JP3631194B2 - Method for manufacturing magneto-optical recording medium - Google Patents

Description

【００１６】
この力Ｆ_１ は、磁壁エネルギーの低い方に磁壁を移動させるように作用する。第１の磁性層は、磁壁抗磁力が小さく磁壁移動度が大きいので、単独では、この力Ｆ_１ によって容易に磁壁が移動する。しかし、位置ｘ_ｓ より手前（図では右側）の領域では、まだ媒体温度がＴ_ｓ より低く、磁壁抗磁力の大きな第３の磁性層と交換結合しているために、第３の磁性層中の磁壁の位置に対応した位置に第１の磁性層中の磁壁も固定されている。
【００１７】
本発明においては、図１（ａ）に示す様に、磁壁１５が媒体の位置ｘ_ｓ にあると、媒体温度が第２の磁性層のキュリー温度近傍の温度Ｔ_ｓ まで上昇し、第１の磁性層と第３の磁性層との間の交換結合が切断される。この結果、第１の磁性層中の磁壁１５は、破線矢印１７で示した様に、より温度が高く磁壁エネルギー密度の小さな領域へと“瞬間的”に移動する。
【００１８】
再生用の光ビームのスポット１６の下を磁壁１５が通過すると、スポット内の第１の磁性層の原子スピンは全て一方向に揃う。そして、媒体の移動に伴って磁壁１５が位置ｘ_ｓ に来る度に、スポットの下を磁壁１５が瞬間的に移動しスポット内の原子スピンの向きが反転して全て一方向に揃う。この結果、図１（ａ）に示す様に、再生信号振幅は記録されている磁壁の間隔（即ち記録マーク長）によらず、常に一定かつ最大の振幅になり、光学的な回折限界に起因した波形干渉等の問題から完全に解放されるのである。
【００１９】
但し、磁壁の移動速度は無限大ではないから、スポットの下を磁壁が通過するのに要する時間が、最短記録マーク長相当の距離を媒体が移動するのに要する時間ｔ_ｍｉｎ よりも長くならないようにする必要がある（図２参照）。
【００２０】
図３は、上述の原理作用による方法と、通常の従来法とを比較する模式図である。この図において（ａ１）〜（ａ７）、および（ｂ１）〜（ｂ７）は、記録マーク長の異なる磁区３３が形成された情報トラック３６上を、再生用スポット３１が移動する状態を示す。また（ａ８）および（ｂ８）は、得られる再生信号のグラフである。
【００２１】
従来の再生方法においては、再生用スポット３１自体が情報トラック３６上のひとつの磁区内に完全に入った状態（ｂ２）でないと、再生信号の最大振幅が得られない（ｂ８）。一方、本発明に適用する再生方法おいては、再生用スポット３１と温度プロファイルを同方向３２に相対移動させ、再生用スポット３１の直前部分が第２の磁性層の臨界温度Ｔ_ｓ になる様にしてある。したがって、再生用スポット３１が磁壁３４に差掛る直前において、磁壁３４の部分の温度が臨界温度Ｔｓとなり、磁壁３４が逆方向３５に移動し、再生用スポット３１が記録マーク内に完全に入った状態（ａ２）となり、瞬時に再生信号の最大振幅が得られる（ａ８）。
【００２２】
また従来の再生方法においては、磁区３３がスポット径よりも狭い場合には、再生用スポット３１全体が磁区内に納まらず（ｂ３〜ｂ７）、得られる再生信号も不明瞭となる（ｂ８）。一方、本発明に適用する再生方法においては、再生用スポット３１が記録マークの磁壁にほぼ差掛った段階で、磁壁が逆方向後方に逐次移動するので（ａ３〜ａ７）、極めて明瞭な再生信号が得られる（ａ８）。
【００２３】
以上、本発明により製造される第１の磁性層〜第３の磁性層を有する光磁気記録媒体について説明したが、本発明においては、図４に示す様に、第４の磁性層４４を第１の磁性層４１と第２の磁性層４２との間に設けてもよい。この第４の磁性層４４は、第２の磁性層よりも高く、該第１の磁性層よりも低いキュリー温度を有し、かつ少なくとも該第２の磁性層のキュリー温度以上の温度において、該第３の磁性層に比べて相対的に磁壁抗磁力が小さな垂直磁化膜からなるものである。この第４の磁性層は、更に第１の磁性層中の磁壁を移動させるのに充分な力を誘発するためのものである。
【００２４】
図４（ａ）（ｂ）に示す様に、この第４の磁性層を有する光磁気記録媒体においても同様に、位置ｘ_ｓ で第２の磁性層のキュリー温度近傍の温度Ｔ_ｓ とすることによって、第４の磁性層と第３の磁性層との間の交換結合を切断し、第１及び第４の磁性層中の磁壁を移動できる。
【００２５】
図４（ｃ）は、上述の温度分布に対応した第１の磁性層の磁壁エネルギー密度_１ および第４の磁性層の磁壁エネルギー密度_４ の分布を示すグラフである。この様にｘ方向に磁壁エネルギー密度_１ の勾配があると、先に説明したと同様に位置ｘに存在する各層の磁壁に対して力Ｆ_ｉ が作用し、この力Ｆ_ｉ は、磁壁エネルギーの低い方に磁壁を移動させるのである。
【００２６】
一方、記録を高速で読み出すためには、磁壁を高速で移動させる必要がある。そのために、磁壁に大きな力を作用させる必要がある。一般に、磁壁エネルギー密度の温度依存性は、キュリー温度に近づく程大きくなる。従って、キュリー温度近傍の温度範囲で温度勾配を与えた方が、ｘ方向の磁壁エネルギー密度の勾配を大きくすることができ、磁壁に大きな力を作用させることができる。しかし、第１の磁性層からの反射光の偏光面の変化を検出するためには、再生用の光ビームのスポットの照射領域においては、第１の磁性層のキュリー温度よりも充分に低い温度になっている必要がある。
【００２７】
ここで図４に示した様に、よりキュリー温度の低い第４の磁性層４４を、第１の磁性層の光ビームの入射側と反対側に隣接して設ければ、再生用の光ビームのスポットの照射領域において、第１の磁性層のキュリー温度よりは充分低く、かつ第４の磁性層のキュリー温度近傍の温度範囲で温度勾配を与えることができる。この結果、第４の磁性層中の磁壁に大きな力が作用し、第１の磁性層中の磁壁にも、第４の磁性層との交換相互作用による力が付加されて、大きな力が作用するのである。
【００２８】
また更に、第４の磁性層に、第２の磁性層に近づく程キュリー温度が低くなるような膜厚方向のキュリー温度の勾配をつければ、ｘ方向の温度勾配に伴って、ｘ方向に順次キュリー温度直下の第４の磁性層の構成部を形成できるので、磁壁を移動させる必要のあるｘ方向の範囲全般に渡って、比較的大きな力を作用させることが可能になる。
【００２９】
以下、本発明を適用した実施形態について図面を参照しながら説明する。
【００３０】
図５は、光磁気記録媒体の層構成の一実施態様を示す模式的断面図である。この態様においては、透明基板５６上に、誘電体層５５、第１の磁性層５１、第２の磁性層５２、第３の磁性層５３、誘電体層５４が順次積層されている。
【００３１】
透明基板５６としては、例えば、ポリカーボネート、ガラス等を用いることができる。誘電体層５５としては、例えば、Ｓｉ_３ Ｎ_４ 、ＡｌＮ、ＳｉＯ_２ 、ＳｉＯ、ＺｎＳ、ＭｇＦ_２ などの透明誘電材料が使用できる。最後に保護膜として再び形成される誘電体層５４も同様のものを用いることができる。これら各層は、例えばマグネトロンスパッタ装置による連続スパッタリング、または連続蒸着等によって被着形成できる。特に各磁性層は、真空を破ることなく連続成膜されることで、互いに交換結合をしている。
【００３２】
また、この構成に、更にＡｌ、ＡｌＴａ、ＡｌＴｉ、ＡｌＣｒ、Ｃｕなどからなる金属層を付加して、熱的な特性を調整してもよい。また、高分子樹脂からなる保護コートを付与してもよい。あるいは、成膜後の基板を貼り合わせてもよい。
【００３３】
上記媒体において、各磁性層５１〜５３は、種々の磁性材料によって構成することが考えられるが、例えば、Ｐｒ、Ｎｄ、Ｓｍ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏなどの希土類金属元素の一種類あるいは二種類以上が１０〜４０ａｔ％と、Ｆｅ、Ｃｏ、Ｎｉなどの鉄族元素の一種類あるいは二種類以上が９０〜６０ａｔ％とで構成される希土類−鉄族非晶質合金によって構成し得る。また、耐食性向上などのために、これにＣｒ、Ｍｎ、Ｃｕ、Ｔｉ、Ａｌ、Ｓｉ、Ｐｔ、Ｉｎなどの元素を少量添加してもよい。
【００３４】
重希土類−鉄族非晶質合金の場合、飽和磁化は、希土類元素と鉄族元素との組成比により制御することが可能である。また、キュリー温度も、組成比により制御することが可能であるが、飽和磁化と独立に制御するためには、鉄族元素として、Ｆｅの一部をＣｏで置き換えた材料を用い、置換量を制御する方法がより好ましく利用できる。即ち、Ｆｅ １ａｔ％をＣｏで置換することにより、６℃程度のキュリー温度上昇が見込めるので、この関係を用いて所望のキュリー温度となるようにＣｏの添加量を調整する。また、Ｃｒ、Ｔｉなどの非磁性元素を微量添加することにより、逆にキュリー温度を低下させることも可能である。あるいはまた、二種類以上の希土類元素を用いてそれらの組成比を調整することでもキュリー温度を制御できる。
【００３５】
この他に、ガーネット、白金族−鉄族周期構造膜、もしくは白金族−鉄族合金などの材料も使用可能である。
【００３６】
第１の磁性層としては、例えば、ＧｄＣｏ、ＧｄＦｅＣｏ、ＧｄＦｅ、ＮｄＧｄＦｅＣｏなどの垂直磁気異方性の小さな希土類−鉄族非晶質合金や、ガーネット等のバブルメモリ用材料が望ましい。
【００３７】
第３の磁性層としては、例えば、ＴｂＦｅＣｏ、ＤｙＦｅＣｏ、ＴｂＤｙＦｅＣｏなどの希土類−鉄族非晶質合金や、Ｐｔ／Ｃｏ、Ｐｄ／Ｃｏなどの白金族−鉄族周期構造膜など、垂直磁気異方性が大きく安定に磁化状態が保持できるものが望ましい。
【００３８】
光磁気記録媒体へのデータ信号の記録は、媒体を移動させながら、第３の磁性層がキュリー温度以上になるようなパワーのレーザー光を照射しながら外部磁界を変調して行うか、もしくは一定方向の磁界を印加しながらレーザーパワーを変調して行う。後者の場合、光スポット内の所定領域のみが第３の磁性層のキュリー温度近傍になる様にレーザー光の強度を調整すれば、光スポットの径以下の記録磁区が形成でき、その結果、光の回折限界以下の周期の信号を記録できる。
【００３９】
更に、第４の磁性層を設けた媒体の構成を図６に示す。この態様においては、透明基板６６上に、誘電体層６５、第１の磁性層６１、第４の磁性層６４、第２の磁性層６２、第３の磁性層６３、誘電体層６４が順次積層されている。各層の材料、製造法等に関しては、図５について述べたものと同様である。
【００４０】
【実施例】
以下に、実施例及び参考例をもって本発明を更に詳細に説明するが、本発明はその要旨を越えない限り以下の実施例に限定されるものではない。
【００４１】
まず、図５に示した様な第１〜第３の磁性層を有する光磁気記録媒体の参考例及び実施例を以下に挙げる。
【００４２】
＜参考例１＞
直流マグネトロンスパッタリング装置に、ＢドープしたＳｉ、及びＧｄ、Ｄｙ、Ｔｂ、Ｆｅ、Ｃｏの各ターゲットを取り付け、トラッキング用の案内溝の形成されたポリカーボネイト基板を基板ホルダーに固定した後、１×１０^-5Ｐａ以下の高真空になるまでチャンバー内をクライオポンプで真空排気した。真空排気をしたままＡｒガスを０．３Ｐａとなるまでチャンバー内に導入し、基板を回転させながら、干渉層であるＳｉＮ層を８００オングストローム成膜した。引き続き、第１の磁性層としてＧｄＣｏ層を３００オングストローム、第２の磁性層としてＤｙＦｅ層を１００オングストローム、第３の磁性層としてＴｂＦｅＣｏ層を４００オングストローム順次成膜した。最後に、保護層としてＳｉＮ層を８００オングストローム成膜した。ＳｉＮ層成膜時にはＡｒガスに加えてＮ₂ ガスを導入し、直流反応性スパッタにより成膜した。各磁性層は、Ｇｄ、Ｄｙ、Ｔｂ、Ｆｅ、Ｃｏの各ターゲットに直流パワーを印加して成膜した。
【００４３】
各磁性層の組成は、全て補償組成近傍になるように調整し、キュリー温度は、第１の磁性層が３００℃以上、第２の磁性層が７０℃、第３の磁性層が２００℃程度となるように設定した。
【００４４】
この媒体は、図７（ａ）に断面形状で示した様に、基板７１上に、誘電体層７２、磁性層７３、誘電体層７４が積層され、基板７１の案内溝を深さ１０００オングストロームの矩形に形成してある。このため、ランド７６上に積層された磁性層７２は、案内溝７５の部分でほぼ分離されている。なお実際には、段差部にも多少膜が堆積して磁性層が繋がってしまうが、他の部分と比較して膜厚が非常に薄くなるので、段差部での結合は無視できる。本発明において、各情報トラック間で互いに磁気的に分離されるとは、この様な状態も含まれる。このランド７６上に幅いっぱいに反転磁区を形成すると、図７（ｂ）に示す様に、ランド７６上の磁区の境界部に、閉じていない磁壁７７が形成される。このような磁壁７７は、トラック方向に移動させても、トラック側部の磁壁７７の生成・消滅を伴わないので、容易に移動させることができる。
【００４５】
この様にして得た光磁気記録媒体について、記録再生特性を測定した。
【００４６】
測定に用いた記録再生装置には、図８に示すように、一般的な光磁気ディスク記録再生装置の光学系に、加熱用のレーザーが付加されている。８１は、記録再生用のレーザー光源で、波長は７８０ｎｍで、記録媒体に対してＰ偏向が入射する様に配置されている。８２は、加熱用のレーザー光源で、波長は１．３ｍで、同じく記録媒体に対してＰ偏向が入射する様に配置されている。８３は、７８０ｎｍ光を１００％透過し、１．３ｍ光を１００％反射するように設計されたダイクロイックミラーである。８４は、偏向ビームスプリッタで、７８０ｎｍ光、１．３ｍ光、各々のＰ偏向は７０〜８０％透過し、Ｓ偏向は１００％反射するよう設計されている。１．３ｍ光の光束径は、対物レンズ８５の開口径よりも小さくなるようにしてあり、全開口部を通過して集光される７８０ｎｍ光に比べて、ＮＡが小さくなるようにしてある。また、８７は、１．３ｍ光が、信号検出系に漏れ込まないようにするために設けるもので、７８０ｎｍ光を１００％透過し、１．３ｍ光を１００％反射するように設計されたダイクロイックミラーである。
【００４７】
この光学系により、記録媒体８６の記録面上に、図９（ａ）に示すように、案内溝９４間のランド９５上において、記録再生用のスポット９１と、加熱用のスポット９２とを結像させることができる。加熱用のスポット９２は、波長が長くＮＡが小さいので、記録再生用のスポット９１よりも径が大きくなる。これにより、移動している媒体の記録面上の記録再生用のスポット９１の領域に、図９（ｂ）に示してあるような所望の温度勾配を容易に形成することができる。ここで温度Ｔ_ｓ の等温線９６も図示する。記録再生は媒体を線速５ｍ／ｓｅｃで駆動して行なった。
【００４８】
まず、記録再生用レーザーを８ｍＷでＤＣ照射しながら磁界を１５０ Ｏｅで変調することにより、第３の磁性層のキュリー温度以上に加熱した後の冷却過程で、磁界の変調に対応した上向き磁化と下向き磁化との繰り返しパターンを形成した。尚、この時、加熱用のレーザーを合わせて照射して、記録再生用レーザーの記録パワーを低減させることも可能である。
【００４９】
記録磁界の変調周波数は１〜１０ＭＨｚまで変化させ、２．５〜０．２５ｍの範囲のマーク長のパターンを記録した。
【００５０】
再生時の記録再生用のレーザーのパワーは１ｍＷとし、加熱用のレーザーを２０ｍＷのパワーで同時に照射しながら、各マーク長のパターンについてＣ／Ｎを測定した。この時の媒体面上の温度分布は図９（ｂ）に示すとおりである。
【００５１】
この測定結果を図１０のグラフ線ａに示す。また比較のため同図中の特開平３−９３０５８号に記載の従来の超解像再生方法による測定結果をグラフ線ｂとして示し、超解像現象の起こらない通常の再生方法による測定結果をグラフ線ｃとして示す。
【００５２】
この再生方法によると、マーク長が短くなっても再生用のスポット内の全磁化の反転が検出されるので、光の回折限界以下の周期の信号が再生可能となるのみならず、Ｃ／Ｎのマーク長依存性がほとんどなくなる。
【００５３】
尚、本参考例の媒体において、第１の磁性層の磁壁が、温度勾配によって移動する様子は、以下に述べるように、偏光顕微鏡による直接観察で確認された。
【００５４】
まず、参考例１と同様の構成で、磁性層の積層順を逆にしたサンプルを作製した。このサンプルに参考例１と同様の記録方法により、磁区パターンを形成した。これを膜面側、即ち第１の磁性層側から偏光顕微鏡で観察した。
【００５５】
次に、このサンプルに加熱用の集光レーザーを照射して、偏光顕微鏡の視野内で、参考例１とほぼ同様の温度分布を形成した。
【００５６】
この状態で、サンプルに５００ Ｏｅ 程度の磁界を印加した。この結果、温度分布に対応した円形の領域のみが、外部磁界の方向に配向するのが観察された。これは、この領域において、第１の磁性層と第３の磁性層との間の交換結合が切断されていることを意味している。
【００５７】
次に、磁界の印加を停止して、トラック方向にサンプルをゆっくりと移動させた。すると、トラック上に形成されている磁区の境界部が上述の円形の結合切断領域に入る度に、移動してきた磁区が円形領域の中心方向に向かって拡大するのが観察された。
【００５８】
加熱用のレーザーの照射を停止すると、第３の磁性層に保存されていた磁区パターンが第１の磁性層に転写されるのが観察された。
【００５９】
以上より、第３の磁性層との結合が切断された領域において、第１の磁性層の磁壁が、温度勾配によって高温側へ移動することが確認された。
【００６０】
＜参考例２＞
参考例１と同様の成膜機、成膜方法で、同様にポリカーボネイト基板上に薄膜を成膜して光磁気記録媒体を作成した。但し、本参考例においては、以下の三点を変更した。
【００６１】
第一に、成膜前の基板表面にＡｒイオンの加速照射処理を加えたこと、第二に、干渉層であるＳｉＮ層を成膜した後の膜表面にＡｒイオンの加速照射処理を加えたことである。これらの処理により、表面状態を平滑化した。更に、第三に、第１の磁性層の膜厚を２０００オングストロームに変更したことである。これらの変更点は、それぞれ独立に、第１の磁性層の磁壁移動度の向上に寄与する。
【００６２】
この媒体の記録再生特性を参考例１と同様の方法で測定したところ、参考例１と同様の良好な結果が得られた。更に、再生時の媒体の線速度を２０ｍ／ｓｅｃまで高速化して再生しても、再生特性は低下しなかった。
【００６３】
＜実施例１＞
参考例１と同様の成膜機、成膜方法で、同様にポリカーボネイト基板上に薄膜を成膜して光磁気記録媒体を作製した。
【００６４】
但し、本実施例においては、基板として、プレピットが形成されており、案内溝の断面形状がＵ型になっているものを用いた。このため、積層した磁性層は、案内溝の部分で形状的に分断されていない。
【００６５】
この媒体の、案内溝の部分に高出力のレーザーを照射し、案内溝の部分の磁性層を全面にアニールした。この結果、案内溝の部分の磁性層が変質して面内膜になり、案内溝を介して、互いに隣接するトラックの磁性層の間の結合が分断された。この媒体の記録再生特性を参考例１と同様の方法で測定したところ、参考例１と同様の良好な結果が得られた。
【００６６】
また、上述のアニール処理を施さずに、上記の媒体の記録再生特性を参考例１と同様の方法で測定したところ、参考例１の結果に比べてノイズが上昇したが、光の回折限界以下の周期の信号の再生は、十分可能であった。この媒体では、閉じた磁壁で囲まれた磁区が存在するので、この磁区を拡大させる方向に磁壁を移動させる時に動作が不安定になりノイズが上昇した。
【００６７】
なお、隣接するトラックの磁性層との間の結合を分断する別の方法として、エッチング処理によるパターニングを行ってもよい。
【００６８】
＜比較例１＞
参考例１の媒体を用いて、加熱用のレーザーが付加されていない通常の光磁気ディスク記録再生装置によって、記録再生特性を測定した。
【００６９】
加熱用のレーザーが照射されていない他は、参考例１と同様の方法で再生特性を調べたところ、再生パワーを３ｍＷ程度まで増大させることにより、良好なＣ／Ｎが得られた。但し、参考例１の結果と比較すると、各マーク長において、５ｄＢ程度Ｃ／Ｎが低かった。これは、再生用スポットの前部においては媒体の温度が上昇しないので、再生用スポットの途中から磁壁の移動が起こり、参考例１のようには、スポット全域を有効に使用できないためである。
【００７０】
次に、図６に示した様な第１〜第４の磁性層を有する光磁気記録媒体の参考例及び実施例を以下に挙げる。
【００７１】
＜参考例３＞
直流マグネトロンスパッタリング装置に、ＢドープしたＳｉ、及びＧｄ、Ｔｂ、Ｆｅ、Ｃｏ、Ｃｒの各ターゲットを取り付け、トラッキング用の案内溝の形成されたポリカーボネイト基板を基板ホルダーに固定した後、１×１０^-5Ｐａ以下の高真空になるまでチャンバー内をクライオポンプで真空排気した。
【００７２】
真空排気をしたままＡｒガスを０．３Ｐａとなるまでチャンバー内に導入し、基板を回転させながら、干渉層であるＳｉＮ層を８００オングストローム成膜した。引き続き、第１の磁性層としてＧｄＣｏＣｒ層を３００オングストローム、第４の磁性層としてＧｄＦｅＣｒ層を３００オングストローム、第２の磁性層としてＴｂＦｅＣｒ層を１００オングストローム、第３の磁性層としてＴｂＦｅＣｏ層を４００オングストローム順次成膜した。最後に、保護層としてＳｉＮ層を８００オングストローム成膜した。ＳｉＮ層成膜時にはＡｒガスに加えてＮ_２ ガスを導入し、直流反応性スパッタにより成膜した。各磁性層は、Ｇｄ、Ｔｂ、Ｆｅ、Ｃｏ、Ｃｒの各ターゲットに直流パワーを印加して成膜した。
【００７３】
各磁性層の組成は、全て補償組成近傍になるように調整し、キュリー温度は、第１の磁性層が３００℃以上、第４の磁性層が１７０℃、第２の磁性層が７０℃、第３の磁性層が２００℃程度となるように設定した。この媒体は、参考例１と同様に、図７に示した様な断面形状を有する。
【００７４】
この様にして得た光磁気記録媒体について、参考例１と同様にして記録再生特性を測定した。ただし、記録時のＤＣ照射レーザーパワーは１０ｍＷとし、再生時の加熱用レーザーパワーは２５ｍＷとした。この測定結果は、参考例１と同様に、図１０のグラフ線ａの良好な結果が得られた。
【００７５】
また更に、再生時の媒体の線速度を２０ｍ／ｓｅｃまで高速化して再生しても再生特性は低下しなかった。
【００７６】
尚、第１の磁性層の磁壁が、温度勾配によって移動する様子は、参考例１と同様に偏光顕微鏡による直接観察で確認された。
【００７７】
＜実施例２＞
参考例３と同様の成膜機、成膜方法で、同様にポリカーボネイト基板上に薄膜を成膜して光磁気記録媒体を作成した。
【００７８】
但し、本実施例においては、基板として、プレピットが形成されており、案内溝の断面形状がＵ型になっているものを用いた。このため、積層した磁性層は、案内溝の部分で形状的に分断されていない。
【００７９】
磁性層その他の構成は、第４の磁性層の組成比を次に述べるように変化させた他は、参考例３と同様にした。
【００８０】
第４の磁性層は、ＧｄＦｅＣｒのＧｄの組成比を調整して、室温において鉄族元素副格子磁化優勢な組成にしたサンプル（１）と、室温において希土類元素副格子磁化優勢で、キュリー温度以下の温度に補償温度が存在する組成にしたサンプル（２）と、室温において希土類元素副格子磁化優勢で、キュリー温度以下の温度に補償温度が存在しない組成にしたサンプル（３）とを作製した。各サンプルのキュリー温度は、Ｃｒ添加量を調整して、全て１７０℃に合わせた。
【００８１】
これらのサンプルの、案内溝の部分に高出力のレーザーを照射し、案内溝の部分の磁性層を全面アニールした。この結果、案内溝の部分の磁性層が磁気的に変質し、案内溝を介して互いに隣接するトラックの磁性層の間の結合が分断された。
【００８２】
次に、記録再生特性を参考例３と同様の方法で測定したところ、線速５ｍ／ｓｅｃにおいて、各サンプルとも参考例２と同様の良好な結果が得られた。
【００８３】
しかし、線速を３０ｍ／ｓｅｃまで高速化して再生すると、サンプル（１）では、Ｃ／Ｎが５ｄＢ程度低下した。これに対し、サンプル（２）では、Ｃ／Ｎの低下はほとんど見られず、また、サンプル（３）では、２ｄＢ程度しか低下しなかった。
【００８４】
これは、室温において、希土類元素副格子磁化優勢な組成のもの、中でもキュリー温度以下に補償温度を有する組成のものの方が、キュリー温度近傍における、磁壁エネルギーの温度依存性が大きく、温度勾配によって、より大きな力を磁壁に作用させることができるためであると考えられる。
【００８５】
以上挙げた実施例に本発明は限定定されるものでない。他の実施可能な例として、光ヘッドは従来のままにして、媒体上の温度分布を別の手段でつい調整する方法も考えられる。例えば、磁界変調記録に用いる浮上ヘッドのコアを熱源として流用したり、その他適当な発熱体を媒体の再生用レーザー照射領域の近くに配置することが考えられる。但し、この場合、磁壁の移動開始位置となる温度の位置と、再生用スポットとの位置関係が再生信号の周波数に近い周波数で変動することがないように注意する必要がある。
【００８６】
【発明の効果】
以上詳細に説明したように、本発明によれば、再生信号振幅を低下させることなく光の回折限界以下の周期の信号が高速で再生可能となり、記録密度並びに転送速度を大幅に向上でき、再生装置の小型化も可能な光磁気記録媒体を製造できる。
【図面の簡単な説明】
【図１】本発明により製造した第１〜第３の磁性層を有する光磁気記録媒体を使用した場合の再生方法の概念を模式的に示した図である。（ａ）は、再生状態における媒体の断面を示し、各磁性層のスピンの配向状態を模式的に示してある。（ｂ）は、（ａ）に示されている位置における媒体上の温度分布を示している。（ｃ）は、同様の位置における磁壁エネルギー密度の分布及びそれに伴って磁壁に作用する力の分布を模式的に示している。
【図２】スポットの下を磁壁が通過するのに要する時間と、最短記録マーク長相当の距離を媒体が移動するのに要する時間ｔ_ｍｉｎ との関係を示すグラフである。
【図３】本発明に適用する再生方法と通常の従来法とを比較する模式図である。
【図４】第１〜第４の磁性層を有する光磁気記録媒体を使用した場合の再生方法の概念を模式的に示した図である。
【図５】本発明により製造する光磁気記録媒体の層構成の一実施態様を示す模式的断面図である。
【図６】本発明により製造する光磁気記録媒体の層構成の一実施態様を示す模式的断面図である。
【図７】実施例及び参考例における光磁気記録媒体の断面形状を示す図である。
【図８】実施例及び参考例において用いた記録再生装置を示す模式図である。
【図９】実施例及び参考例における再生状態を示す模式図である。
【図１０】参考例において得られたＣ／Ｎを示すグラフである。
【符号の説明】
１１ 第１の磁性層
１２ 第２の磁性層
１３ 第３の磁性層
１４ 原子スピンの向き
１５ 磁壁
１６ 再生様の光ビームスポット
１７ 磁壁の移動方向
１８ 媒体の移動方向[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a magneto-optical recording medium or the like that records and reproduces information by laser light using a magneto-optical effect, and more particularly, a method for manufacturing a magneto-optical recording medium that enables high-density recording of the medium. About.
[0002]
[Prior art]
As a rewritable high-density recording method, a magneto-optical recording medium that uses magnetic energy of a semiconductor laser to write information on a magnetic thin film, records information, and reads out the information using a magneto-optic effect has attracted attention. . In recent years, there has been an increasing demand for a recording medium having a larger capacity by increasing the recording density of the magneto-optical recording medium.
[0003]
The linear recording density of an optical disk such as a magneto-optical recording medium greatly depends on the laser wavelength of the reproducing optical system and the numerical aperture of the objective lens. That is, if the laser wavelength of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the diameter of the beam waist is determined, and therefore, the spatial frequency at the time of signal reproduction is limited to about 2 NA / detectable.
[0004]
Therefore, in order to realize high density in the conventional optical disc, it is necessary to shorten the laser wavelength of the reproducing optical system and increase the numerical aperture NA of the objective lens. However, there is a limit in improving the laser wavelength and the numerical aperture of the objective lens. For this reason, a technique for improving the recording density by devising the configuration of the recording medium and the reading method has been developed.
[0005]
For example, in Japanese Patent Laid-Open No. 3-93058, signal recording is performed on a recording and holding layer of a multilayer film having a reproducing layer and a recording and holding layer that are magnetically coupled, and the magnetization direction of the reproducing layer is changed. There has been proposed a signal reproduction method in which after the alignment, the laser beam is irradiated and heated to read the signal recorded on the recording holding layer while transferring it to the temperature rising region of the reproduction layer.
[0006]
According to this method, the area where the signal is detected by reaching the transfer temperature by the laser with respect to the spot diameter of the reproducing laser can be limited to a smaller area. As a result, a signal having a period less than the diffraction limit of light can be reproduced.
[0007]
[Problems to be solved by the invention]
However, in the magneto-optical reproduction method described in Japanese Patent Laid-Open No. 3-93058, since the signal detection area that is effectively used becomes smaller with respect to the spot diameter of the laser for reproduction, the reproduction signal amplitude is greatly reduced, which is sufficient. There is a disadvantage that a stable reproduction output cannot be obtained.
[0008]
In addition, the magnetization of the reproducing layer must be aligned in one direction before the laser beam is irradiated. Therefore, it is necessary to add an initialization magnet for the reproduction layer to the conventional apparatus. For this reason, the reproducing method has problems such that the magneto-optical recording apparatus becomes complicated, the cost increases, and it is difficult to reduce the size.
[0009]
The present invention has been made to solve such problems of the prior art. That is, it is an object of the present invention to be able to reproduce a signal having a period less than the diffraction limit of light at a high speed without lowering the reproduction signal amplitude, greatly improving the recording density and transfer speed, and reducing the size of the reproduction apparatus. An object of the present invention is to provide a method for manufacturing a magneto-optical recording medium.
[0010]
[Means for Solving the Problems]
The above purpose is Information generated on the recording medium is reproduced by moving the domain wall of the recording magnetic domain by the force generated due to the gradient of the temperature distribution formed on the recording medium. In the method of manufacturing a magneto-optical recording medium, on the substrate, at least a first magnetic layer that contributes to reproducing information and a domain wall moves, a third magnetic layer that holds a recording magnetic domain according to information, and A second magnetic layer that is disposed between the first magnetic layer and the third magnetic layer and has a Curie temperature lower than the two layers is referred to as the first magnetic layer, the second magnetic layer, and the third magnetic layer. The step of depositing the layers in sequence, and irradiating high-power laser light between the adjacent information tracks to alter the magnetic layer existing between the information tracks, thereby changing the magnetic layer between the magnetic layers of the adjacent information tracks. The method can be achieved by a method for manufacturing a magneto-optical recording medium, which includes an annealing step for breaking a typical bond.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram for explaining the operation of a magneto-optical recording medium manufactured according to the present invention and its reproducing method.
[0012]
FIG. 1A is a schematic cross-sectional view of a magneto-optical recording medium. The magnetic layer of this medium is formed by sequentially laminating a first magnetic layer 11, a second magnetic layer 12, and a third magnetic layer 13. Arrows 14 in each layer indicate the direction of atomic spin. A domain wall 15 is formed at the boundary between regions where spin directions are opposite to each other. The recording signal of this recording layer is also shown as a graph on the lower side.
[0013]
FIG. 1B is a graph showing the temperature distribution formed on the magneto-optical recording medium. This temperature distribution may be induced on the medium by the light beam irradiated for reproduction itself, but preferably, another heating means is used in combination with the temperature from the front side of the spot of the light beam for reproduction. And a temperature distribution is formed such that a temperature peak comes behind the spot. Where position x _s , The medium temperature is a temperature T near the Curie temperature of the second magnetic layer. _s It has become.
[0014]
FIG. 1C shows the domain wall energy density of the first magnetic layer corresponding to the temperature distribution of FIG. ₁ It is a graph which shows distribution of. In this way, the domain wall energy density in the x direction ₁ , The force F obtained from the following equation with respect to the domain wall of each layer existing at the position x: ₁ Works.
[0015]
[Expression 1]

[0016]
This force F ₁ Acts to move the domain wall to the lower domain wall energy. The first magnetic layer has a small domain wall coercive force and a large domain wall mobility. ₁ The domain wall moves easily. However, position x _s In the region closer to the front (right side in the figure), the medium temperature is still T _s Since it is exchange coupled with the third magnetic layer having a lower magnetic wall coercive force, the domain wall in the first magnetic layer is also fixed at a position corresponding to the position of the domain wall in the third magnetic layer. .
[0017]
In the present invention, as shown in FIG. 1A, the domain wall 15 is positioned at the position x of the medium. _s The medium temperature is a temperature T near the Curie temperature of the second magnetic layer. _s And the exchange coupling between the first magnetic layer and the third magnetic layer is broken. As a result, the domain wall 15 in the first magnetic layer moves “instantaneously” to a region where the temperature is higher and the domain wall energy density is smaller, as indicated by the broken arrow 17.
[0018]
When the domain wall 15 passes under the spot 16 of the reproducing light beam, all the atomic spins of the first magnetic layer in the spot are aligned in one direction. As the medium moves, the domain wall 15 moves to the position x. _s Each time, the domain wall 15 instantaneously moves under the spot, the direction of the atomic spin in the spot is reversed, and all are aligned in one direction. As a result, as shown in FIG. 1A, the reproduction signal amplitude is always constant and maximum regardless of the recorded domain wall interval (that is, the recording mark length), which is caused by the optical diffraction limit. It is completely free from problems such as waveform interference.
[0019]
However, since the moving speed of the domain wall is not infinite, the time required for the domain wall to pass under the spot is the time t required for the medium to move the distance corresponding to the shortest recording mark length. _min (See FIG. 2).
[0020]
FIG. 3 is a schematic diagram for comparing the above-described principle-based method with a normal conventional method. In this figure, (a1) to (a7) and (b1) to (b7) show a state in which the reproduction spot 31 moves on the information track 36 on which the magnetic domains 33 having different recording mark lengths are formed. Further, (a8) and (b8) are graphs of the obtained reproduction signal.
[0021]
In the conventional reproducing method, unless the reproducing spot 31 itself is completely in one magnetic domain on the information track 36 (b2), the maximum amplitude of the reproduced signal cannot be obtained (b8). On the other hand, in the reproducing method applied to the present invention, the reproducing spot 31 and the temperature profile are relatively moved in the same direction 32, and the portion immediately before the reproducing spot 31 is the critical temperature T of the second magnetic layer. _s It is made to become. Therefore, immediately before the reproduction spot 31 approaches the domain wall 34, the temperature of the domain wall 34 becomes the critical temperature Ts, the domain wall 34 moves in the reverse direction 35, and the reproduction spot 31 completely enters the recording mark. The state (a2) is reached, and the maximum amplitude of the reproduction signal is obtained instantaneously (a8).
[0022]
Further, in the conventional reproducing method, when the magnetic domain 33 is narrower than the spot diameter, the entire reproducing spot 31 does not fit in the magnetic domain (b3 to b7), and the obtained reproduced signal is also unclear (b8). On the other hand, in the reproducing method applied to the present invention, the magnetic wall sequentially moves backward in the reverse direction at the stage where the reproducing spot 31 almost approaches the magnetic wall of the recording mark (a3 to a7). Is obtained (a8).
[0023]
The magneto-optical recording medium having the first to third magnetic layers manufactured according to the present invention has been described above. However, in the present invention, as shown in FIG. The magnetic layer 41 may be provided between the first magnetic layer 41 and the second magnetic layer 42. The fourth magnetic layer 44 has a Curie temperature higher than that of the second magnetic layer and lower than that of the first magnetic layer, and at least at a temperature equal to or higher than the Curie temperature of the second magnetic layer. It is made of a perpendicular magnetization film having a relatively small domain wall coercive force as compared with the third magnetic layer. The fourth magnetic layer is for inducing a force sufficient to move the domain wall in the first magnetic layer.
[0024]
Similarly, in the magneto-optical recording medium having the fourth magnetic layer, as shown in FIGS. _s The temperature T near the Curie temperature of the second magnetic layer _s By so doing, the exchange coupling between the fourth magnetic layer and the third magnetic layer can be cut, and the domain walls in the first and fourth magnetic layers can be moved.
[0025]
FIG. 4C shows the domain wall energy density of the first magnetic layer corresponding to the above temperature distribution. ₁ And the domain wall energy density of the fourth magnetic layer ₄ It is a graph which shows distribution of. In this way, the domain wall energy density in the x direction ₁ If there is a gradient, a force F is applied to the domain wall of each layer existing at the position x as described above. _i Acts and this force F _i Moves the domain wall to the lower domain wall energy.
[0026]
On the other hand, in order to read the recording at high speed, it is necessary to move the domain wall at high speed. Therefore, it is necessary to apply a large force to the domain wall. In general, the temperature dependence of the domain wall energy density increases as the temperature approaches the Curie temperature. Therefore, when the temperature gradient is applied in the temperature range near the Curie temperature, the gradient of the domain wall energy density in the x direction can be increased, and a large force can be applied to the domain wall. However, in order to detect a change in the plane of polarization of the reflected light from the first magnetic layer, a temperature sufficiently lower than the Curie temperature of the first magnetic layer in the irradiation region of the reproduction light beam spot. It is necessary to become.
[0027]
Here, as shown in FIG. 4, if the fourth magnetic layer 44 having a lower Curie temperature is provided adjacent to the light beam incident side of the first magnetic layer, the light beam for reproduction is provided. In the spot irradiation region, a temperature gradient can be given in a temperature range sufficiently lower than the Curie temperature of the first magnetic layer and in the vicinity of the Curie temperature of the fourth magnetic layer. As a result, a large force acts on the domain wall in the fourth magnetic layer, and a force due to the exchange interaction with the fourth magnetic layer is also applied to the domain wall in the first magnetic layer. To do.
[0028]
Furthermore, if a Curie temperature gradient in the film thickness direction is applied to the fourth magnetic layer such that the Curie temperature becomes lower as the second magnetic layer is approached, the x magnetic layer is sequentially moved in the x direction along with the temperature gradient in the x direction. Since the constituent part of the fourth magnetic layer immediately below the Curie temperature can be formed, a relatively large force can be applied over the entire range in the x direction where the domain wall needs to be moved.
[0029]
Embodiments to which the present invention is applied will be described below with reference to the drawings.
[0030]
FIG. 5 is a schematic cross-sectional view showing one embodiment of the layer structure of the magneto-optical recording medium. In this embodiment, a dielectric layer 55, a first magnetic layer 51, a second magnetic layer 52, a third magnetic layer 53, and a dielectric layer 54 are sequentially stacked on the transparent substrate 56.
[0031]
As the transparent substrate 56, for example, polycarbonate, glass, or the like can be used. As the dielectric layer 55, for example, Si ₃ N ₄ , AlN, SiO ₂ , SiO, ZnS, MgF ₂ A transparent dielectric material such as can be used. Finally, the same dielectric layer 54 that is formed again as a protective film can be used. These layers can be formed by, for example, continuous sputtering using a magnetron sputtering apparatus or continuous vapor deposition. In particular, the magnetic layers are exchange-coupled to each other by being continuously formed without breaking the vacuum.
[0032]
In addition, a metal layer made of Al, AlTa, AlTi, AlCr, Cu or the like may be added to this configuration to adjust the thermal characteristics. Moreover, you may provide the protective coat which consists of polymer resins. Alternatively, a substrate after film formation may be bonded.
[0033]
In the above medium, each of the magnetic layers 51 to 53 may be composed of various magnetic materials. For example, one or two rare earth metal elements such as Pr, Nd, Sm, Gd, Tb, Dy, and Ho are used. It can be constituted by a rare earth-iron group amorphous alloy composed of 10 to 40 at% of more than one kind and one or more of 90 to 60 at% of one or more kinds of iron group elements such as Fe, Co and Ni. In order to improve corrosion resistance, a small amount of elements such as Cr, Mn, Cu, Ti, Al, Si, Pt, and In may be added thereto.
[0034]
In the case of a heavy rare earth-iron group amorphous alloy, the saturation magnetization can be controlled by the composition ratio of the rare earth element and the iron group element. The Curie temperature can also be controlled by the composition ratio. In order to control the Curie temperature independently of the saturation magnetization, a material in which a part of Fe is replaced with Co is used as the iron group element, and the amount of substitution is set. A method of controlling can be used more preferably. That is, by replacing Fe 1 at% with Co, an increase in Curie temperature of about 6 ° C. can be expected. Therefore, the amount of Co added is adjusted to achieve a desired Curie temperature using this relationship. In addition, the Curie temperature can be lowered by adding a small amount of a nonmagnetic element such as Cr or Ti. Alternatively, the Curie temperature can be controlled by adjusting the composition ratio using two or more kinds of rare earth elements.
[0035]
In addition, a material such as garnet, a platinum group-iron group periodic structure film, or a platinum group-iron group alloy can also be used.
[0036]
As the first magnetic layer, for example, a rare earth-iron group amorphous alloy having small perpendicular magnetic anisotropy such as GdCo, GdFeCo, GdFe, NdGdFeCo, or a bubble memory material such as garnet is desirable.
[0037]
Examples of the third magnetic layer include perpendicular magnetic anisotropy such as rare earth-iron group amorphous alloys such as TbFeCo, DyFeCo, and TbDyFeCo, and platinum group-iron group periodic structure films such as Pt / Co and Pd / Co. It is desirable that it has a large property and can stably maintain a magnetized state.
[0038]
Data signals are recorded on the magneto-optical recording medium by moving the medium and modulating the external magnetic field while irradiating the laser beam with a power such that the third magnetic layer reaches the Curie temperature or higher. This is done by modulating the laser power while applying a directional magnetic field. In the latter case, if the intensity of the laser beam is adjusted so that only a predetermined region in the light spot is close to the Curie temperature of the third magnetic layer, a recording magnetic domain smaller than the diameter of the light spot can be formed. A signal with a period less than the diffraction limit can be recorded.
[0039]
Furthermore, FIG. 6 shows the configuration of a medium provided with a fourth magnetic layer. In this embodiment, a dielectric layer 65, a first magnetic layer 61, a fourth magnetic layer 64, a second magnetic layer 62, a third magnetic layer 63, and a dielectric layer 64 are sequentially formed on the transparent substrate 66. Are stacked. The material and manufacturing method of each layer are the same as those described with reference to FIG.
[0040]
【Example】
EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and reference examples, but the present invention is not limited to the following examples unless it exceeds the gist.
[0041]
First, reference examples and examples of magneto-optical recording media having first to third magnetic layers as shown in FIG.
[0042]
<Reference Example 1>
After attaching B-doped Si and Gd, Dy, Tb, Fe, and Co targets to a DC magnetron sputtering apparatus and fixing a polycarbonate substrate with a tracking guide groove formed on the substrate holder, 1 × 10 ^-Five The chamber was evacuated with a cryopump until a high vacuum of Pa or lower was reached. While evacuating, Ar gas was introduced into the chamber until the pressure reached 0.3 Pa, and an SiN layer as an interference layer was formed to 800 Å while rotating the substrate. Subsequently, a GdCo layer as a first magnetic layer was formed in a thickness of 300 Å, a DyFe layer as a second magnetic layer in a thickness of 100 Å, and a TbFeCo layer as a third magnetic layer in a thickness of 400 Å in this order. Finally, an SiN layer was formed as a protective layer in a thickness of 800 Å. In addition to Ar gas, N in the SiN layer deposition ₂ A gas was introduced and a film was formed by direct current reactive sputtering. Each magnetic layer was formed by applying direct current power to each target of Gd, Dy, Tb, Fe, and Co.
[0043]
The composition of each magnetic layer is adjusted so that all are close to the compensation composition, and the Curie temperature is about 300 ° C. or higher for the first magnetic layer, 70 ° C. for the second magnetic layer, and about 200 ° C. for the third magnetic layer. It set so that it might become.
[0044]
In this medium, as shown in a sectional shape in FIG. 7A, a dielectric layer 72, a magnetic layer 73, and a dielectric layer 74 are laminated on a substrate 71, and a guide groove of the substrate 71 has a depth of 1000 angstroms. It is formed in a rectangle. For this reason, the magnetic layer 72 laminated on the land 76 is substantially separated at the guide groove 75 portion. Actually, some film is deposited also on the stepped portion and the magnetic layer is connected, but since the film thickness is very thin compared with other portions, the coupling at the stepped portion can be ignored. In the present invention, such a state is also included that each information track is magnetically separated from each other. When the reversed magnetic domain is formed on the land 76 to the full width, a domain wall 77 that is not closed is formed at the boundary of the magnetic domain on the land 76 as shown in FIG. Even if such a domain wall 77 is moved in the track direction, the domain wall 77 on the side of the track is not generated or disappeared, so that it can be easily moved.
[0045]
The recording / reproducing characteristics of the magneto-optical recording medium thus obtained were measured.
[0046]
In the recording / reproducing apparatus used for the measurement, as shown in FIG. 8, a heating laser is added to the optical system of a general magneto-optical disk recording / reproducing apparatus. Reference numeral 81 denotes a laser light source for recording / reproduction, which has a wavelength of 780 nm and is arranged so that P-polarization is incident on the recording medium. Reference numeral 82 denotes a heating laser light source, which has a wavelength of 1.3 m and is arranged so that P-polarization is incident on the recording medium. Reference numeral 83 denotes a dichroic mirror designed to transmit 100% of 780 nm light and reflect 100% of 1.3 m light. Reference numeral 84 denotes a deflecting beam splitter, which is designed to transmit 780 nm light and 1.3 m light, each transmitting P deflection of 70 to 80% and reflecting S deflection 100%. The beam diameter of 1.3 m light is made smaller than the aperture diameter of the objective lens 85, and the NA is made smaller than that of 780 nm light collected through the entire aperture. 87 is provided to prevent 1.3 m light from leaking into the signal detection system, and is designed to transmit 100% of 780 nm light and reflect 100% of 1.3 m light. It is a mirror.
[0047]
With this optical system, a recording / reproducing spot 91 and a heating spot 92 are formed on the land 95 between the guide grooves 94 on the recording surface of the recording medium 86 as shown in FIG. Can be imaged. The heating spot 92 has a longer wavelength and a smaller NA, and therefore has a larger diameter than the recording / reproducing spot 91. As a result, a desired temperature gradient as shown in FIG. 9B can be easily formed in the area of the recording / reproducing spot 91 on the recording surface of the moving medium. Where temperature T _s The isotherm 96 is also illustrated. Recording / reproduction was performed by driving the medium at a linear velocity of 5 m / sec.
[0048]
First, by modulating the magnetic field at 150 Oe while irradiating the recording / reproducing laser with DC at 8 mW, the upward magnetization corresponding to the modulation of the magnetic field can be obtained in the cooling process after heating to the Curie temperature or higher of the third magnetic layer. A repetitive pattern with downward magnetization was formed. At this time, it is also possible to reduce the recording power of the recording / reproducing laser by irradiating the heating laser together.
[0049]
The modulation frequency of the recording magnetic field was varied from 1 to 10 MHz, and a mark length pattern in the range of 2.5 to 0.25 m was recorded.
[0050]
The power of the recording / reproducing laser during reproduction was 1 mW, and the C / N was measured for each mark length pattern while simultaneously irradiating the heating laser with a power of 20 mW. The temperature distribution on the medium surface at this time is as shown in FIG.
[0051]
The measurement result is shown by a graph line a in FIG. For comparison, the measurement result by the conventional super-resolution reproduction method described in Japanese Patent Laid-Open No. 3-93058 in the figure is shown as a graph line b, and the measurement result by the normal reproduction method in which the super-resolution phenomenon does not occur is a graph. Shown as line c.
[0052]
According to this reproduction method, even if the mark length is shortened, the reversal of the total magnetization in the reproduction spot is detected, so that not only the signal having a period less than the diffraction limit of light can be reproduced, but also C / N Almost no mark length dependency.
[0053]
In the medium of this reference example, the manner in which the domain wall of the first magnetic layer moves due to the temperature gradient was confirmed by direct observation with a polarizing microscope as described below.
[0054]
First, a sample having the same configuration as that of Reference Example 1 and having the magnetic layers laminated in the reverse order was manufactured. A magnetic domain pattern was formed on this sample by the same recording method as in Reference Example 1. This was observed with a polarizing microscope from the film surface side, that is, from the first magnetic layer side.
[0055]
Next, this sample was irradiated with a condensing laser for heating to form a temperature distribution almost the same as in Reference Example 1 within the field of view of the polarizing microscope.
[0056]
In this state, a magnetic field of about 500 Oe was applied to the sample. As a result, only a circular region corresponding to the temperature distribution was observed to be oriented in the direction of the external magnetic field. This means that the exchange coupling between the first magnetic layer and the third magnetic layer is broken in this region.
[0057]
Next, the application of the magnetic field was stopped, and the sample was slowly moved in the track direction. Then, each time the boundary between the magnetic domains formed on the track enters the above-described circular coupled cutting region, it has been observed that the magnetic domain that has moved expands toward the center of the circular region.
[0058]
When the irradiation of the heating laser was stopped, it was observed that the magnetic domain pattern stored in the third magnetic layer was transferred to the first magnetic layer.
[0059]
From the above, it was confirmed that the domain wall of the first magnetic layer moves to the high temperature side due to the temperature gradient in the region where the coupling with the third magnetic layer is broken.
[0060]
<Reference Example 2>
A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner using the same film forming machine and film forming method as in Reference Example 1. However, in this reference example, the following three points were changed.
[0061]
First, accelerated Ar ion irradiation treatment was applied to the substrate surface before film formation, and second, Ar ion accelerated irradiation treatment was applied to the film surface after the SiN layer as the interference layer was formed. That is. By these treatments, the surface state was smoothed. Thirdly, the thickness of the first magnetic layer is changed to 2000 angstroms. These changes contribute independently to the improvement of the domain wall mobility of the first magnetic layer.
[0062]
When the recording / reproducing characteristics of this medium were measured by the same method as in Reference Example 1, the same good results as in Reference Example 1 were obtained. Further, even when the linear velocity of the medium during reproduction was increased to 20 m / sec and reproduction was performed, the reproduction characteristics did not deteriorate.
[0063]
<Example 1>
A magneto-optical recording medium was manufactured by forming a thin film on a polycarbonate substrate in the same manner using the same film forming apparatus and film forming method as in Reference Example 1.
[0064]
However, in this embodiment, a substrate in which prepits are formed and the cross-sectional shape of the guide groove is U-shaped is used as the substrate. For this reason, the laminated magnetic layers are not divided in shape at the guide groove portions.
[0065]
The medium was irradiated with high-power laser on the guide groove portion of this medium, and the magnetic layer in the guide groove portion was annealed on the entire surface. As a result, the magnetic layer in the guide groove portion was altered to become an in-plane film, and the coupling between the magnetic layers of the tracks adjacent to each other was broken through the guide groove. When the recording / reproducing characteristics of this medium were measured by the same method as in Reference Example 1, the same good results as in Reference Example 1 were obtained.
[0066]
Further, when the recording / reproducing characteristics of the above medium were measured by the same method as in Reference Example 1 without performing the above-described annealing treatment, noise increased compared to the result of Reference Example 1, but the light diffraction limit or less was reached. It was possible to reproduce a signal with a period of. In this medium, since there are magnetic domains surrounded by closed magnetic walls, the operation becomes unstable and noise increases when the magnetic walls are moved in the direction of expanding the magnetic domains.
[0067]
As another method for breaking the coupling between the magnetic layers of adjacent tracks, patterning by an etching process may be performed.
[0068]
<Comparative Example 1>
Using the medium of Reference Example 1, the recording / reproducing characteristics were measured by a normal magneto-optical disk recording / reproducing apparatus to which no heating laser was added.
[0069]
Except that the laser for heating was not irradiated, the reproduction characteristics were examined in the same manner as in Reference Example 1, and good C / N was obtained by increasing the reproduction power to about 3 mW. However, compared with the result of Reference Example 1, the C / N was about 5 dB lower at each mark length. This is because the temperature of the medium does not increase at the front part of the reproduction spot, so that the domain wall moves from the middle of the reproduction spot, and the entire spot cannot be used effectively as in Reference Example 1.
[0070]
Next, reference examples and examples of magneto-optical recording media having the first to fourth magnetic layers as shown in FIG. 6 will be described below.
[0071]
<Reference Example 3>
After attaching B-doped Si and Gd, Tb, Fe, Co, and Cr targets to a DC magnetron sputtering apparatus and fixing the polycarbonate substrate on which a tracking guide groove is formed to the substrate holder, 1 × 10 ^-Five The chamber was evacuated with a cryopump until a high vacuum of Pa or lower was reached.
[0072]
While evacuating, Ar gas was introduced into the chamber until the pressure reached 0.3 Pa, and an SiN layer as an interference layer was formed to 800 Å while rotating the substrate. Subsequently, the GdCoCr layer is 300 angstroms as the first magnetic layer, the GdFeCr layer is 300 angstroms as the fourth magnetic layer, the TbFeCr layer is 100 angstroms as the second magnetic layer, and the TbFeCo layer is 400 angstroms as the third magnetic layer. A film was formed. Finally, an SiN layer was formed as a protective layer in a thickness of 800 Å. In addition to Ar gas, N in the SiN layer deposition ₂ A gas was introduced and a film was formed by direct current reactive sputtering. Each magnetic layer was formed by applying direct current power to each target of Gd, Tb, Fe, Co, and Cr.
[0073]
The composition of each magnetic layer is adjusted so as to be close to the compensation composition, and the Curie temperature is 300 ° C. or higher for the first magnetic layer, 170 ° C. for the fourth magnetic layer, 70 ° C. for the second magnetic layer, It set so that the 3rd magnetic layer might be about 200 degreeC. Similar to Reference Example 1, this medium has a cross-sectional shape as shown in FIG.
[0074]
The recording / reproduction characteristics of the magneto-optical recording medium thus obtained were measured in the same manner as in Reference Example 1. However, the DC irradiation laser power during recording was 10 mW, and the heating laser power during reproduction was 25 mW. As for this measurement result, the good result of the graph line a of FIG.
[0075]
Furthermore, even when the linear velocity of the medium during reproduction was increased to 20 m / sec and reproduction was performed, the reproduction characteristics did not deteriorate.
[0076]
The manner in which the domain wall of the first magnetic layer moves due to the temperature gradient was confirmed by direct observation with a polarizing microscope, as in Reference Example 1.
[0077]
<Example 2>
A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate substrate in the same manner using the same film forming apparatus and film forming method as in Reference Example 3.
[0078]
However, in this embodiment, a substrate in which prepits are formed and the cross-sectional shape of the guide groove is U-shaped is used as the substrate. For this reason, the laminated magnetic layers are not divided in shape at the guide groove portions.
[0079]
The other construction of the magnetic layer was the same as that of Reference Example 3, except that the composition ratio of the fourth magnetic layer was changed as described below.
[0080]
The fourth magnetic layer includes a sample (1) in which the composition ratio of Gd in GdFeCr is adjusted to be a composition in which the iron group element sublattice magnetization is dominant at room temperature, the rare earth element sublattice magnetization is dominant at room temperature, and the Curie temperature or lower. A sample (2) having a composition with a compensation temperature at a temperature of 2 and a sample (3) having a composition with a rare earth element sublattice magnetization dominant at room temperature and no compensation temperature at a temperature equal to or lower than the Curie temperature were prepared. The Curie temperature of each sample was adjusted to 170 ° C. by adjusting the amount of Cr added.
[0081]
In these samples, the guide groove portion was irradiated with a high-power laser, and the magnetic layer in the guide groove portion was annealed over the entire surface. As a result, the magnetic layer in the guide groove portion was magnetically altered, and the coupling between the magnetic layers of the tracks adjacent to each other via the guide groove was broken.
[0082]
Next, when the recording / reproducing characteristics were measured by the same method as in Reference Example 3, the same good results as in Reference Example 2 were obtained for each sample at a linear velocity of 5 m / sec.
[0083]
However, when the linear velocity was increased to 30 m / sec and playback was performed, in the sample (1), the C / N decreased by about 5 dB. On the other hand, in the sample (2), almost no decrease in C / N was observed, and in the sample (3), only a decrease of about 2 dB was observed.
[0084]
This is because the composition of the rare earth element sublattice magnetization dominant at room temperature, especially the composition having the compensation temperature below the Curie temperature, has a greater temperature dependence of the domain wall energy in the vicinity of the Curie temperature. This is probably because a larger force can be applied to the domain wall.
[0085]
The present invention is not limited to the examples given above. As another possible example, a method of adjusting the temperature distribution on the medium by another means while keeping the optical head as the conventional one can be considered. For example, it is conceivable to use the core of the flying head used for magnetic field modulation recording as a heat source, or to arrange another suitable heating element near the laser irradiation area for reproducing the medium. However, in this case, care must be taken so that the positional relationship between the temperature position at which the domain wall starts moving and the reproduction spot do not fluctuate at a frequency close to the frequency of the reproduction signal.
[0086]
【The invention's effect】
As described above in detail, according to the present invention, a signal having a period equal to or less than the diffraction limit of light can be reproduced at high speed without lowering the reproduction signal amplitude, and the recording density and transfer speed can be greatly improved. A magneto-optical recording medium capable of downsizing the apparatus can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a concept of a reproducing method when a magneto-optical recording medium having first to third magnetic layers manufactured according to the present invention is used. (A) shows the cross section of the medium in the reproduction state, and schematically shows the spin orientation state of each magnetic layer. (B) shows the temperature distribution on the medium at the position shown in (a). (C) schematically shows the distribution of the domain wall energy density at the same position and the distribution of the force acting on the domain wall.
FIG. 2 shows a time required for the domain wall to pass under the spot and a time t required for the medium to move a distance corresponding to the shortest recording mark length. _min It is a graph which shows the relationship.
FIG. 3 is a schematic diagram comparing a reproduction method applied to the present invention with a normal conventional method.
FIG. 4 is a diagram schematically showing a concept of a reproducing method when a magneto-optical recording medium having first to fourth magnetic layers is used.
FIG. 5 is a schematic cross-sectional view showing an embodiment of a layer structure of a magneto-optical recording medium manufactured according to the present invention.
FIG. 6 is a schematic cross-sectional view showing an embodiment of a layer structure of a magneto-optical recording medium manufactured according to the present invention.
FIG. 7 is a diagram showing a cross-sectional shape of a magneto-optical recording medium in Examples and Reference Examples.
FIG. 8 is a schematic diagram showing a recording / reproducing apparatus used in Examples and Reference Examples.
FIG. 9 is a schematic diagram showing a reproduction state in an example and a reference example.
FIG. 10 is a graph showing C / N obtained in a reference example.
[Explanation of symbols]
11 First magnetic layer
12 Second magnetic layer
13 Third magnetic layer
14 Direction of atomic spin
15 domain wall
16 Reproduction-like light beam spot
17 Direction of domain wall movement
18 Direction of media movement

Claims (2)

In a method of manufacturing a magneto-optical recording medium in which information on the recording medium is reproduced by moving a domain wall of the recording magnetic domain by a force generated due to a gradient of a temperature distribution formed on the recording medium. In addition, at least a first magnetic layer that contributes to information reproduction and in which a domain wall moves, a third magnetic layer that retains a recording magnetic domain according to information, the first magnetic layer, and the third magnetic layer A step of forming a first magnetic layer, a second magnetic layer, and a third magnetic layer in this order, and a second magnetic layer disposed between the second magnetic layer and having a Curie temperature lower than the two layers. And an annealing process for breaking magnetic coupling between magnetic layers of adjacent information tracks by irradiating a high-power laser beam between the information tracks and altering the magnetic layer existing between the information tracks. Manufacturing method of magneto-optical recording medium After forming the first magnetic layer and before forming the second magnetic layer, a fourth Curie temperature lower than the first magnetic layer is higher than the Curie temperature of the second magnetic layer. 2. The method of manufacturing a magneto-optical recording medium according to claim 1, wherein a magnetic layer is formed.

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