording medium of the third configuration example is in the state “0” in FIG. ) State "1". Further, the diagonally downward slanting line represents the state “2” in FIG. 31A, and the vertical line represents the state “3” in FIG.
[0109]
The signal modulation of the magnetic field strength can be performed by the method of FIG. 28 and the signal modulation circuit of FIG. 29 or FIG. Note that the circuit shown in FIG. 32 can be used as the magnetic head drive circuit of FIGS. That is, by taking the logical product of the recording clock (1) and the data signal (Sig. 1) (2) shown in the timing chart of FIG. 27 (e), the odd data (Sig. 2) (3) is obtained. Is generated. Further, the even data (Sig. 3) (4) is generated by taking the logical product of the signal obtained by inverting the recording clock (1) and the data signal (2). The length of the odd data signal is doubled by taking the logical sum of the signal obtained by delaying the odd data (3) by 1/2 clock using the shift register and the original odd data (3). Generated signal (5). Similarly, the signal (6) is generated from the even data (4). These signals (5) and (6) are connected to an amplifier G having different gains.₁ , G₂ Amplify each and add them. Next, this added signal is subjected to voltage-current conversion by a magnetic head drive circuit, so that an external magnetic field shown in FIG. 28B is applied from the magnetic head.
[0110]
In the circuit of FIG. 30, the recording signal is separated into even bits and odd bits, subjected to waveform processing such as timing adjustment and pulse length adjustment, and then amplified by amplifiers G having the same gain. Next, each amplified signal is subjected to voltage-current conversion by a separate magnetic head driving circuit, and an external magnetic field shown in FIG. 28B is applied from a magnetic head having a plurality of windings.
[0111]
Of course, other magnetic field generators such as electromagnetic coils can be used instead of the magnetic head. Furthermore, two magnetic heads having one winding can be arranged close to each other, and an external magnetic field shown in FIG. 28B can be applied from each of these magnetic heads.
[0112]
The recording state of the magnetization domain corresponding to the magnitude of each external magnetic field is as shown in FIG. Therefore, the reproduction signal read from the magnetization domain sequence is as shown in FIG. When this reproduced signal is sliced at three slice levels set to predetermined values according to the reproduced signal output from each recording state, the recorded signal can be demodulated as shown in the timing chart of FIG. Specifically, when the analog reproduction signal of FIG. 27D is binarized at slice level 1, sig. 1 is obtained. Similarly, sig. 2 is obtained, and sig. 3 is obtained. The odd data signal {circle over (5)} in FIG. 2 and sig. 3 and the sig. 1 and the sig. 1 clock signal (1) and sig. It is obtained by taking the logical product of three. The data signal can be demodulated by taking the logical sum of the signal (7) obtained by delaying the even data signal (6) by 1/2 clock and the signal (5). FIG. 33 shows a block diagram of the signal reproduction circuit.
[0113]
By performing quaternary recording by the above method, the recording linear density can be doubled as compared with the case of performing mark edge recording using a normal binary recording medium. FIG. 34 shows a comparison between the binary edge mark edge recording and the quaternary recording state when the same information is recorded with the same minimum recording domain size. As shown in this figure, according to the quaternary recording of the present invention, the linear recording density can be doubled as compared with the mark edge recording of the binary recording.
[0114]
<Third example of multi-value recording method>
In the multi-value recording method of this example, a magnetic head (electromagnetic coil) is driven at a constant frequency equal to or an integral multiple of the detection window width T, and an external magnetic field is applied to the magneto-optical recording medium, while laser irradiation is performed. It is characterized by modulating timing. FIG. 35 is a block diagram of a laser irradiation timing modulation circuit applied to the multilevel recording of this example, and FIG. 36 is a timing chart of signals handled in each part of the circuit. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example (the magneto-optical recording medium of FIGS. 9 to 13) was used.
[0115]
In the multilevel recording method of this example, in synchronization with the change of the external magnetic field, the recording laser pulse is irradiated once in one period, and each recording layer is heated to a temperature at which the coercive force becomes sufficiently small. Both or one of the magnetization of the first recording layer and the magnetization of the second recording layer is selectively reversed. The state in which the magnetization is reversed is distinguished by shifting the timing of irradiating the recording laser pulse. That is, as shown in FIG. 36, four pulse trains pulse1, pulse2, pulse3, and pulse4 that are shifted in timing are generated, and logical operation is performed on the even bit and odd bit signals separated from the recording signal Data, and each recording state is obtained. A recording laser drive pulse corresponding to is generated.
[0116]
FIG. 37 shows a block diagram of a signal reproduction circuit, and FIG. 38 shows a signal reproduction system. The reproduction signal read from the magnetized domain sequence is sliced at three slice levels set to predetermined values, and three binary signals sig1, sig2, and sig3 obtained thereby are the same as in the case of the first example. The recorded signal can be played back by the following procedure.
[0117]
<Fourth example of multi-value recording method>
In the multi-value recording method of this example, the magnetic head (electromagnetic coil) is driven at a constant frequency equal to or an integral multiple of the detection window width T, and an external magnetic field is applied to the magneto-optical recording medium while being irradiated. It is characterized by modulating the intensity of the laser. FIG. 39 shows a block diagram of a laser intensity modulation circuit applied to the multilevel recording of this example, and FIG. 40 shows a timing chart of signals handled in each part of the circuit.
[0118]
FIG. 41 shows a block diagram of a signal reproduction circuit, and FIG. 42 shows a signal reproduction method. The reproduction signal read from the magnetized domain sequence is sliced at three slice levels set to predetermined values, and three binary signals sig1, sig2, and sig3 obtained thereby are the same as in the second example. The recorded signal can be played back by the following procedure.
[0119]
<Fifth example of multi-value recording method>
The multilevel recording method of this example applies a recording signal to a desired recording track of the magneto-optical recording medium while applying an external magnetic field whose applied magnetic field strength is signal-modulated in multiple steps according to the recording signal to the magneto-optical recording medium. According to the method, a multi-value signal is recorded on a magneto-optical recording medium by irradiating a laser beam whose laser intensity is signal-modulated in multiple stages. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example can be applied.
[0120]
Even when a specific signal is recorded on a magneto-optical recording medium having specific magnetization characteristics, various combinations of the applied magnetic field intensity H and the irradiation laser intensity P are conceivable. For example, when recording the magnetic domain row in FIG. 43 (d) on the magneto-optical recording medium having the magnetization characteristics shown in FIG. 43 (a), the external magnetic field H is switched in four stages as shown in FIG. H in descending order of external magnetic field strength₀, H₁, H₂, H_ThreeIn addition, as shown in FIG. 43 (c), the irradiation laser intensity P is switched in four steps, and the irradiation laser intensity P in order from the lowest level is changed to P.₂, P_Three, P₀, P₁And (H₀, P₀) Is assigned to signal “0” and (H₁, P₁) Is assigned to signal “1” and (H₂, P₂) Is assigned to signal “2” and (H_Three, P_Three) Is assigned to the signal “3”, and the applied magnetic field intensity H and irradiation laser intensity P are driven in the patterns of FIGS. 43B and 43C, the magnetic domain sequence of FIG. 43D can be recorded.
[0121]
Also, as shown in FIG. 44 (b), the external magnetic field H is switched in four steps, and the -H is sequentially applied from the lowest external magnetic field strength.₁ , -H₀ , H₀ , H₁ In addition, as shown in FIG. 44 (c), the irradiation laser intensity P is switched in two steps, and the low level irradiation laser intensity is changed to P.₁, High level irradiation laser intensity P₀And (-H₁, P₁) Is assigned to signal “0” and (−H₀, P₀) Is assigned to signal “1” and (H₀, P₀) Is assigned to signal “2” and (H₁, P₁) Is assigned to the signal “3”, and the applied magnetic field intensity H and irradiation laser intensity P are driven in the patterns of FIGS. 44B and 44C, as shown in FIG. The same magnetic domain sequence as 43 (d) can be recorded.
[0122]
Further, as shown in FIG. 45 (b), the external magnetic field H is switched in two stages, and the low level external magnetic field intensity is reduced to -H.₀ , High level external magnetic field strength₀ In addition, as shown in FIG. 45 (c), the irradiation laser intensity P is switched between two levels, and the low level irradiation laser intensity is changed to P.₁, High level irradiation laser intensity P₀And (-H₀, P₁) Is assigned to signal “0” and (−H₀, P₀) Is assigned to signal “1” and (H₀, P₀) Is assigned to signal “2” and (H₀, P₁) Is assigned to the signal “3”, and the applied magnetic field intensity H and irradiation laser intensity P are driven in the patterns of FIGS. 63B and 63C, as shown in FIG. The same magnetic domain sequence as 43 (d) can be recorded.
[0123]
<Sixth example of multi-value recording method>
The multi-level recording method of this example does not record the multi-level recording signal on the magneto-optical recording medium in the order of the signals, but the multi-level recording signal records a specific magnetization state on the magneto-optical recording medium and / or It divides | segments into the combination of irradiation laser, and records the signal for every combination sequentially, It is characterized by the above-mentioned. As the magnetic field variable, the magnitude of the magnetic field, the modulation amplitude range, the modulation frequency, or a combination thereof can be used. As the irradiation laser variable, the laser intensity, the modulation frequency, the pulse width, or a combination thereof can be used. Can be used. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example can be applied.
[0124]
Taking the magneto-optical recording medium having the magnetization characteristics shown in FIG. 46 as an example, the multi-value recording method of this example will be described.
[0125]
FIG. 47 shows a first example. First, in the first recording, the optical head is positioned on a desired track, and H₀ The entire track is brought into a state “0” by irradiating with a laser beam having a constant intensity under the magnetic field. Next, the optical head is positioned again on the track where the first recording is performed, and H₁ A laser beam is radiated at a position corresponding to data “1” under the magnetic field to form a recording magnetic domain of state “1” in state “0”. In the third recording, the optical head is positioned again on the track on which the first and second recordings have been performed.₂ The laser beam is irradiated at a position corresponding to the data “2” under the magnetic field to form a recording magnetic domain of the state “2” in the states “0” and “1”. At this time, the signal is modulated in advance so that the recording magnetic domain in the state “2” is not formed on the recording magnetic domain in the state “1”. Similarly, in the fourth recording, the optical head is positioned again on the track on which the first to third recording is performed, and H_Three A laser beam is irradiated at a position corresponding to the data “3” under the magnetic field to form a recording magnetic domain of the state “3” in the states “0”, “1”, and “2”. According to this method, it is not necessary to switch the four values of the external magnetic field at high speed, so that the burden on the recording / reproducing apparatus can be reduced.
[0126]
FIG. 48 shows a second example of signal recording of this method. The first recording is performed by applying an external magnetic field H after positioning the optical head on a desired track.₀And H₁This is performed by irradiating the laser beam with a pulse at a position corresponding to the data “0” and “1” while switching between the two values. Next, the optical head is positioned again on the track where the first recording is performed, and the external magnetic field to be applied is H₂And H_ThreeThis is performed by irradiating the laser beam with a pulse at a position corresponding to the data “2” and “3” while switching between the two values. Thereby, the four-value recording is completed. According to this method, the external magnetic field is changed to H.₀To H_ThreeThere is no need to switch at high speed with a large amplitude up to₀~ H₁And H₂~ H_ThreeTherefore, the burden on the recording / reproducing apparatus can be reduced.
[0127]
In the previous example, each recording was repeated for each track, but the same recording method can be applied for each zone or for the entire disk.
[0128]
H₂, H_ThreeEach -H₁, -H₀For example by a double coil head, while H₀~ H₁H or H₂~ H_ThreeGenerate a magnetic field corresponding to the modulation amplitude between, and (H₀-H₁) / 2 constant magnetic field is generated as a bias, and the + and-are switched and superimposed, thereby generating H₀~ H₁H or H₂~ H_ThreeA corresponding modulation magnetic field can be applied between them.
[0129]
<Seventh example of multi-value recording method>
The multilevel recording method of this example is characterized in that a test signal for setting a slice level for discriminating signals is recorded on a magneto-optical recording medium in order to accurately determine the multilevel signal level. A magneto-optical recording medium having the format shown in FIGS. 20 and 21 is used.
[0130]
That is, the magneto-optical recording medium is driven in the same manner as in the first example of the multi-value recording method, the optical head is positioned at a track having a desired address, and the magnetic head is positioned in the vicinity of the desired track. While applying an external magnetic field according to recording data from the head, a laser beam is irradiated from the optical head to record a multilevel signal according to the external magnetic field. At this time, a test signal for setting a slice level for discriminating the recorded multilevel signal is recorded in the test area 17 of FIG. 20, and the signal is reproduced to enable the slice level to be set.
[0131]
As shown in FIG. 29, the data pattern of the test signal has at least one multi-level signal level. The signal length can be arbitrarily set as required, but it is particularly preferable to make the signal length longer than the spot diameter of the reproducing laser beam in order to accurately determine the multilevel signal level.
[0132]
The “multilevel signal level” referred to here is a signal level defined by the magnetization state of each magnetic domain, for example, the states “0”, “1”, “2” in FIG. 82 or FIG. The signal level defined by the relative signal output and the total magnetization state of the magnetic domain pattern in which a plurality of minute magnetic domains are continuous, for example, the states ("0", "2"), ("1") in FIG. , “2”) and (“0”, “1”). In the example of FIG. 82 or 83, the “signal length” refers to the length of the magnetic domain that exhibits the magnetization states of “0”, “1”, and “2”. In the example of 83, the magnetic domain pattern showing the magnetization states of (“0”, “2”), (“1”, “2”), (“0”, “1”) is continuous. Refers to the length. By making this longer than the spot diameter of the reproducing laser beam, the signal level before and after the signal level at each level of the test signal for setting the slice level of each signal is a region that does not cause a level shift due to optical interference. can do. In consideration of a magnetic super-resolution magneto-optical recording medium, it is more preferable that each level of the test signal has a region that does not cause a level shift due to optical interference with the preceding and following signal levels.
[0133]
When reproducing the multi-level recording signal, as shown in FIG. 50, when the test signal is reproduced, the levels 1 to n of the multi-level signal level are sampled and held, and the sample hold levels V of the signal levels k and k + 1 are obtained._k And V_{k + 1} Slice level (V) for discriminating signal levels k and k + 1 from_k + V_{k + 1} ) / 2.
[0134]
The test signal can be recorded at the beginning of the data recording unit, or can be provided at regular intervals in the data recording unit. The data recording unit may be the entire sector in the case of a medium having a sector structure, or may be an area included in a signal for synchronizing clocks. Further, it may be a data modulation / demodulation block, or may be inserted at an arbitrary number of bytes.
[0135]
<Eighth example of multi-value recording method>
The multilevel recording method of this example is characterized in that a test signal for accurately determining the timing for detecting the edge of a multilevel recording signal is recorded on a magneto-optical recording medium. Similarly, a magneto-optical recording medium having the format shown in FIGS. 20 and 21 is used.
[0136]
That is, the magneto-optical recording medium is driven in the same manner as in the first example of the multi-value recording method, the optical head is positioned at a track having a desired address, and the magnetic head is positioned near the desired track. While applying an external magnetic field according to recording data, a laser beam is irradiated from the optical head to record a multi-value signal corresponding to the external magnetic field. At this time, a test signal for generating a reference signal for timing for reproducing the edge of the recorded multilevel signal is recorded in the test area 17 of FIG. 21, and the signal is reproduced to generate the reference timing for edge detection. Can be done.
[0137]
As shown in FIG. 51, the data pattern of the test signal has at least one edge between all the multilevel signal levels. The signal length can be arbitrarily set as required. However, in order to prevent optical phase shift of each multilevel level, the signal length may be longer than ½ of the spot diameter of the reproduction laser beam. Particularly preferred. In addition, when considering a magneto-optical recording medium of a magnetic super-resolution type, an edge interval longer than a length that does not cause a level shift due to optical interference with the signals of the front and rear edges of the signal of each edge of the test signal. It is more preferable to set.
[0138]
Also in this example, the “multilevel signal level” is a signal level defined by the magnetization state of each magnetic domain, for example, the states “0”, “1”, “2” in FIG. 82 or FIG. 82 and FIG. 83, for example, the states (“0”, “2”), (“1” in FIG. 82 or 83. "," 2 ") and (" 0 "," 1 "). In the example of FIG. 82 or 83, the “signal length” refers to the length of the magnetic domain that exhibits the magnetization states of “0”, “1”, and “2”. In the example of 83, the magnetic domain pattern showing the magnetization states of (“0”, “2”), (“1”, “2”), (“0”, “1”) is continuous. Refers to the length. By making this longer than ½ of the spot diameter of the reproducing laser beam, the signal at each edge of the test signal for generating a timing signal that serves as a timing reference for detecting the edge of the multilevel recording signal is: Edge shift due to optical interference with the signal level of the front and rear edges does not occur.
[0139]
When reproducing a multilevel recording signal, each edge is detected independently at the time of reproducing a test signal, and a reference timing for the edge detection signal is generated. At the time of data signal reproduction, each edge is detected independently, and each edge detection signal is synthesized based on the edge detection timing of the test signal as shown in FIG.
[0140]
Also in this example, the test signal can be recorded at the beginning of the data recording unit, or can be provided at regular intervals in the data recording unit. The data recording unit may be the entire sector in the case of a medium having a sector structure, or may be an area included in a signal for synchronizing clocks. Further, it may be a data modulation / demodulation block, or may be inserted at an arbitrary number of bytes.
[0141]
<Ninth example of multi-value recording method>
In the multi-level recording method of this example, in order to accurately determine the multi-level signal level, a test signal for setting a slice level for discriminating the signal is recorded on the magneto-optical recording medium, and the edge of the multi-level recording signal A test signal for accurately determining the timing of detecting the recording is recorded on the magneto-optical recording medium. A magneto-optical recording medium having the format shown in FIGS. 20 and 21 is used.
[0142]
That is, the magneto-optical recording medium is driven in the same manner as in the first example of the multi-value recording method, the optical head is positioned at a track having a desired address, and the magnetic head is positioned in the vicinity of the desired track. While applying an external magnetic field according to recording data from the head, a laser beam is irradiated from the optical head to record a multilevel signal according to the external magnetic field. At this time, a test signal for setting a slice level for discriminating the recorded multilevel signal and a test signal for generating a reference signal for reproducing the edge of the recorded multilevel signal are displayed in the test area 17 of FIG. By recording and reproducing the signal, the slice level can be set and the reference timing for edge detection can be generated.
[0143]
The data pattern of each test signal and the reproduction method of the multi-value recording signal are the same as those in the seventh and eighth examples of the above-described multi-value recording method, and thus description thereof is omitted to avoid duplication.
[0144]
Also in this example, the test signal can be recorded at the beginning of the data recording unit, or can be provided at regular intervals in the data recording unit. The data recording unit may be the entire sector in the case of a medium having a sector structure, or may be an area included in a signal for synchronizing clocks. Further, it may be a data modulation / demodulation block, or may be inserted at an arbitrary number of bytes.
[0145]
<Tenth example of multi-value recording method>
As a means for performing mark edge recording on a magneto-optical recording medium, as shown in FIG. 53, recording magnetic domains are formed at a constant period, and the edge position of the recording magnetic domain is sufficiently smaller than the recording magnetic domain period in accordance with an information signal. The range was modulated stepwise over two steps. By combining this method with the magneto-optical recording medium for multi-level recording of the present invention, two-dimensional multi-level recording in the time direction (track direction) and the amplitude direction can be realized. The recording magnetic domain formation cycle is more preferably a magnetic domain length and a magnetic domain interval that are longer than the length that does not cause an edge shift due to optical interference between a signal of an arbitrary edge and a signal of an edge before and after that.
[0146]
As a recording method, the recording laser beam and the external magnetic field are simultaneously modulated and recorded, and the recording laser beam irradiation intensity, irradiation time, irradiation timing, external magnetic field intensity applied thereto, switching timing, etc. A method of modulating in accordance with recorded information is used.
[0147]
FIG. 54 shows an example in which the irradiation pulse width of the recording laser beam is modulated stepwise in accordance with the recording information signal. In magneto-magnetic modulation recording, the range where the magneto-optical recording medium is heated to a recordable temperature becomes a magnetic domain corresponding to the external magnetic field when the medium is cooled, so the edge position is at the irradiation start timing of the recording laser beam. It depends heavily. Therefore, as shown in FIG. 55, it is also possible to modulate the irradiation timing stepwise according to the recording information signal with a constant pulse width. Further, in order to prevent edge shift due to the remaining thermal history, as shown in FIG. 56, the front edge of the light irradiation pulse corresponds to the recording information signal and the rear edge corresponds to the next recording information signal. May be modulated step by step.
[0148]
FIG. 57 shows an example in which the irradiation intensity of the recording laser beam is modulated stepwise in accordance with the recording information signal. When the irradiation intensity of the recording laser beam is modulated, the size of the recording magnetic domain, that is, the magnetization state and length of the recording magnetic domain is modulated in accordance with the light intensity. Can be controlled. Moreover, it is not limited to the light intensity alone, but can be used in combination with light irradiation timing control and light irradiation pulse width control.
[0149]
FIG. 58 shows an example in which the edge position is controlled by modulating the intensity of the external magnetic field. When the intensity of the external magnetic field applied to the magneto-optical recording medium is changed, the size of the recording magnetic domain is changed, so that the edge position can be controlled as in the case of modulating the irradiation intensity of the recording laser beam. Of course, this can be used in combination with light intensity control, light irradiation timing control, and light irradiation pulse width control.
[0150]
FIG. 59 shows an example in which the edge position is controlled by modulating the application timing of the external magnetic field. In this case, since the edge position of the recording magnetic domain corresponds to the switching position of the applied magnetic field, the recording laser beam may be not only a pulse but also DC light.
[0151]
<Eleventh example of multi-value recording method>
In light-magnetic field modulation recording, the basic magnetic domain shape is determined by the light intensity and the light pulse width. As shown in FIG. 60, by simultaneously controlling the intensity of the recording laser beam and the recording pulse width, the recording magnetic domain width can be changed while keeping the recording magnetic domain length constant. That is, since each recording level can be changed minutely by this, multilevel recording can be realized by performing minute modulation of the level corresponding to the information signal. When decoding with the two-dimensional multi-value recording shown in the ninth example of the multi-value recording method, the three parameters of the edge position of the recording magnetic domain, the level position corresponding to the magnetization state, and the level position corresponding to the width of the magnetic domain 3D multi-value recording can be realized.
[0152]
<Twelfth example of multi-value recording method>
The multi-value recording method of this example is characterized by using a sample servo system as a tracking control system of the optical head. As the magneto-optical recording medium, one having the format shown in FIG. 21 and FIG. 61 (a) is used.
[0153]
As shown in FIGS. 21 and 61A, in the magneto-optical recording medium of this example, the recording track 11 is divided into a number of data recording units (segments) 12, and each data recording unit (segment) 12 is Are provided with a servo area 14 and a data recording area 15. The servo area 14 is provided with tracking pits 16 and embedded pits 18 in advance.
[0154]
FIG. 62 is a block diagram of a recording / reproducing apparatus suitable for such a sample servo type magneto-optical recording medium. The laser beam emitted from the laser forms a spot on the recording layer by a focusing lens. On the other hand, a magnetic coil (magnetic head) is disposed in the vicinity of the laser spot so that a magnetic field intensity-modulated with a multilevel signal can be applied to the recording layer. A laser beam emitted from the laser is irradiated along the recording track 11, and tracking of the laser beam is performed by detecting a tracking pit 16 provided in the servo region 14. On the other hand, in recording and reproduction of signals, a channel clock is generated by a PLL circuit from a signal detected from the embedded pit 18 provided in the servo area 14, and a laser driving circuit, a multi-level encoder, and a multi-level decoding are generated by this channel clock. By controlling the vessel.
[0155]
In a magneto-optical disk, generally, the DC level of a reproduction signal varies due to a minute variation in birefringence of a substrate. On the other hand, the sample servo type magneto-optical disk has 1000 or more segments per track, and the DC level of the reproduction signal can be considered to be constant within the range. Therefore, by providing an unrecorded area in which no signal is recorded in a part of each segment, for example, the test area 17, the DC level fluctuation can be corrected based on the reflectance of the unrecorded area. Identification of the value recording signal can be facilitated. FIG. 63 shows an example of a DC level correction circuit applied to the recording / reproducing apparatus of FIG. The level clamp gate controls the sample servo circuit (S / H circuit) to be held when a reproduction signal from the unrecorded area is detected.
[0156]
<Thirteenth example of multi-value recording method>
The multi-level recording method of this example uses the multi-level recording signal amplitude (multi-level recording magnetic domain width) regardless of the temperature of the driving device, the environmental temperature, the variation in the performance of the driving device, the variation in the characteristics of the magneto-optical recording medium, etc. A test signal for constant control is recorded in a test area provided outside the user area of the magneto-optical recording medium, the reproduction signal is compared with a reference signal, and the recording laser power and / or the recording laser pulse width are determined. It is characterized by controlling. A magneto-optical recording medium having the format shown in FIGS. 22 and 23 is used.
[0157]
First, the magneto-optical recording medium is mounted on the recording / reproducing apparatus, and the optical head is positioned at a desired address in the test area 22. Further, the magnetic head is positioned in the vicinity of the desired track. Thereafter, the optical head and the magnetic head are driven, and a fixed test pattern in which multi-value recording signals to be recorded on the magneto-optical recording medium are combined is recorded in the test area. Next, the test signal is reproduced, the signal amplitude is compared with the reference signal amplitude, and the recording temperature on the magneto-optical recording medium is controlled to be constant.
[0158]
The recording of the test signal can be performed at an appropriate timing if necessary after the magneto-optical recording medium is mounted on the recording / reproducing apparatus. For example, it can be performed when the magneto-optical recording medium is mounted on the recording / reproducing apparatus, or can be performed when the operation of the recording / reproducing apparatus is started. It can also be performed immediately before the signal recording operation on the magneto-optical recording medium. Furthermore, the recording can be performed at regular time intervals after the magneto-optical recording medium is mounted on the recording / reproducing apparatus.
[0159]
As shown in FIG. 64 (a), the test pattern is recorded in such a manner that a constant level external magnetic field is applied in a pulsed manner so that a reproduction signal approximated between two adjacent signal levels of a multilevel recording signal can be obtained. However, the laser power is changed continuously or stepwise and performed at a single frequency. In this example, for each multi-level recording level, the test pattern was recorded by switching the laser power in 8 steps by 0.1 mW. FIG. 64B shows the reproduced signal waveform. Then, the minimum and maximum values of the signal are peak-held for each reproduction signal of the recording power, the signal amplitude is obtained, the difference between the signal amplitude and the reference signal amplitude is the smallest, and the difference is The condition that is below a certain value is the optimum recording condition. If the optimum recording condition is not found, test recording is repeated with the laser power increased. If the optimum recording condition is not found even when the maximum power of the recording / reproducing apparatus is exceeded, the operation ends as an error.
[0160]
FIG. 65 shows a block diagram of the optimum condition detection circuit. The reference signal amplitude can be obtained from a signal recorded in advance outside the user area on the medium and outside the test area. It is also possible to read data relating to the reference signal amplitude recorded in advance on the medium and generate it by the recording / reproducing apparatus. Furthermore, data relating to the reference signal amplitude can be stored in advance in a memory provided in the recording / reproducing apparatus.
[0161]
In the previous example, the test pattern was recorded by changing the laser power. However, the test pattern can be recorded by changing the recording pulse width, and further, the test can be performed by changing both the laser power and the recording pulse width. A pattern can also be recorded.
[0162]
<14th example of multi-value recording method>
The multi-level recording method of this example uses the multi-level recording signal amplitude (multi-level recording magnetic domain width) regardless of the temperature of the driving device, the environmental temperature, the variation in the performance of the driving device, the variation in the characteristics of the magneto-optical recording medium, etc. A test signal for constant control is recorded in a test area provided outside the user area of the magneto-optical recording medium, and the recording external magnetic field is controlled from the reproduced signal so that the amplitude between each multilevel recording level becomes equal. It is characterized by doing. A magneto-optical recording medium having the format shown in FIGS. 22 and 23 is used.
[0163]
As in the thirteenth example, first, the magneto-optical recording medium is mounted on the recording / reproducing apparatus, and the optical head is positioned at a desired address in the test area 22. Further, the magnetic head is positioned in the vicinity of the desired track. After that, the optical head and the magnetic head are driven to record a fixed test pattern in which the multi-value recording signal to be recorded on the magneto-optical recording medium is recorded in the test area. The external magnetic field is controlled so that the signal amplitude becomes constant.
[0164]
As shown in FIG. 66 (a), test pattern recording includes all of the multi-value recording levels, and changes the external magnetic field of each other multi-value recording level with reference to two of the multi-value recording levels. The test pattern to be used is used. In this example, the test pattern was recorded by switching the external magnetic field to four levels for each multilevel recording signal level. FIG. 66 (b) shows the reproduced signal waveform. Then, the signal level is sampled and held for each reproduction signal of the recording magnetic field to obtain the signal amplitude. Further, the obtained multi-level signal levels are compared, and a combination of external magnetic fields in which the signal level intervals are equal is set as the optimum recording condition. FIG. 67 shows a block diagram of an optimum condition detection circuit suitable for the recording / reproducing method of this example.
[0165]
Others are the same as the recording / reproducing method of the thirteenth example, and thus the description is omitted to avoid duplication.
[0166]
<Fifteenth example of multi-value recording method>
The multilevel recording method of this example is a recording signal of a multilevel recording signal in a magneto-optical recording / reproducing apparatus that performs magneto-optical modulation recording, regardless of the temperature of the driving apparatus, the environmental temperature, the driving apparatus variation, or the magneto-optical recording medium variation. In order to control the amplitude (multi-value recording domain width) to be constant, at least one of the laser beam power and the laser beam pulse width is changed, and a test signal is recorded at two or more optical pulse periods. It is characterized in that at least one of the recording laser power and the laser light pulse width is controlled so that the difference between the average values of the levels becomes a constant value. As an example of the magneto-optical recording medium, one having the format shown in FIGS. 22 and 23 is used.
[0167]
As in the thirteenth and fourteenth examples of the multi-value recording method, first, the magneto-optical recording medium is mounted on the recording / reproducing apparatus, and the optical head is positioned at a desired address in the test area 22 *. Further, the magnetic head is positioned in the vicinity of the desired track. Thereafter, the optical head and the magnetic head are driven, and the multi-level recording signal to be recorded on the magneto-optical recording medium is recorded in the test area with two or more optical pulse periods, the laser light power and the laser light pulse width. Record at least one of the changes. Next, the test signal is reproduced, and the difference between the average values of the signal levels of the reproduction signals having the two or more periods is made constant, thereby controlling the recording magnetic domain width of the magneto-optical recording medium to be constant. .
[0168]
As shown in FIG. 68 or 69, the test recording is performed with two or more types of recording laser light pulse periods between two levels having the largest amplitude of the multilevel recording signal. At least one of the two recording laser light pulse periods is set to a period where the recording magnetic domains of the period do not overlap, and at least one period is set to a period where the recording magnetic domains of the period overlap. Recording is performed by stepwise changing the recording laser power while applying a recording external magnetic field having a constant intensity while switching the polarity at the timing as shown in FIG. FIG. 70 shows the reproduction signal waveform of FIG. FIG. 71 shows the reproduction signal waveform of FIG. In both the case of FIG. 70 and FIG. 71, when the recording laser power is changed, the signal recorded with a period in which the recording magnetic domains do not overlap with respect to the average value of the signal level of the signal recorded with the period in which the recording magnetic domains overlap. The average value of the signal level changes greatly. For all the recording conditions changed stepwise, the difference (Δ1) between the average values of the two periods is detected, and the condition where the value of Δ1 is closest to the reference value is set as the optimum recording condition. At this time, if the preset reference value is 0, it is difficult to be affected by variations in magneto-optical recording medium, DC offset and drift of the circuit, and therefore, the period in which the recording magnetic domains do not overlap so that the reference value becomes 0 is effective. It is desirable to make the diameter of the light spot approximately equal.
[0169]
FIG. 72 shows an example of a block diagram of the optimum condition detection circuit. The reproduced test signal passes through a low-pass filter having a cut-off frequency sufficiently lower than the recording laser pulse period, and becomes an average value of the reproduction signal level of each recording laser pulse period. Then, Δ1 can be detected by peak-holding the maximum value and the minimum value of the signal and taking the difference.
[0170]
Others are the same as the recording / reproducing method of the thirteenth example, and thus the description is omitted to avoid duplication.
[0171]
<Sixteenth example of multi-value recording method>
The multi-value recording method of this example is characterized in that a multi-value recording signal is recorded on a multi-value recording magneto-optical recording medium rather than the number of magnetic field regions in a stable recording state of the magneto-optical recording medium. To do. As the magneto-optical recording medium, the magneto-optical recording medium according to the first configuration example and the second configuration example described above can be used. Here, the magneto-optical recording medium for quaternary recording (according to the first configuration example) is used. A case of recording 16 values using a magneto-optical recording medium (specifically, a magneto-optical recording medium of FIGS. 9 to 13) will be described.
[0172]
First, a magneto-optical recording medium is mounted on a medium driving unit such as a turntable, an optical head is disposed on the transparent substrate side, and a magnetic head is disposed on the protective layer side. The medium drive unit is activated to relatively drive the magneto-optical recording medium, the optical head, and the magnetic head at a predetermined linear velocity, and position the optical head and the magnetic head on a predetermined track. Thereafter, a signal beam is recorded by applying a magnetic field pulse-modulated with a desired recording signal from the magnetic head while irradiating a laser beam with a constant intensity along the predetermined recording track from the optical head. .
[0173]
In this case, as shown in FIG. 73, the quaternary recording signal (00312200120321331130230113203210) is divided by two from the head, thereby (00) (31) (22) (00) (12) (03) (21) (33 ) (11) (30) (23) (01) (13) (20) (32) (10), and the first signal and the second signal of each set are further converted. By taking out separately, it divides | segments into the 1st signal sequence of (03201023133201231) and the 2nd signal sequence of (0120231310313020).
[0174]
When the laser beam reaches the start position of the desired recording track, the intensity of the laser beam irradiated from the optical head is set to the recording level P.₁ And a magnetic field H that is pulse-modulated by the first signal train from the magnetic head.₁ Is applied. As a result, as shown in FIG. 73A, a wide first write signal string 201 is formed on the magneto-optical recording medium.
[0175]
Next, the laser beam is positioned again at the head position of the recording track on which the first write signal string 201 is formed, and the first write signal string 201 can be rewritten with the intensity of the laser beam irradiated from the optical head. Level P₂ (P₁> P₂), And the magnetic field H that is pulse-modulated by the second signal train from the magnetic head.₂ Is applied. As a result, as shown in FIG. 73A, a second write signal string 202 narrower than the width of the first write signal string 201 is formed at the center of the first write signal string 201. Note that the width of the second write signal string 202 is made smaller than the width of the first write signal string 201 and a part of the first write signal string 201 is rewritten to the second write signal string 202. It is also possible to change the spot size by using a plurality of laser beams having different values.
[0176]
The recording signal can be reproduced by irradiating a reproducing laser beam 210 having a spot diameter D larger than the width of the first write signal string 201 along the recording track. That is, when the reproducing laser beam 210 having a spot diameter D larger than the width of the first write signal string 201 is irradiated along the recording track, as shown in FIG. 73 (b), the first and second signal strings. And the signal of the first signal train is “3”, the signal of the first signal train is “3”, the signal of the second signal train is “2”, and the signal of the first signal train is “3”. The region where the signal of the second signal sequence is “1”, the region where the signal of the first signal sequence is “3” and the signal of the second signal sequence is “0”, and the signal of the first signal sequence The region where the signal of the second signal sequence is “3” with “2”, the region where the signal of the first signal sequence is “2” and the signal of the second signal sequence is “2”, and the first signal An area where the signal of the column is “2” and the signal of the second signal string is “1”, an area where the signal of the first signal string is “2” and the signal of the second signal string is “0”; The signal in the first signal sequence is An area where the signal of the second signal train is “3” at 1 ”, an area where the signal of the first signal train is“ 1 ”and the signal of the second signal train is“ 2 ”, and the first signal train The signal of “1” and the signal of the second signal train is “1”, the signal of the first signal train is “1” and the signal of the second signal train is “0”, An area where the signal of the first signal train is “0” and the signal of the second signal train is “3”, and the signal of the first signal train is “0” and the signal of the second signal train is “2”. In the region, the region where the signal of the first signal sequence is “0” and the signal of the second signal sequence is “1”, and the region where both the signals of the first and second signal sequences are “0”, Since the total magnetization state of the region irradiated with the reproduction laser spot 210 is different, a 16-value recording signal can be detected by assigning “0” to “15” to the total magnetization state in each region. .
[0177]
As described above, according to the recording / reproducing system of this example, 16-value recording of a signal can be realized by using a quaternary recording medium, so that a magneto-optical recording medium having a large amount of recorded information can be provided at a low cost.
[0178]
Of course, the same 16-value recording can be executed by the light modulation method instead of the magnetic field modulation method.
[0179]
<Seventeenth example of multi-value recording method>
The multi-value recording method of this example is characterized in that 16-value signals are recorded on a magneto-optical recording medium for quaternary recording by an optical-magnetic field modulation method.
[0180]
As in the case of the sixteenth example, a magneto-optical recording medium is mounted on a medium driving unit such as a turntable, an optical head is disposed on the transparent substrate side, and a magnetic head is disposed on the protective layer side. The medium drive unit is activated to relatively drive the magneto-optical recording medium, the optical head, and the magnetic head at a predetermined linear velocity, and position the optical head and the magnetic head on a predetermined track. Thereafter, as shown in FIG. 74, the optical head irradiates a laser beam whose intensity is modulated in a pulse shape along the predetermined recording track, and the magnetic head performs a pulse modulation on the desired recording signal. A signal is recorded by applying a magnetic field.
[0181]
The recording signal is divided into a first signal string and a second signal string in the same manner as in the sixteenth example. When the laser beam reaches the start position of the desired recording track, the laser beam irradiated from the optical head is switched to a pulse shape and the intensity is changed to the recording level P.₁ Switch to. Further, the magnetic field H modulated in a pulse shape by the first signal train from the magnetic head.₁ Is applied. As a result, as shown in FIG. 74A, a wide first write signal string 201 is formed on the magneto-optical recording medium. The pulsed recording laser beam is irradiated at the timing when the external magnetic field applied from the magnetic head reaches the target value.
[0182]
Next, the laser beam is positioned again at the head position of the recording track on which the first write signal string 201 is formed, and the laser beam irradiated from the optical head is switched to a pulse shape, and its intensity is changed to the first write signal. Level P at which signal train 201 can be rewritten₂ (P₁> P₂). Further, the magnetic field H modulated in a pulse shape by the second signal train from the magnetic head.₂ Is applied. As a result, as shown in FIG. 74A, a second write signal string 202 narrower than the width of the first write signal string 201 is formed at the center of the first write signal string 201. Also in this case, the pulsed recording laser beam is irradiated at the timing when the external magnetic field applied from the magnetic head reaches the target value. In the recording / reproducing method of this example, the emission timing of the recording laser beam is shifted by time t between the first recording and the second recording. In this way, as shown in FIG. 75, the waveform of the reproduction signal detected from each region becomes sharper than when the emission timings of the first and second recording laser beams are aligned. . The time t is adjusted to a value at which the waveform of the reproduction signal becomes the sharpest.
[0183]
As in the case of the sixteenth example, the recording signal can be reproduced by irradiating the reproducing laser beam 210 having a spot diameter D larger than the width of the first write signal train 201 along the recording track. That is, when the reproducing laser beam 210 having a spot diameter D larger than the width of the first write signal string 201 is irradiated along the recording track, as shown in FIG. And the signal of the first signal train is “3”, the signal of the first signal train is “3”, the signal of the second signal train is “2”, and the signal of the first signal train is “3”. The region where the signal of the second signal sequence is “1”, the region where the signal of the first signal sequence is “3” and the signal of the second signal sequence is “0”, and the signal of the first signal sequence The region where the signal of the second signal sequence is “3” with “2”, the region where the signal of the first signal sequence is “2” and the signal of the second signal sequence is “2”, and the first signal An area where the signal of the column is “2” and the signal of the second signal string is “1”, an area where the signal of the first signal string is “2” and the signal of the second signal string is “0”; The signal in the first signal sequence is An area where the signal of the second signal train is “3” at 1 ”, an area where the signal of the first signal train is“ 1 ”and the signal of the second signal train is“ 2 ”, and the first signal train The signal of “1” and the signal of the second signal train is “1”, the signal of the first signal train is “1” and the signal of the second signal train is “0”, An area where the signal of the first signal train is “0” and the signal of the second signal train is “3”, and the signal of the first signal train is “0” and the signal of the second signal train is “2”. In the region, the region where the signal of the first signal sequence is “0” and the signal of the second signal sequence is “1”, and the region where both the signals of the first and second signal sequences are “0”, Since the total magnetization state of the region irradiated with the reproduction laser spot 210 is different, a 16-value recording signal can be detected by assigning “0” to “15” to the total magnetization state in each region. .
[0184]
According to the present embodiment, in addition to the same effect as the 16th embodiment, the pulsed recording laser beam is irradiated at the timing when the external magnetic field applied by the magnetic head reaches the target value. The edges of each magnetization domain become sharp and the margin for jitter can be increased. In addition, since the emission timing of the recording laser beam is shifted between the first recording time and the second recording time, the emission timing of the first recording laser beam and the second recording laser beam are aligned. A sharper reproduction signal can be obtained from each region. Therefore, pit edge recording becomes possible due to these effects.
[0185]
If the recording signal is divided into three signal strings and these three signal strings are overwritten on the same track, 64-value signal recording can be performed based on the same principle.
[0186]
<Eighteenth example of multi-value recording method>
The multi-value recording method of this example is characterized in that a signal is recorded and reproduced with respect to a magneto-optical recording medium in which minute pre-pits are formed at minute intervals along a recording track. The following can be considered as the configuration and usage of this magneto-optical recording medium.
[0187]
a. A magneto-optical recording layer is formed on a substrate having a pre-pit group divided into data units in an information recording area, and a magneto-optical signal is recorded in or between the pre-pits.
[0188]
b. A. A recording film capable of multi-value recording is laminated on the medium.
[0189]
c. A. The pre-pit groups are regularly arranged for each track. They are arranged on a straight line in the radial direction or shifted by a half cycle. This enables quantization of crosstalk.
[0190]
d. A. In this medium, the film composition and film thickness can be changed inside and outside the prepits.
[0191]
e. A. A pre-pit of the medium is formed smaller than the reproducing light spot diameter, and a recording film capable of magnetic super-resolution is laminated thereon.
[0192]
f. In addition, said a. ~ E. The above-described various multilevel recording methods are applied to the medium.
[0193]
In the magneto-optical recording medium, improvement of the recording density is one of the most important technical problems. The recording density can be improved by making the recording magnetic domain smaller and recording the signal in the track direction. However, if the recording magnetic domain is miniaturized, signals reproduced from adjacent magnetic domains are likely to interfere with each other and cannot be separated.
[0194]
When minute prepits are formed along a recording track at minute intervals, when a reproducing laser beam is irradiated along the recording track, a portion where there is no reflected light signal and no prepits due to light diffraction or interference. Therefore, the presence or absence of pre-pits can be detected by detecting the reflected light signal (so-called sum signal). On the other hand, the magneto-optical signal (so-called difference signal) recorded on the magnetic film can be detected by detecting the magnetization direction of the recording magnetic domain regardless of the presence or absence of the prepit. Therefore, if the recording magnetic domain is formed in a positional relationship with the pre-pits, the position of the recording magnetic domain can be clarified even if the recording magnetic domain is miniaturized, the signal can be easily separated, and the recording density can be improved. .
[0195]
FIG. 76 shows a case where the recording magnetic domain 302 is formed on the prepit 301. In this example, since the sum signal and the difference signal have a one-to-one correspondence, the recording magnetic domain 302 can be detected by detecting the peak of the sum signal.
[0196]
77A shows a case where the recording magnetic domain 302 is formed so that the leading edge of the recording magnetic domain 302 overlaps the prepit 301, and FIG. 77B shows a plurality (in this example) between adjacent prepits 301. The case where three (3) recording magnetic domains 302 are formed is shown. FIG. 77C shows a case where the arrangement center of the prepit 301 is shifted from the arrangement center of the recording magnetic domain 302, and FIG. 77D shows that the arrangement center of the prepit 301 is shifted from the arrangement center of the recording magnetic domain 302. The case where a plurality (three in this example) of recording magnetic domains 302 are formed between adjacent prepits 301 is shown.
[0197]
FIG. 78 (a) shows a case where the prepit 301 is formed in a convex shape, and FIG. 78 (b) shows a case where the prepit 301 is formed in an elliptical shape. FIG. 78 (c) shows a case where one recording magnetic domain 302 is formed on two convex prepits 301a, 301b, and FIG. 78 (d) shows a case where two concave prepits 301a, 301b are formed. A case where one recording magnetic domain 302 is formed is shown.
[0198]
FIG. 79 shows a case where the pre-pits 301 are formed with regularity not only in the track direction but also in the inter-track direction. As described above, when the positional relationship between the prepits on the adjacent track is made regular and the recording magnetic domain is formed by using this as a guide, the leakage of the recording signal from the adjacent track, the so-called crosstalk level is quantized by the recording pattern. It can be made into a level.
[0199]
FIG. 80 shows a state where the reproduction laser spot 210 is scanned so that the center of the reproduction laser spot 210 passes through the center track. In this way, the reproduction signal level is output as a multilevel signal separated into six levels by combination with the recording patterns of the tracks on both sides. The original signal is reproduced by canceling the leaked signal due to the mutual relationship of the signals reproduced so that the center of the reproduction laser spot 210 passes through the center of each track. In this case, since it is reproduced once as multi-value recording and separated into six stages, it is easy to cancel crosstalk.
[0200]
In the recording / reproducing method of this example, a plurality of recording pits exist in the reproducing light spot in the laser traveling direction or cross-track direction, and each level of the reproduced signal expressed by each combination of the recording states is defined. This is a multi-stage recording / reproducing system, which is not limited to a multi-level magneto-optical recording medium but also a signal that uses a normal binary recording magneto-optical recording medium or a magnetic super-resolution type magneto-optical recording medium. It can also be applied to recording and playback.
[0201]
Hereinafter, other multi-value recording methods of the present invention will be listed.
[0202]
(1) The relative signal output intervals corresponding to the respective recording states are made equal by adjusting the refractive index and film thickness of each film laminated on the transparent substrate and the Kerr rotation angle of the perpendicular magnetization film. For example, in the case of a ternary recording medium, as shown in FIG. 81, the level intervals of the recording signals corresponding to the states “0”, “1”, and “2” are made equal. In this way, the S / N of the reproduction signal with respect to the transition of each level interval of the recording signal becomes uniform, and the signal efficiency is improved overall. This method is particularly effective when the size of the minimum recording magnetic domain is relatively large with respect to the spot diameter of the reproducing light, for example, when it is equal to or larger than ½ of the spot diameter.
[0203]
(2) Signal level generated by inter-waveform interference of minute magnetic domains when the size of the minimum recording magnetic domain is smaller than the spot diameter of the reproducing light, particularly when recording with a size of 1/2 or less of the spot diameter. And a signal level generated from a large magnetic domain in each recording state.
[0204]
When the size of the minimum recording magnetic domain is relatively small with respect to the spot diameter of the reproduction light, for example, when it is ½ or less of the spot diameter, if this continues, the signal output is caused by the inter-waveform interference of the reproduction signal. Take the intermediate value of both states. For example, in the case where minute recording magnetic domains having the same size of the state “0” and the state “2” are repeatedly recorded on the multilevel recording medium of the present invention, as shown in FIG. It becomes the same level as the reproduction signal of the magnetic domain relatively large with respect to the diameter, and the two cannot be distinguished.
[0205]
Therefore, if the signal level generated by inter-waveform interference of minute magnetic domains is different from the signal level generated from a large magnetic domain in each recording state, state “0”, state “1”, state “2”, and state “ Inter-waveform interference level between “0” and state “1”, inter-waveform interference level between state “0” and state “2”, inter-waveform interference between state “1” and state “2” By assigning a signal to each level, higher-order multilevel recording becomes possible.
[0206]
The signal levels do not coincide with each other and are preferably equally spaced. The method includes a method using a medium and a method using a recording method. As a method performed on the medium, as shown in FIG. 83, each film is positioned so that a signal level generated from a large magnetic domain in each recording state is positioned at a signal level different from a signal level generated by inter-waveform interference of micro magnetic domains. There are methods for setting multiple interference conditions. Further, as a method performed by the recording method, as shown in FIG. 84, the signal level generated by the inter-waveform interference of the minute magnetic domains is located at a position different from the signal level generated from the large magnetic domain in each recording state. There is a method of controlling the area ratio of the recording magnetic domain. Specifically, when the medium is inserted into the recording / reproducing apparatus, the apparatus tries to record by changing the area ratio of the minute recording magnetic domains, and the signal levels generated from the large magnetic domains in each recording state are mutually matched. However, it is possible to adopt a method of selecting an area ratio that is preferably set at equal intervals. Further, the method performed with these media and the method performed with the recording method can be used in combination. According to this combined method, the signal levels can be adjusted more easily, and the signal level intervals can be made equal. Further, the signal level can be adjusted to an arbitrary position by controlling the area ratio of the recording magnetic domain.
[0207]
(3) A mark edge recording method for a multi-value recording medium and a signal reproduction method from a medium on which mark edge recording has been performed by the method.
FIG. 85 shows a mark edge recording method in which ternary information is carried at the end (mark edge) of a recording magnetic domain, and a signal reproduction method from a multi-value recording medium on which mark edge recording has been performed by this method. As the magneto-optical recording medium, a magneto-optical recording medium capable of recording ternary information on the magnetic layer is used.
[0208]
First, a mark edge recording method for the magneto-optical recording medium will be described. In order to record ternary information “0”, “1”, “2” on the magneto-optical recording medium, the magnetization state of the magnetic layer (in the case where there are a plurality of magnetic layers, the magnetization state of each magnetic layer) (Total magnetization state) must be switched to three stages. The three stages of magnetization states are A, B, and C (however, the magnitude of magnetization increases in the order of A <B <C), and as shown in FIG. "0" information is assigned to the part where the magnetization state A of the magnetic field is continuous, the part where the oblique magnetization state B switches to the white magnetization state A, and the part where the lattice magnetization state C switches to the white magnetization state A, Information of “1” is assigned to a portion where the white magnetization state A switches to the oblique magnetization state B, a portion where the oblique magnetization state B continues, and a portion where the lattice magnetization state C switches to the oblique magnetization state B, and ▼ Information by assigning information “2” to a portion where the magnetization state A of the white background switches to the magnetization state C of the lattice, a portion where the magnetization state B of the oblique line switches to the magnetization state C of the lattice, and a portion where the magnetization state C of the lattice continues. For example, if you record Value information (10202201210) can be recorded in mark train shown in FIG. 85 (a).
[0209]
Next, a method for reproducing a signal from a medium on which ternary information is recorded by mark edge by the above method will be described. When reproduction light is irradiated along the mark row in FIG. 85A, the reproduction signal waveform in FIG. 85B is obtained corresponding to the magnitude of the magnetization of each recording magnetic domain. When the reproduction signal output detected from the A recording magnetic domain is α, the reproduction signal output detected from the B recording magnetic domain is β, and the reproduction signal output detected from the C recording magnetic domain is γ, α <s₂ <Β <s₁ <Two different slice levels s satisfying the condition γ₁ , S₂ 85, slice the reproduced signal waveform of FIG.₁ , S₂ And the crossing point of the reproduction signal output is detected. In the middle column of FIG. 85 (b), each slice level s is displayed.₁ , S₂ The presence / absence of the signal detected in is indicated by the symbol “◯” or “−”. The top row in this column is the slice level s₁ Shows the detection pattern of the signal detected at, and the lower row shows the slice level s₂ The detection pattern of the signal detected by is shown. In these descriptions, the symbol “◯” indicates a case where a cross point is detected, and the symbol “−” indicates a case where a cross point is not detected.
[0210]
As is apparent from this figure, in this example, the slice level s₁ Detection signal and slice level s₂ Is combined with the detection signal of the slice level s₁ When the detection signal of “−” is “slice level s”₂ (Hereinafter, this combination is expressed as “−, ○”. Similarly, the slice level s₁ The detection signal of “” is preceded by the slice level s.₂ The cross point of will be described later. ), “◯, −”, “○, ○”, and “−, −”.
[0211]
Therefore, as shown in FIG. 85 (d), the previous data of each signal detector is stored, and (1) the previous data is “◯, ○” and the detection signal is “−, In the case of “-”, when the previous data is “−, ○” and the detection signal is “O, −”, the previous data is “−, −” and the detection signal is “O, ○”. In this case, “2” of the reproduction data is assigned. (2) If the previous data is “O, O” and the detection signal is “O, −”, the previous data is “−, O”. When the detection signal is “−, −”, when the previous data is “−, −” and the detection signal is “−, ○”, the reproduction data “1” is assigned. ▼ When the previous data is “○, ○” and the detection signal is “○, ○”, when the previous data is “−, ○” and the detection signal is “−, ○”, one is added to it. Previous data is “−, − When the detection signal is “−, −”, the reproduction data “0” is assigned to reproduce the original ternary information (10202201210) as shown in the bottom column of FIG. 103 (b). Can do.
[0212]
In FIG. 85, the mark edge recording / reproducing method in the case of using a ternary recording magneto-optical recording medium has been described as an example. However, a binary recording magneto-optical recording medium or multi-value more than quaternary recording is used. Even when a magneto-optical recording medium for recording is used, mark edge recording / reproduction of information can be executed in the same manner as described above.
[0213]
In the example shown in FIG. 85, the white magnetization state A is continuous, the hatched magnetization state B is switched to the white magnetization state A, and the lattice magnetization state C is switched to the white magnetization state A. "1" is assigned to a portion where the magnetization state A of the white background is switched to the hatched magnetization state B, a portion where the hatched magnetization state B is continuous, and a portion where the magnetization state C of the lattice is switched to the hatched magnetization state B. The information “2” is assigned to the portion where the magnetization state A of the white background is switched to the magnetization state C of the lattice, the portion where the magnetization state B of the oblique line is switched to the magnetization state C of the lattice, and the portion where the magnetization state C of the lattice is continuous. The information is recorded by assigning the information, but what information is assigned to the change in any magnetization state can be appropriately changed as necessary regardless of the present embodiment.
[0214]
A configuration example of a magnetic head device that can be applied to multi-level recording on a magneto-optical recording medium is shown below.
[0215]
<First Configuration Example of Magnetic Head Device>
As shown in FIG. 86, the magnetic head device of this example is characterized in that two windings are wound around one magnetic circuit, and these windings can be driven independently. This magnetic head device is disposed on the protective film side of the magneto-optical recording medium.
[0216]
The magnetic head device of this example can be applied to the first example, the fourth example, and the fifth example of the multi-value recording method. That is, when performing these multi-value recording methods, the magnetic head drive circuit 1 and the magnetic head drive circuit 2 for applying current to the two windings are driven independently in synchronization with the recording clock, so that the magneto-optical recording is performed. Since a multivalued external magnetic field can be applied to the medium, at the same time, by irradiating a light pulse synchronized with a recording clock, a signal can be multivalued recorded on the irradiated portion of the light pulse.
[0217]
The magnetic head device of this example can be applied to the second and third examples of the multi-value recording method. That is, a resonance circuit is formed by one of the windings and the magnetic head drive circuit, and a constant frequency magnetic field synchronized with the recording clock is generated, and a constant current is applied to the other winding to generate a constant bias magnetic field. By generating the magnetic field, it is possible to apply a magnetic field having a constant period offset from zero to the magneto-optical recording medium.
[0218]
In the above configuration example, the case where the number of windings is two has been described as an example, but the same configuration can be made when the number of windings is three or more.
[0219]
<Second Configuration Example of Magnetic Head Device>
As shown in FIG. 87, the magnetic head device of this example is characterized in that two magnetic heads that can be driven independently from each other are arranged close to each other. This magnetic head device is also disposed on the protective film side of the magneto-optical recording medium.
[0220]
The magnetic head device of this example can be applied to the fourth and fifth examples of the multi-value recording method. That is, when executing these multilevel recording methods, the magnetic head 1 and the magnetic head 2 are independently driven in synchronization with the recording clock, so that a multilevel external magnetic field can be applied to the magneto-optical recording medium. At the same time, by irradiating a light pulse synchronized with the recording clock, a signal can be recorded in a multi-valued manner on the light pulse irradiation portion.
[0221]
The magnetic head device of this example can be applied to the second and third examples of the multi-value recording method. That is, one magnetic head and a magnetic head drive circuit constitute a resonance circuit to generate a constant frequency magnetic field synchronized with the recording clock and apply a constant current to the other magnetic head to generate a constant bias magnetic field. By generating the magnetic field, it is possible to apply a magnetic field having a constant period offset from zero to the magneto-optical recording medium.
[0222]
<Third Configuration Example of Magnetic Head Device>
In the magnetic head device of this example, as shown in FIG. 88, two magnetic heads are arranged close to each other, and a permanent magnet for applying a bias magnetic field is arranged close to these two magnetic heads. And The two magnetic heads are configured to be driven independently of each other. The magnetic head device of this example is also disposed on the protective film side of the magneto-optical recording medium.
[0223]
The magnetic head device of this example can be applied to the fourth and fifth examples of the multi-value recording method. That is, when executing these multilevel recording methods, the magnetic head 1 and the magnetic head 2 are independently driven in synchronization with the recording clock, so that a multilevel external magnetic field can be applied to the magneto-optical recording medium. it can. Further, a constant bias magnetic field can be applied to the magneto-optical recording medium by the permanent magnet. Therefore, by irradiating a light pulse synchronized with the recording clock simultaneously with the application of the magnetic field, the signal can be recorded in a multi-valued manner on the irradiated portion of the light pulse.
[0224]
The magnetic head device of this example can be applied to the second and third examples of the multi-value recording method. That is, the magnetic head and the magnetic head driving circuit constitute a resonance circuit, and a constant frequency magnetic field synchronized with the recording clock is generated, and a constant bias magnetic field is applied by a permanent magnet, so that the constant magnetic field is offset from zero. A periodic magnetic field can be applied to the magneto-optical recording medium.
[0225]
Since the magnetic head device of this example includes a permanent magnet for applying a bias magnetic field, it is not necessary to apply a direct current component to the magnetic head. Thus, power consumption can be reduced and the signal transmission rate can be increased.
[0226]
<Fourth Configuration Example of Magnetic Head Device>
In the magnetic head device of this example, as shown in FIG. 89, two magnetic heads are arranged close to each other on the protective film side of the magneto-optical recording medium, and a leakage magnetic field from the aperture lens actuator is used as a bias magnetic field. It is characterized by that. Others are the same as those of the magnetic head device according to the third configuration example, and thus the description thereof is omitted.
[0227]
<Fifth Configuration Example of Magnetic Head Device>
As shown in FIG. 90, the magnetic head device of this example is characterized in that one magnetic head and a permanent magnet for applying a bias magnetic field are arranged close to each other on the protective film side of the magneto-optical recording medium.
[0228]
<Sixth Configuration Example of Magnetic Head Device>
In the magnetic head device of this example, as shown in FIG. 91, one magnetic head is arranged on the protective film side of the magneto-optical recording medium, and a leakage magnetic field from the focusing lens actuator is used as a bias magnetic field. And
[0229]
<Seventh Configuration Example of Magnetic Head Device>
In the magnetic head device of this example, as shown in FIG. 92, two magnetic heads are arranged close to each other, and an electromagnetic coil for applying a bias magnetic field is arranged close to these two magnetic heads. And The magnetic head device of this example is also disposed on the protective film side of the magneto-optical recording medium.
[0230]
<Eighth Configuration Example of Magnetic Head Device>
In the magnetic head device of this example, as shown in FIG. 93, two magnetic heads are arranged close to each other on the protective film side of the magneto-optical recording medium, and an electromagnetic coil for applying a bias magnetic field is narrowed down to surround the lens actuator. It is characterized by having been arranged in. The magnetic head device of this example is also disposed on the protective film side of the magneto-optical recording medium.
[0231]
The above-described embodiment is merely an example of the present invention. In addition, various signals can be obtained by combining an arbitrary medium according to the present invention, an arbitrary recording / reproducing system, and a recording / reproducing apparatus. Recording can be performed. In particular, the magnetic head device is not limited to the description of the above configuration example, but the number of windings of the magnetic head, the number and arrangement of the magnetic head, and the number of permanent magnets and electromagnetic coils that are means for applying a bias magnetic field. The arrangement and the like can be changed as appropriate.
[0232]
In the above embodiment, for ease of explanation, the film structure of the magneto-optical recording medium, its format, the multi-value recording / reproducing method, and the magnetic head device will be described separately, and combinations thereof will be described. Only representative ones were selectively listed. Therefore, the gist of the present invention is not limited to the combinations listed in the above embodiments, but any combination of the magneto-optical recording medium, the multi-value recording / reproducing method and the magnetic head device described in the above embodiments, Multi-value recording of information can be performed.
[0233]
In addition, the magneto-optical recording medium, the recording / reproducing system, and the magnetic head device described in the above embodiments can be changed as needed without departing from the characteristics of the present invention. For example, it is possible to adopt a recording / reproducing method such as recording / reproducing information using a recording / reproducing apparatus including a magneto-optical head having a plurality of recording / reproducing laser light irradiation units.
[0234]
【The invention's effect】
As described above, according to the present invention, a higher density signal recording can be realized with a simpler layered structure of films. In the magneto-optical recording medium of the present invention, each recording state is extremely stable against fluctuations in the external magnetic field, and the magnetic characteristics of each recording layer, the laser beam intensity during recording and reproduction, and the external magnetic field intensity are finely matched. Since there is no need, a magneto-optical recording / reproducing system excellent in stability, mass productivity and practicality can be constructed.
[Brief description of the drawings]
FIG. 1 is a graph illustrating characteristics of a magneto-optical recording medium according to the present invention.
FIG. 2 is an explanatory diagram showing the principle of a multi-value recording method according to the present invention.
FIG. 3 is an explanatory diagram illustrating the relationship between the film configuration and the magnetization characteristics of the magneto-optical recording medium according to the present invention.
FIG. 4 is an explanatory diagram illustrating the relationship between the film configuration and the magnetization characteristics of the magneto-optical recording medium according to the present invention.
[Figure 5]Reference exampleIt is explanatory drawing which illustrates the relationship between the film | membrane structure of the magneto-optical recording medium which concerns on, and a magnetization characteristic.
FIG. 6 is an explanatory view illustrating the relationship between the film configuration and the magnetization characteristics of the magneto-optical recording medium according to the present invention.
FIG. 7 is an explanatory diagram illustrating the relationship between the film configuration and the magnetization characteristics of the magneto-optical recording medium according to the present invention.
FIG. 8 is an explanatory view illustrating the relationship between the film configuration and the magnetization characteristics of the magneto-optical recording medium according to the present invention.
FIG. 9 is an explanatory diagram of a magneto-optical recording medium according to a first configuration example.
FIG. 10 is a cross-sectional view of an essential part schematically showing a magneto-optical recording medium according to a first example.
FIG. 11 is a cross-sectional view schematically showing a main part of a magneto-optical recording medium according to a second embodiment.
FIG. 12 is a cross-sectional view schematically showing a main part of a magneto-optical recording medium according to a third embodiment.
FIG. 13 is a cross-sectional view of an essential part schematically showing a magneto-optical recording medium according to a fourth embodiment.
FIG. 14 is a cross-sectional view of an essential part schematically showing a magneto-optical recording medium according to a second configuration example.
FIG. 15 is an explanatory diagram showing a first example of a magnetic super-resolution reproduction method using a magneto-optical recording medium according to a second configuration example.
FIG. 16 is an explanatory diagram showing a second example of a magnetic super-resolution reproduction method using a magneto-optical recording medium according to a second configuration example.
FIG. 17 is an explanatory diagram showing a third example of the magnetic super-resolution reproduction method using the magneto-optical recording medium according to the second configuration example.
FIG. 18 is an explanatory diagram showing a fourth example of the magnetic super-resolution reproduction method using the magneto-optical recording medium according to the second configuration example.
FIG. 19 is a table showing the film structure of each magneto-optical recording medium included in the second configuration example.
FIG. 20 is an explanatory diagram of a preformat pattern formed on a sample servo type magneto-optical recording medium.
FIG. 21 is an explanatory diagram of the servo area in FIG. 20;
FIG. 22 is a diagram showing an example of a test area provided on a CAV optical disc.
FIG. 23 is a diagram showing an example of a test area provided on a ZCAV optical disc.
FIG. 24 is a block diagram of a convolutional encoder used for executing the multilevel recording method according to the first example.
FIG. 25 is an explanatory diagram showing a state transition of the output of the convolutional encoder in FIG. 24;
FIG. 26 is a configuration diagram of a multi-value recording / reproducing apparatus that executes a multi-value recording / reproducing method according to a first example.
FIG. 27 is an explanatory diagram showing a second example of the multi-level recording / reproducing system according to the present invention.
FIG. 28 is an explanatory diagram showing a signal modulation method of external magnetic field strength according to a second example of the multi-value recording / reproducing method.
FIG. 29 is a block diagram showing a first example of an external magnetic field intensity modulation circuit according to a second example of the multi-level recording / reproducing system.
FIG. 30 is a configuration diagram illustrating a second example of an external magnetic field intensity modulation circuit according to a second example of the multi-level recording / reproducing system.
FIG. 31 is an explanatory diagram showing a recording state of a magnetization domain recorded by the multi-value recording / reproducing method of the second example.
FIG. 32 is a circuit diagram showing an example of an external magnetic field application circuit.
33 is a block diagram of a signal reproducing circuit that reads a signal from the magneto-optical recording medium of FIG. 31. FIG.
FIG. 34 is an explanatory diagram showing the effect of the multi-level recording / reproducing system according to the second example.
FIG. 35 is a block diagram of a laser irradiation timing modulation circuit applied to a multilevel recording / reproducing system according to a third example.
36 is a timing chart showing the operation of the circuit of FIG. 35. FIG.
FIG. 37 is a configuration diagram of a signal reproduction circuit applied to a multi-level recording / reproducing system according to a third example.
38 is an operation explanatory diagram of the circuit of FIG. 37. FIG.
FIG. 39 is a configuration diagram of a laser intensity modulation circuit applied to a multi-level recording / reproducing system according to a fourth example.
40 is a timing chart showing the operation of the circuit of FIG. 39. FIG.
FIG. 41 is a configuration diagram of a signal reproduction circuit applied to a multi-level recording / reproducing system according to a fourth example.
42 is an operation explanatory diagram of the circuit of FIG. 41. FIG.
FIG. 43 is an explanatory diagram showing a first example of a combination of an applied magnetic field and an irradiation laser intensity applied to the fifth example of the multi-value recording / reproducing method.
FIG. 44 is an explanatory diagram showing a second example of a combination of an applied magnetic field and an irradiation laser intensity applied to the fifth example of the multilevel recording / reproducing method.
FIG. 45 is an explanatory diagram showing a third example of a combination of an applied magnetic field and an irradiation laser intensity applied to the fifth example of the multi-value recording / reproducing method.
FIG. 46 is a graph showing reproduction signal output characteristics of a magneto-optical recording medium applied to a sixth example of the multi-value recording / reproducing system.
FIG. 47 is an explanatory diagram of a multi-value recording / reproducing method belonging to the sixth example.
FIG. 48 is an explanatory diagram of another multilevel recording / reproducing system belonging to the sixth example.
FIG. 49 is an explanatory diagram of test signals according to a seventh example of the multi-level recording / reproducing system.
FIG. 50 is a configuration diagram of a test signal reproduction circuit according to a seventh example of the multi-value recording / reproduction method.
FIG. 51 is an explanatory diagram of a test signal according to an eighth example of the multi-value recording / reproducing method.
FIG. 52 is a configuration diagram of a test signal reproduction circuit according to a ninth example of the multi-value recording / reproduction method.
FIG. 53 is an explanatory diagram showing a tenth example of the multi-value recording / reproducing method.
FIG. 54 is an explanatory diagram showing a first example of a mark edge recording method belonging to the tenth example of the multi-value recording / reproducing system.
FIG. 55 is an explanatory diagram showing a second example of the mark edge recording method belonging to the tenth example of the multi-value recording / reproducing method.
FIG. 56 is an explanatory diagram showing a third example of the mark edge recording method belonging to the tenth example of the multi-value recording / reproducing method.
FIG. 57 is an explanatory diagram showing a fourth example of the mark edge recording method belonging to the tenth example of the multi-value recording / reproducing method.
FIG. 58 is an explanatory diagram showing a fifth example of the mark edge recording method belonging to the tenth example of the multi-value recording / reproducing method.
FIG. 59 is an explanatory diagram showing a sixth example of the mark edge recording method belonging to the tenth example of the multi-value recording / reproducing system.
FIG. 60 is an explanatory diagram showing an eleventh example of the multi-value recording / reproducing method.
FIG. 61 is an explanatory diagram showing a twelfth example of the multi-value recording / reproducing method.
FIG. 62 is a block diagram of a recording / reproducing apparatus suitable for a sample servo type magneto-optical recording medium.
63 is a circuit diagram of a DC level correction circuit applied to the recording / reproducing apparatus of FIG. 62. FIG.
FIG. 64 is an explanatory diagram showing a thirteenth example of the multi-value recording / reproducing method.
FIG. 65 is a block diagram showing an example of an optimum condition detection circuit applied to the multilevel recording / reproducing system in the thirteenth example.
FIG. 66 is an explanatory diagram showing a fourteenth example of the multi-value recording / reproducing method.
FIG. 67 is a block diagram showing an example of an optimum condition detection circuit applied to the multilevel recording / reproducing system in the fourteenth example.
FIG. 68 is an explanatory diagram showing a first example of a test signal recording method belonging to the fifteenth example of the multi-value recording / reproducing system.
FIG. 69 is an explanatory diagram showing a second example of the test signal recording method belonging to the fifteenth example of the multi-value recording / reproducing method.
70 is a waveform diagram showing a reproduced signal waveform of a test signal recorded by the method of FIG. 68. FIG.
71 is a waveform diagram showing a reproduced signal waveform of a test signal recorded by the method of FIG. 69. FIG.
FIG. 72 is a block diagram showing an optimum condition detection circuit applied to the multilevel recording / reproducing system in the fifteenth example.
FIG. 73 is an explanatory diagram showing a sixteenth example of the multi-value recording / reproducing method.
74 is an explanatory diagram showing a seventeenth example of the multi-value recording / reproducing method. FIG.
FIG. 75 is an explanatory diagram showing an effect of the multi-value recording / reproducing system according to the seventeenth example.
FIG. 76 is an explanatory diagram showing a first example of an on-pit recording method belonging to the eighteenth example of the multi-value recording / reproducing method.
FIG. 77 is an explanatory diagram showing a second example of the on-pit recording method belonging to the eighteenth example of the multilevel recording / reproducing method.
78 is an explanatory diagram showing a third example of the on-pit recording method belonging to the eighteenth example of the multi-value recording / reproducing method. FIG.
FIG. 79 is an explanatory diagram showing a fourth example of the on-pit recording method belonging to the eighteenth example of the multi-value recording / reproducing method.
FIG. 80 is an explanatory diagram showing a fifth example of the on-pit recording method belonging to the eighteenth example of the multi-value recording / reproducing method.
FIG. 81 is an explanatory diagram showing another example of the multi-value recording / reproducing system according to the present invention.
FIG. 82 is an explanatory diagram showing another example of the multi-level recording / reproducing method according to the present invention.
FIG. 83 is an explanatory diagram showing another example of the multi-level recording / reproducing system according to the present invention.
FIG. 84 is an explanatory diagram showing another example of the multi-value recording / reproducing method according to the present invention.
FIG. 85 is an explanatory diagram showing another example of the multi-level recording / reproducing method according to the present invention.
FIG. 86 is a configuration diagram showing a first example of a magnetic head device.
FIG. 87 is a configuration diagram showing a second example of the magnetic head device.
FIG. 88 is a structural diagram showing a third example of a magnetic head device.
FIG. 89 is a configuration diagram showing a fourth example of a magnetic head device.
90 is a structural diagram showing a fifth example of a magnetic head device. FIG.
FIG. 91 is a structural diagram showing a sixth example of a magnetic head device.
FIG. 92 is a structural diagram showing a seventh example of a magnetic head device.
FIG. 93 is a structural diagram showing an eighth example of a magnetic head device.
FIG. 94 is an explanatory diagram of the prior art.
FIG. 95 is an explanatory diagram of the prior art.
FIG. 96 is a graph illustrating the external magnetic field characteristics of the recording layer in which two recording states exist with respect to the external magnetic field.
FIG. 97 is a graph illustrating the external magnetic field characteristics of the recording layer in which one recording state exists with respect to the external magnetic field.
FIG. 98 is an explanatory diagram showing a first example of the multi-value recording principle of the magneto-optical recording medium according to the present invention.
FIG. 99 is an explanatory diagram showing a second example of the multi-value recording principle of the magneto-optical recording medium according to the present invention.
FIG. 100 is an explanatory diagram showing a third example of the multi-value recording principle of the magneto-optical recording medium according to the invention.
[Explanation of symbols]
1 Transparent substrate
2 Preformat pattern
3 First dielectric layer
4 First magnetic layer
4a Amorphous perpendicular magnetization film
4b Auxiliary magnetic film
5 Second dielectric layer
6 Second magnetic layer
7 Third dielectric layer
8 Reflective film
9 Protective film
11 Recording track
12 Data recording units
13 ID area
14 Servo area
15 Data area
16 Tracking pit
17 Test area
18 Clock pit
21 User area
22 Test area
201 First write signal sequence
202 Second write signal sequence
210 Reproducing laser beam
301 Prepit
302 Recording domain

Claims (6)

It has a plurality of magnetic layers laminated directly or via a nonmagnetic layer, and at least one of the plurality of magnetic layers is an amorphous alloy mainly composed of a rare earth and a transition metal. Thus, the sublattice magnetic moment of the rare earth atom is magnetically coupled to the perpendicularly magnetized film made of a ferrimagnetic material, which is dominant from the room temperature to the Curie temperature than the sublattice magnetic moment of the transition metal atom, and this perpendicularly magnetized film by exchange coupling. It consists of an auxiliary magnetic film made of a PtCo alloy, and when an external magnetic field is applied, it has a peak of change in the carrier wave of the optical modulation recording signal in two different magnetic field strength ranges. It has no film and is composed of a single perpendicularly magnetized film, and when an external magnetic field is applied , the peak of the change in the carrier wave of the optical modulation recording signal falls within one magnetic field strength range different from the one magnetic layer. A magneto-optical recording medium characterized in that a four-value signal can be directly overwritten as a whole by applying external magnetic fields having different magnetic field strengths in four stages . 2. The magneto-optical recording medium according to claim 1, wherein when the reproducing laser beam is irradiated on the reproducing laser beam incident side of at least one of the magnetic layers, the reproducing is applied to the magnetic layer. A magneto- optical recording medium , wherein an aperture forming layer for selectively forming an aperture smaller than the spot diameter of the laser beam for thermo-magnetic is provided . 3. The magneto-optical recording medium according to claim 2 , wherein a cutting layer is provided in contact with the hole forming layer . 2. The magneto-optical recording medium according to claim 1 , wherein the transition metal is at least one kind of transition metal element selected from [Co, Fe], and the rare earth is from [Tb, Gd, Dy, Nd]. A magneto-optical recording medium comprising at least one selected rare earth element . 2. The magneto-optical recording medium according to claim 1 , wherein the auxiliary magnetic film has a thickness adjusted to a range of 1 to 30 mm . 2. The magneto-optical recording medium according to claim 1, wherein the data recording area is divided into a plurality of data recording units, and each of the data recording units included in the multilevel recording signal recorded in the data recording unit is provided at the head portion of each data recording unit. A magneto-optical recording medium comprising a test area for setting a slice level of a signal .

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