JP4507153B2 - Magnetic recording medium, manufacturing method thereof, and magnetic recording / reproducing apparatus - Google Patents

Description

非磁性基板上に配向制御層としてＲｕ膜を２０ｎｍの厚さで形成し、その上に垂直磁気記録層として、表１記載の組成の磁性材料からなる膜を２０ｎｍの厚さで形成した場合の磁気特性、記録再生特性を表１に示す。
【００１６】
表１に示す保磁力は、垂直方向の保磁力を意味しており、値が大きいほうが記録再生時の分解能特性が良好であり、磁化の熱的な安定性も増す。また、比（Ｍｒ／Ｍｓ）の値は磁性層の磁化の熱的安定性を表す指標である。さらに−Ｈｎは、磁性層の磁化の熱的な安定性を表す指標であり、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）は磁性層を構成するＣｏ合金結晶の磁化容易軸が基板垂直方向にどの程度そろっているかを示す指標である。
【００１７】
また、ｖＩｓｂは活性化磁気モーメントを表しており、記録再生時におけるノイズの大きさと密接な関係があり、この値が小さいほうがノイズも小さい。ここで、活性化磁気モーメント（ｖＩｓｂ）は、ＶＳＭを用いた垂直磁性層の垂直方向の保磁力（Ｈｃ-ｖ）の時間依存特性測定データを基にして次のように算出したものである。なお測定時の温度条件は室温とすることができる。
【００１８】
（Ｉ）下記のシャーロック（Ｓｈａｒｒｏｃｋ）の式（例えば、Ｊ．Ａｐｐｌ．Ｐｈｙｓ．６２（７）、ｐ２９１８。）に時間依存特性測定データを代入して（Ｋｕ×Ｖ）／（ｋ×Ｔ）を求める。
【００１９】
【数１】

【００２０】
Ａ＝１×１０⁹、ｎ＝０．５、 ｋ：ボルツマン定数、Ｈｃ０：理論上の最大保磁力
【００２１】
具体的には以下のように求めることができる。
（１）磁化曲線を測定す際の１ループあたりの時間ｔを何点か変化させ（例えば、３０秒、６０秒、１８０秒、３００秒、６００秒）、それぞれの磁化曲線から保磁力（Ｈｃ）を求める。磁化曲線の測定器は、一般に用いられるＶＳＭまたはＫｅｒｒ効果による磁気特性測定装置を用いることができる。
【００２２】
（２）ｍ通りに変化させたときにｍ通りの（測定時間、保磁力）のデータの組み合わせが得られる。
【００２３】
（３）これらのデータを、｛ｌｎ（Ａ×ｔ／０．６３５）｝^0.5をＸ軸、ＨｃをＹ軸としたグラフ上にプロットする。
【００２４】
（４）プロットしたデータから近似直線を求める。
【００２５】
（５）近似直線の傾きからＨｃ０×（ｋ×Ｔ／Ｋｕ×Ｖ）^0.5を、Ｙ軸切片からＨｃ０を読み取る。
【００２６】
（６）これから（Ｋｕ×Ｖ／ｋ×Ｔ）を求める。
【００２７】
（ＩＩ）次に、求めた（Ｋｕ×Ｖ／ｋ×Ｔ）を下記の式に代入して活性化磁気モーメント（ｖＩｓｂ）を求める。
【００２８】
【数２】

【００２９】
表１の試料１〜５は、Ｃｒの含有量を固定しＰｔ含有量を増加させている。その結果、保磁力（Ｈｃ）、（Ｍｒ／Ｍｓ）比は増加している。−Ｈｎは増加しているが、磁性層の垂直磁気異方性を表す（Ｈｃ-ｖ）／（Ｈｃ-ｉ）に変化は見られない。むしろ、記録再生時のノイズと密接な関係をもつｖＩｓｂの値が増加している。
【００３０】
垂直磁性層の磁気特性改善のためにＰｔ含有量を増加させる方法を用いた場合は、分解能、熱的な安定性を向上させることができるが、反面、磁性層の結晶配向性を改善することはできず、磁性粒子間の相互作用の増加によるノイズの増加といったことが生じることを意味している。
【００３１】
一方、表１の試料６〜１０に示すように、Ｐｔの代わりにＮｄを添加し、その添加量を増加した場合、Ｐｔと同様にＨｃ、Ｍｒ／Ｍｓ比は増加している。また−Ｈｎを増加させることができることがわかる。（Ｈｃ-ｖ）／（Ｈｃ-ｉ）の値も大きくなっているので磁性層の結晶配向性が改善されていることが推定され、その結果Ｈｃ、Ｍｒ／Ｍｓ、−Ｈｎが向上していると考えられる。ここで注目する点は、これら特性の改善を得た状態でｖＩｓｂの値の増加を抑えることができていることである。Ｐｔの存在下においてＮｄを磁性材料に添加する本発明により、記録再生時のノイズを増加させることなく、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）を改善し、Ｈｃ、Ｍｒ／Ｍｓ、−Ｈｎのような磁気特性を向上させることがわかる。
【００３２】
また、Ｎｄを８ａｔ％を超えて添加すると、磁気特性が低下している。一方、ＣｏＣｒのみからなる磁性材料やＰｔ量が１０ａｔ％未満の磁性材料にＮｄを添加しても磁気特性が低下している。基になる磁性材料の磁気異方性定数（Ｋｕ）が小さいため、磁気特性の改善効果が少ないからと考えられる。このことから、より効果的にＮｄの改善効果を得るには、１０ａｔ％以上のＰｔの存在下でＮｄを添加することが好ましいことがわかる。
【００３３】
Ｎｄを添加することで何故磁気特性が向上するのかは、完全に明らかではないが、次のように推測することができる。Ｃｏを主成分とする磁性材料にＮｄを添加すると、Ｃｏの一部とＮｄにより、ＣｏとＮｄの金属化合物（ＮｄＣｏ５やＮｄ２Ｃｏ１７等）が形成されることがあると考える。これらＮｄとＣｏの金属化合物は希土類−コバルト磁石の原料と同じ組成であり、その組成の合金は結晶磁気異方性や磁気異方性定数（Ｋｕ）の値が大きいことが知られている。この化合物が形成されることにより磁性層全体の磁気異方性定数（Ｋｕ）が向上し、また、これらの結晶の磁化容易軸を基板に対して垂直方向に向けることで、垂直磁気異方性（Ｈｃ-ｖ／Ｈｃ-ｉ）の値が大きくなる。その結果、垂直磁性層全体の保磁力（Ｈｃ）、Ｍｒ／Ｍｓ比、−Ｈｎに代表される磁気特性を向上させると考えられる。さらに、単にＰｔの添加量を増加させた場合と異なり、Ｎｄの添加はＣｒ偏析を阻害してしまうことが無いため、磁性粒子の肥大化や磁性粒子間相互作用を大きくする作用がなく、記録再生時におけるノイズを増加させないと考えられる。
【００３４】
ここで、Ｐｔを存在させていないと磁性粒子内部にある程度の磁気異方性を有しない状態になるので、磁化反転において反磁界の影響が大きく、結果として、高密度記録に必要な保磁力やＭｒ／Ｍｓ、−Ｈｎといった磁気特性を得ることが難しくなると考えられる。
【００３５】
本実施形態の磁気記録媒体にあっては、垂直磁性層５を、Ｃｏを主成分としてすくなくともＣｒ、Ｐｔを含む材料からなるものとし、さらにＮｄを添加した磁性材料より形成して、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓを０．８５以上として、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントを０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕであるとしている。
【００３６】
さらに、配向制御層と磁性層との間にｈｃｐ構造を有する中間膜を設けることにより、残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）の比Ｍｒ／Ｍｓ、保磁力（Hc-ｖ）、垂直方向の保磁力（Ｈｃ-ｖ）と面内方向の保磁力（Ｈｃ-ｉ）の比（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、逆磁区核形成磁界（−Ｈｎ）向上させている。
【００３７】
その結果、記録再生時の分解能の向上や熱揺らぎ耐性を大きく改善され、また活性化磁気モーメント（ｖＩｓｂ）の増加が抑えられているので記録再生時のノイズを低くし高密度記録に必要な信号／ノイズ比（Ｓ／Ｎ）が確保できているので、本発明の磁気記録媒体は記録再生特性が改善された磁気記録媒体となる。
【００３８】
なお、熱揺らぎとは、記録ビットが不安定となり記録したデータの熱消失が生じる現象をいい、磁気記録媒体装置においては、記録したデータの再生再生出力の経時的な減衰として現れる。
【００３９】
【発明の実施の形態】
図１は、本発明の磁気記録媒体の第１の実施形態を示すもので、ここに示す磁気記録媒体は、非磁性基板１上に、軟磁性下地層２と、配向制御層３と、中間層４と、垂直磁性層５と、保護層６と潤滑層７とが順次形成されて構成されている。
【００４０】
非磁性基板１としては、アルミニウム、アルミニウム合金等の金属材料からなる金属基板を用いてもよいし、ガラス、セラミック、シリコン、シリコンカーバイド、カーボンなどの非金属材料からなる非金属基板を用いてもよい。
【００４１】
ガラス基板としては、アモルファスガラス、結晶化ガラスがあり、アモルファスガラスとしては汎用のソーダライムガラス、アルミノケートガラス、アルミノシリケートガラスを使用できる。また、結晶化ガラスとしては、リチウム系結晶化ガラスを用いることができる。セラミック基板としては、汎用の酸化アルミニウム、窒化アルミニウム、窒化珪素などを主成分とする焼結体や、これらの繊維強化物などが使用可能である。
【００４２】
非磁性基板１としては、上記金属基板、非金属基板の表面にメッキ法やスパッタ法を用いてＮｉＰ層が形成されたものを用いることもできる。
【００４３】
本発明では、配向制御層の下に軟磁性層２を設けるのが好ましい。軟磁性下地層２は、ヘッドから出てくる磁束の基板に対する垂直方向成分を大きくすること、および情報が記録される垂直磁性層５の磁化の方向をより強固に基板１と垂直な方向に固定することができるからである。この作用は特に、記録再生用の磁気ヘッドとして垂直記録用の単磁極ヘッドを用いる場合に、より顕著なものとなる。
【００４４】
上記軟磁性下地層２は、軟磁性材料からなるもので、この材料としては、Ｆｅ、Ｎｉ、Ｃｏを含む材料を用いることができる。この材料としては、ＦｅＣｏ系合金（ＦｅＣｏ、ＦｅＣｏＶ）、ＦｅＮｉ系合金（ＦｅＮｉ、ＦｅＮｉＭｏ、ＦｅＮｉＣｒ、ＦｅＮｉＳｉ）、ＦｅＡｌ系合金（ＦｅＡｌ、ＦｅＡｌＳｉ、ＦｅＡｌＳｉＣｒ、ＦｅＡｌＳｉＴｉＲｕ、ＦｅＡｌＯ）、ＦｅＣｒ系合金（ＦｅＣｒ、ＦｅＣｒＴｉ、ＦｅＣｒＣｕ）、ＦｅＴａ系合金（ＦｅＴａ、ＦｅＴａＣ、ＦｅＴａＮ）、ＦｅＭｇ系合金（ＦｅＭｇＯ）、ＦｅＺｒ系合金（ＦｅＺｒＮ）、ＦｅＣ系合金、ＦｅＮ系合金、ＦｅＳｉ系合金、ＦｅＰ系合金、ＦｅＮｂ系合金、ＦｅＨｆ系合金、ＦｅＢ系合金を挙げることができる。
【００４５】
またＦｅを６０ａｔ％以上含有するＦｅＡｌＯ、ＦｅＭｇＯ、ＦｅＴａＮ、ＦｅＺｒＮ等の微結晶構造を有する材料、あるいは微細な結晶粒子がマトリクス中に分散されたグラニュラー構造を有する材料を用いてもよい。
【００４６】
軟磁性下地層２の材料としては、上記のほか、Ｃｏを８０ａｔ％以上含有し、Ｚｒ、Ｎｂ、Ｔａ、Ｃｒ、Ｍｏ等のうち少なくとも１種を含有し、アモルファス構造を有するＣｏ合金を用いることができる。この材料としては、ＣｏＺｒ、ＣｏＺｒＮｂ、ＣｏＺｒＴａ、ＣｏＺｒＣｒ、ＣｏＺｒＭｏ系合金などを好適なものとして挙げることができる。
【００４７】
軟磁性下地層２の保磁力Ｈｃは２００［Ｏｅ］以下（好ましくは５０［Ｏｅ］以下）とするのが好ましい。この保磁力Ｈｃが上記範囲を超えると、軟磁気特性が不十分となり、再生信号波形がいわゆる矩形波から歪みをもった波形になるため好ましくない。
【００４８】
軟磁性下地層２の飽和磁束密度Ｂｓは、０．６Ｔ以上（好ましくは１Ｔ以上）とするのが好ましい。このＢｓが上記範囲未満であると、再生信号波形がいわゆる矩形波から歪みをもった波形になるため好ましくない。
【００４９】
軟磁性層の膜厚は、５０〜４００ｎｍであるのが好ましい。この範囲であると再生信号波形において歪のない波形が得られるからである。
【００５０】
また、軟磁性下地層２の飽和磁束密度Ｂｓ（Ｔ）と軟磁性下地層２の層厚ｔ（ｎｍ）との積Ｂｓ・ｔ（Ｔ・ｎｍ）が２０（Ｔ・ｎｍ）以上（好ましくは４０（Ｔ・ｎｍ）以上）であること好ましい。このＢｓ・ｔが上記範囲未満であると、再生信号波形が歪みをもつようになったり、ＯＷ特性が悪化するため好ましくない。
【００５１】
軟磁性下地層２の最表面（配向制御層３側の面）は、軟磁性下地層２を構成する材料が部分的、あるいは完全に酸化されて構成されていることが好ましい。つまり、軟磁性下地層２の表面（配向制御層３側の面）およびその近傍に、軟磁性下地層２を構成する材料が部分的に酸化されるか、もしくは前記材料の酸化物を形成して配されていることが好ましい。これにより、軟磁性下地層２の表面の磁気的な揺らぎを抑えることができるので、この磁気的な揺らぎに起因するノイズの低減して、磁気記録媒体の記録再生特性を改善することができる。また、軟磁性下地層２上に形成される配向制御層３の結晶粒の微細化して、記録再生特性を改善することができる。
【００５２】
この軟磁性下地層２の表面の酸化された部分は、例えば軟磁性下地層２を形成した後、酸素を含む雰囲気に曝す方法や、軟磁性下地層２の表面に近い部分を成膜する際のプロセス中に酸素を導入する方法により形成することができる。具体的には、軟磁性下地層２の表面を酸素に曝す場合には、酸素単体、あるいは酸素をアルゴンや窒素などのガスで希釈したガス雰囲気中に０．３〜２０秒程度保持しておけばよい。また、大気中に曝すこともできる。特に酸素をアルゴンや窒素などのガスで希釈したガスを用いる場合には、軟磁性下地層２表面の酸化の度合いの調節が容易になるので、安定した製造を行うことができる。また、軟磁性下地層２の成膜用のガスに酸素を導入する場合には、例えば成膜法としてスパッタ法を用いるならば、成膜時間の１部のみに酸素を導入したプロセスガスを用いてスパッタを行えばよい。このプロセスガスとしては、例えばアルゴンに酸素を体積率で０．０５％〜５０％（好ましくは０．１〜２０％）程度混合したガスが好適に用いられる。
【００５３】
配向制御層３は、直上に設けられた中間層４および垂直磁性層５の配向性や粒径を制御するものである。
【００５４】
この材料としては、特に限定されるものではないが、ｈｃｐ構造、ｆｃｃ構造、アモルファス構造を有するものが好ましい。特に、Ｒｕ系合金、Ｎｉ系合金、Ｃｏ系合金が特に好ましい。
【００５５】
本実施形態の磁気記録媒体では、配向制御層３の厚さを０．５〜４０ｎｍ（好ましくは１〜２０ｎｍ）とするのが好ましい。配向制御層３の厚さが０．５〜４０ｎｍ（好ましくは１〜２０ｎｍ）の範囲であるとき、垂直磁性層５の垂直配向性が特に高くなり、かつ記録時における磁気ヘッドと軟磁性下地層２との距離を小さくすることができるので、再生信号の分解能を低下させることなく記録再生特性を高めることができる。この厚さが上記範囲未満であると、垂直磁性層５における垂直配向性が低下し、記録再生特性および熱揺らぎ耐性が劣化する。また、この厚さが上記範囲を超えると、垂直磁性層５の磁性粒子径が大きくなり、ノイズ特性が劣化するおそれがあるため好ましくない。また記録時における磁気ヘッドと軟磁性下地層２との距離が大きくなるため、再生信号の分解能や再生出力の低下するため好ましくない。
【００５６】
配向制御層３の表面形状は、垂直磁性層５、保護層６の表面形状に影響を与えるため、磁気記録媒体の表面凹凸を小さくして、記録再生時における磁気ヘッド浮上高さを低くするには、配向制御層３の表面平均粗さＲａを２ｎｍ以下とするのが好ましい。この表面平均粗さＲａを２ｎｍ以下とすることによって、磁気記録媒体の表面凹凸を小さくし、記録再生時における磁気ヘッド浮上高さを十分に低くし、記録密度を高めることができる。
【００５７】
配向制御層３の成膜用のガスに酸素や窒素を導入してもよい。例えば、成膜法としてスパッタ法を用いるならば、プロセスガスとしては、アルゴンにに酸素を体積率で０．０５〜５０％（好ましくは０．１〜２０％）程度混合したガス、アルゴンに窒素を体積率で０．０１〜２０％（好ましくは０．０２〜１０％）程度混合したガスが好適に用いられる。
【００５８】
配向制御層３と垂直磁性層５との間に、中間層４が設けることができる。中間層４を設けることによって、垂直磁性層５の垂直配向性を高めることができるので、垂直磁性層５の保磁力を高め、記録再生特性および熱揺らぎ耐性をさらに向上させることができる。
【００５９】
中間層４にはｈｃｐ構造を有する材料を用いるのが好ましい。中間層４には、ＣｏＣｒ合金やＣｏＣｒＸ１合金やＣｏＸ１合金（Ｘ１：Ｐｔ、Ｔａ、Ｚｒ、Ｒｕ，Ｎｂ、Ｃｕ、Ｒｅ、Ｎｉ、Ｍｎ、Ｇｅ、Ｓｉ、Ｏ、ＮおよびＢから選ばれる１種または２種以上）を用いるのが好適である。
【００６０】
中間層４のＣｏの含有量は３０〜７０ａｔ％であることが好ましい。この範囲であれば中間層が非磁性であるからである。
【００６１】
中間層４の厚さは、垂直磁性層５における磁性粒子の粗大化による記録再生特性の悪化や、磁気ヘッドと軟磁性下地層２との距離が大きくなることによる記録分解能の低下を起こさないようにするために、２０ｎｍ以下（好ましくは１０ｎｍ以下）とするのが好ましい。
【００６２】
垂直磁性層５は、その磁化容易軸が基板に対して主に垂直方向に向いたものであり、Ｃｏを主成分とし、少なくともＣｒ、Ｐｔ、Ｎｄを含んだ材料からなる。各元素の含有量として、Ｃｒ含有量が１８〜２８ａｔ％（好ましくは１９〜２４ａｔ％）、Ｐｔ含有量が１０〜２０ａｔ％（好ましくは１３〜１８ａｔ％）であり、Ｎｄ含有量が０．５〜８ａｔ％（好ましくは１〜４ａｔ％）であることが好ましい。
【００６３】
Ｃｒの含有量が１８ａｔ％未満であると、Ｃｒ偏析により磁性粒子間に形成される粒界層の厚さが薄くななるために磁性粒子間の磁気的な粒子間相互作用が大きくなり、また磁性粒子自体の粒径も肥大化しやすくなる。その結果記録再生時におけるノイズが増大し、より高密度記録に適した信号／ノイズ比（Ｓ／Ｎ）が得られなくなる。
【００６４】
また、Ｃｒ含有量が２８ａｔ％を超えると、Ｃｒが粒界層へ偏析しきれず磁性粒子内部に残留する割合が増加する。その結果として垂直方向の保磁力、および残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）の比Ｍｒ／Ｍｓが低下しやすくなる。さらに、磁性粒子の結晶配向性が損ねられて、垂直方向の保磁力（Ｈｃ-ｖ）と面内方向の保磁力（Ｈｃ-ｉ）の比（Ｈｃ-ｖ）／（Ｈｃ-ｉ）が小さくなってしまうおそれがある。
【００６５】
Ｐｔの含有量が１０ａｔ％未満であると、垂直磁性層に必要な磁気異方性定数（Ｋｕ）が得られず、磁化が熱的に不安定となる。また、Ｐｔが２０ａｔ％を超える場合、磁性層中のＣｒ偏析を阻害するばかりでなく、磁性層中にｆｃｃ構造の層が形成されるために保磁力の低下をもたらすおそれがあるので、上記範囲が好ましい。
【００６６】
Ｎｄの含有量が０．５ａｔ％未満であると、Ｋｕの値を大きくするという効果が低下するおそれがある。また、Ｎｄを８ａｔ％を超えて含有させると逆に保磁力が低下し、結果として記録再生時におけるノイズを増大させるおそれがある。
【００６７】
Ｂ、Ｔａ、Ｃｕは、磁性層中のＣｒ偏析を促進し、磁気的な粒子間相互作用や磁性粒子径を小さし、結果として記録再生時のノイズを減少させる効果を有する。これら元素の添加量は各元素の合計で８ａｔ％以下であることが好ましい。８ａｔ％を超えて添加した場合、これら元素が磁性粒子内に残留し、その結果、垂直保磁力および残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）の比Ｍｒ／Ｍｓが低下するため好ましくない。
【００６８】
磁性材料の例としては、Ｃｏ２０Ｃｒ１４Ｐｔ２Ｎｄ（Ｃｒ含有率２０ａｔ％、Ｐｔ含有率１４ａｔ％、Ｎｄ含有率２ａｔ％）やＣｏ２２Ｃｒ１２Ｐｔ４Ｎｄ（Ｃｒ含有率２２ａｔ％、Ｐｔ含有率１２ａｔ％、Ｎｄ含有率４ａｔ％）、Ｃｏ１９Ｃｒ１４Ｐｔ１Ｂ１Ｔａ１Ｎｄ（Ｃｒ含有率１９ａｔ％、Ｐｔ含有率１４ａｔ％、Ｂ含有率１ａｔ％、Ｔａ含有率１ａｔ％、Ｎｄ含有率１ａｔ％）、Ｃｏ２２Ｃｒ１２Ｐｔ２Ｂ２Ｎｄ（Ｃｒ含有率２２ａｔ％、Ｐｔ含有率１２ａｔ％、Ｂ含有率２ａｔ％、Ｎｄ含有率２ａｔ％）の他、ＣｏＣｒＰｔＮｄ系合金、ＣｏＣｒＰｔＢＮｄ系合金、ＣｏＣｒＰｔＴａＮｄ系合金、ＣｏＣｒＰｔＣｕＮｄ系合金、ＣｏＣｒＰｔＢＣｕＮｄ系合金の材料をあげることができる。
【００６９】
垂直磁性層５は、上記の本発明の磁性材料からなる１層構造とすることもできるし、各種の磁性材料と組み合わせて積層した多層構造とすることもできる。垂直磁性層が複数の磁性層から構成される場合、そのうち少なくとも１層が上記の垂直磁性層からなることが好ましい。特に垂直磁性層の最上の層がＮｄを含有したものであることが好ましい。
【００７０】
多層構造に用いる各種の磁性材料としては上記以外に、ＣｏＣｒＰｔ系合金、ＣｏＣｒ系合金、ＣｏＣｒＰｔＢ系合金、ＣｏＣｒＰｔＣｕ系合金のほか、Ｃｏ系合金（ＣｏＣｒ、ＣｏＢ、Ｃｏ−ＳｉＯ２等）とＰｄ系合金（ＰｄＢ、Ｐｄ−ＳｉＯ２等）の積層材料やＴｂＦｅＣｏ等のアモルファス材料とＣｏＣｒＰｔＣｕ系材料とすることもできる。
【００７１】
また、多層構造とする場合、磁性層間に非磁性材料からなる中間層を形成した構成とすることもできる。非磁性材料としては、ｈｃｐ構造を有する非磁性金属材料のほか、ｂｃｃ構造やｆｃｃ構造、アモルファス構造を有する非磁性の金属材料、酸化金属材料、窒化金属材料とすることもできる。
【００７２】
垂直磁性層５の厚さは、３〜６０ｎｍ（好ましくは５〜４０ｎｍ）とするのが好ましい。垂直磁性層５の厚さが上記範囲未満であると、十分な磁束が得られず、再生出力が低下する。また、垂直磁性層５の厚さが上記範囲を超えると、垂直磁性層５内の磁性粒子の粗大化が起き、記録再生特性が低下するため好ましくない。
【００７３】
本発明の垂直磁性層５は基板に対しての残留磁化（Ｍｓ）と飽和磁化（Ｍｒ）の比Ｍｒ／Ｍｓが０．８５以上（好ましくは０．９５以上。）である。Ｍｒ／Ｍｓが０．８５未満の磁気記録媒体は、逆磁区核形成磁界が低下するので熱揺らぎ耐性に劣るため好ましくない。
【００７４】
本発明の垂直磁性層５は、活性化体積（ｖ）と飽和磁気モーメント（Ｉｓ）の積で表される活性化磁気モーメント（ｖＩｓｂ）の値が、０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕ（好ましくは０．４×１０^-15ｅｍｕ〜０．７×１０^-15ｅｍｕ。）の範囲である。ｖＩｓｂが０．３×１０^-15ｅｍｕ未満であると、磁気クラスターサイズが小さくなりすぎ、熱的に不安定になるため、容易に熱減磁が生じ、磁気記録媒体としては好ましくない。また、ｖＩｓｂが０．８×１０^-15ｅｍｕを超える場合、記録再生時におけるノイズが大きくなりすぎ、高密度記録に必要な信号／ノイズ比（Ｓ／Ｎ）が得られなくなるため、好ましくない。
【００７５】
磁性層の垂直方向の保磁力（Ｈｃ-ｖ）は、２５００［Ｏｅ］以上とすることが好ましい。保磁力が２５００［Ｏｅ］未満の磁気記録媒体は、高記録密度には不適であり、また熱揺らぎ耐性が低下する。
【００７６】
垂直方向の保磁力（Ｈｃ-ｖ）と面内方向の保磁力（Ｈｃ-ｉ）の比で表される垂直磁気異方性（Ｈｃ-ｖ）／（Ｈｃ-ｉ）が５以上であることが好ましい。Ｈｃ-ｖ／Ｈｃ-ｉの値が５未満である場合、磁性層の結晶配向性が悪くＣｏの磁化容易軸であるＣ軸が基板垂直面に対して分散していることになるので、保磁力（Ｈｃ-ｖ）、Ｍｒ／Ｍｓ比、逆磁区核形成磁界（−Ｈｎ）の低下を招きやすい。さらに磁化が熱的に不安定であり熱減磁が生じるばかりでなく、記録再生時のノイズも増加してしまうため好ましくない。
【００７７】
垂直磁性層５の逆磁区核形成磁界（−Ｈｎ）は、０〜２０００［Ｏｅ］（より好ましくは０〜１５００［Ｏｅ］。）であることが好ましい。逆磁区核形成磁界（−Ｈｎ）が、０未満の磁気記録媒体は、熱揺らぎ耐性に劣るため好ましくない。
【００７８】
逆磁区核形成磁界（−Ｈｎ）は、図２に示すように、ＶＳＭなどにより求めたＭＨ曲線において、磁化が飽和した状態から外部磁界を減少させる過程で外部磁界が０となる点ａ、ＭＨ曲線の磁化が０である点ｂでのＭＨ曲線の接線を延長した線と飽和磁化との交点を点ｃとすると、Ｙ軸から点ｃまでの距離［Ｏｅ］で表すことができる。
なお、逆磁区核形成磁界（−Ｈｎ）は、点ｃが外部磁界が負である領域にある場合に正の値をとり（図２を参照）、逆に、点ｃが外部磁界が正である領域にある場合に負の値をとる（図３を参照）。
【００７９】
なお本明細書中で、基板に対して主に垂直方向に向いたものとは、たとえばＶＳＭで測定した、基板方向に対して垂直方向の保磁力の値が基板に対して水平方向のそれより大きいものである。
【００８０】
保護層６は垂直磁性層５の腐食を防ぐとともに、磁気ヘッドが媒体に接触したときに媒体表面の損傷を防ぐためのもので、従来公知の材料を使用でき、例えばＣ、ＳｉＯ２、ＺｒＯ２を含むものが使用可能である。
【００８１】
保護層６の厚さは、１〜１０ｎｍとするのがヘッドと媒体の距離を小さくできるので高記録密度の点から望ましい。
【００８２】
潤滑剤７には、パーフルオロポリエーテル、フッ素化アルコール、フッ素化カルボン酸などを用いるのが好ましい。
【００８３】
本発明の磁気記録媒体は、非磁性基板上に、少なくとも、直上の層の配向性を制御する配向制御層と、磁化容易軸が基板に対し主に垂直に配向した垂直磁性層と、保護層とが設けられ、垂直磁性層がＣｏを主成分とし、少なくとも、Ｃｒ、Ｐｔ、Ｎｄを含んだ材料からなり、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓが０．８５以上であり、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントが０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕであることを特徴とする磁気記録媒体であるから、磁気記録媒体の記録再生時におけるノイズを増加させることなく、記録再生特性の分解能を向上させたり磁化の熱的な安定性を高めることができる。
【００８４】
次に上記構成の磁気記録媒体を製造する方法の一例について説明する。
上記構成の磁気記録媒体を製造するには、非磁性基板１上に、軟磁性下地層２、配向制御層３、中間層４、垂直磁性層５を順次、スパッタ法、真空蒸着法、イオンプレーティング法などにより形成する。次いで保護層６を、好ましくはプラズマＣＶＤ法、イオンビーム法、スパッタ法により形成する。
【００８５】
非磁性基板１としては、アルミニウム、アルミニウム合金等の金属材料からなる金属基板を用いてもよいし、ガラス、セラミック、シリコン、シリコンカーバイド、カーボンなどの非金属材料からなる非金属基板を用いてもよい。
【００８６】
ガラス基板としては、アモルファスガラス、結晶化ガラスがあり、アモルファスガラスとしては汎用のソーダライムガラス、アルミノケートガラス、アルミノシリケートガラスを使用できる。また、結晶化ガラスとしては、リチウム系結晶化ガラスを用いることができる。セラミック基板としては、汎用の酸化アルミニウム、窒化アルミニウム、窒化珪素などを主成分とする焼結体や、これらの繊維強化物などが使用可能である。
【００８７】
非磁性基板１としては、上記金属基板、非金属基板の表面にメッキ法やスパッタ法を用いてＮｉＰ層が形成されたものを用いることもできる。
【００８８】
非磁性基板は、平均表面粗さＲａが２ｎｍ（２０Å）以下、好ましくは１ｎｍ以下であるとことがヘッドを低浮上させた高記録密度記録に適している点から望ましい。
【００８９】
また、表面の微小うねり（Ｗａ）が０．３ｎｍ以下（より好ましくは０．２５［ｎｍ］以下。）であるのがヘッドを低浮上させた高記録密度記録に適している点から好ましい。端面のチャンファー部の面取り部、側面部の少なくとも一方のいずれの表面平均粗さＲａが１０ｎｍ以下（より好ましくは９．５ｎｍ以下。）のものを用いることが磁気ヘッドの飛行安定性にとって好ましい。微少うねり（Ｗａ）は、例えば、表面荒粗さ測定装置Ｐ−１２（ＫＬＭ−Ｔｅｎｃｏｒ社製）を用い、測定範囲８０μmでの表面平均粗さとして測定することができる。
【００９０】
必要に応じて非磁性基板を洗浄して、非磁性基板を成膜装置のチャンバ内に設置する。必要に応じて基板は、例えばヒータより１００〜４００℃に加熱される。非磁性基板１上に、軟磁性下地層２と、配向制御層３と、中間層４と、垂直磁性層５を各層の材料と同じ組成の材料を原料とするスパッタターゲットを用いてＤＣ或いはＲＦマグネトロンスパッタ法により形成する。膜を形成するためのスパッタの条件は例えば次のようにする。形成に用いるチャンバ内は真空度が１０^-4〜１０^-7Ｐａとなるまで排気する。チャンバ内に基板を収容して、スパッタガスとして、たとえばＡｒガスを導入して放電させてスパッタ成膜をおこなう。このとき、供給するパワーは０．２〜２．０ｋＷとし、放電時間と供給するパワーを調節することによって、所望の膜厚を得ることができる。
【００９１】
軟磁性下地層２を放電時間と供給するパワーを調節することによって５０〜４００ｎｍの膜厚で形成するのが好ましい。
【００９２】
軟磁性下地層２を形成する際には、軟磁性材料からなるスパッタターゲットを用いるのが軟磁性下地層を容易に形成できるので好ましい。軟磁性材料としては、ＦｅＣｏ系合金（ＦｅＣｏ、ＦｅＣｏＶなど）、ＦｅＮｉ系合金（ＦｅＮｉ、ＦｅＮｉＭｏ、ＦｅＮｉＣｒ、ＦｅＮｉＳｉなど）、ＦｅＡｌ系合金（ＦｅＡｌ、ＦｅＡｌＳｉ、ＦｅＡｌＳｉＣｒ、ＦｅＡｌＳｉＴｉＲｕ、ＦｅＡｌＯなど）、ＦｅＣｒ系合金（ＦｅＣｒ、ＦｅＣｒＴｉ、ＦｅＣｒＣｕなど）、ＦｅＴａ系合金（ＦｅＴａ、ＦｅＴａＣ、ＦｅＴａＮなど）、ＦｅＭｇ系合金（ＦｅＭｇＯなど）、ＦｅＺｒ系合金（ＦｅＺｒＮなど）、ＦｅＣ系合金、ＦｅＮ系合金、ＦｅＳｉ系合金、ＦｅＰ系合金、ＦｅＮｂ系合金、ＦｅＨｆ系合金、ＦｅＢ系合金、Ｆｅを６０ａｔ％以上含有するＦｅＡｌＯ、ＦｅＭｇＯ、ＦｅＴａＮ、ＦｅＺｒＮを挙げることができる。さらに、Ｃｏを８０ａｔ％以上含有し、Ｚｒ、Ｎｂ、Ｔａ、Ｃｒ、Ｍｏ等のうち少なくとも１種を含有し、アモルファス構造を有している、ＣｏＺｒ、ＣｏＺｒＮｂ、ＣｏＺｒＴａ、ＣｏＺｒＣｒ、ＣｏＺｒＭｏ系合金を好適なものとして挙げることができる。
【００９３】
上記のターゲットは溶製法による合金ターゲットまたは焼結合金ターゲットである。
【００９４】
軟磁性下地層２を形成した後に、その表面を酸化する工程を含ませるのが好ましい。例えば軟磁性下地層２を形成した後、酸素を含む雰囲気に曝す方法や、軟磁性下地層２の表面に近い部分を成膜する際のプロセス中に酸素を導入する方法を挙げることができる。
【００９５】
軟磁性下地層２を形成後、配向制御層を、放電時間と供給するパワーを調節することによって配向制御層３を０．５〜４０ｎｍ（好ましくは１〜２０ｎｍ）の膜厚で形成する。配向制御層の形成に用いるスパッタ用ターゲットの材料としてはＲｕ系合金、Ｎｉ系合金、Ｃｏ系合金を挙げることができる。
【００９６】
配向制御層を形成した後、１５〜４０ｎｍの膜厚を有した磁性層を磁性層の材料からなるスパッタターゲットを用いて同様にスパッタ法により形成する。スパッタターゲットの材料としては、Ｃｏ２０Ｃｒ１４Ｐｔ２Ｎｄ（Ｃｒ含有率２０ａｔ％、Ｐｔ含有率１４ａｔ％、Ｎｄ含有率２ａｔ％）やＣｏ２２Ｃｒ１２Ｐｔ４Ｎｄ（Ｃｒ含有率２２ａｔ％、Ｐｔ含有率１２ａｔ％、Ｎｄ含有率４ａｔ％）、Ｃｏ１９Ｃｒ１４Ｐｔ１Ｂ１Ｔａ１Ｎｄ（Ｃｒ含有率１９ａｔ％、Ｐｔ含有率１４ａｔ％、Ｂ含有率１ａｔ％、Ｔａ含有率１ａｔ％、Ｎｄ含有率１ａｔ％）、Ｃｏ２２Ｃｒ１２Ｐｔ２Ｂ２Ｎｄ（Ｃｒ含有率２２ａｔ％、Ｐｔ含有率１２ａｔ％、Ｂ含有率２ａｔ％、Ｎｄ含有率２ａｔ％）の他、ＣｏＣｒＰｔＮｄ系合金、ＣｏＣｒＰｔＢＮｄ系合金、ＣｏＣｒＰｔＴａＮｄ系合金、ＣｏＣｒＰｔＣｕＮｄ系合金、ＣｏＣｒＰｔＢＣｕＮｄ系合金
ＣｏＣｒＰｔ系合金、ＣｏＣｒ系合金、ＣｏＣｒＰｔＢ系合金、ＣｏＣｒＰｔＣｕ系合金のほか、Ｃｏ系合金（ＣｏＣｒ、ＣｏＢ、Ｃｏ−ＳｉＯ２等）とＰｄ系合金（ＰｄＢ、Ｐｄ−ＳｉＯ２等）の積層材料やＴｂＦｅＣｏ等のアモルファス材料とＣｏＣｒＰｔＣｕ系材料を挙げることができる。
【００９７】
また、Ｃｒ、Ｐｔ、Ｎｄ以外の元素として、Ｂ、Ｔａ、Ｃｕから選ばれるいずれかの元素の内１種類以上を添加したものを用いることも好ましい。
【００９８】
Ｃｏを主成分とし、少なくともＣｒ、Ｐｔ、Ｎｄを含んだ材料からなり、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓが０．８５以上であり、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントが０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕである垂直磁性層を形成するためのスパッタの条件は例えば次のようにする。
【００９９】
Ｃｏを主成分とし、少なくともＣｒおよびＰｔさらにＮｄを含んだ材料からなるターゲットを使用し、形成に用いるチャンバ内は真空度が１０^-4〜１０^-7Ｐａとなるまで排気した状態で、チャンバ内に基板を収容して、スパッタガスとして例えばＡｒガスを導入して放電させてスパッタ成膜をおこなう。このとき、供給するパワーは０．２〜２．０ｋＷとし、放電時間と供給するパワーを調節することによって、所望の膜厚を得ることができる。
【０１００】
スパッタガスの圧力が３〜２０Ｐａ（より好ましくは５〜１５Ｐａ。）であるのが好ましい。
【０１０１】
非磁性下地層と磁性層との間に中間層を設ける場合は、ＣｏＣｒ合金（Ｃｒの含有量は２５〜４５ａｔ％）を原料としたスパッタターゲットを用いるのが好ましい。ＣｏＣｒ合金としては、ＣｏＣｒ合金やＣｏＣｒＸ１合金やＣｏＸ１合金（Ｘ１：Ｐｔ、Ｔａ、Ｚｒ、Ｒｕ，Ｎｂ、Ｃｕ、Ｒｅ、Ｎｉ、Ｍｎ、Ｇｅ、Ｓｉ、Ｏ、ＮおよびＢから選ばれる１種または２種以上）を挙げることができる。このとき、磁性層にＢを含む場合には、非磁性下地層と磁性層との境界付近において、Ｂ濃度が１ａｔ％以上の領域におけるＣｒ濃度が４０ａｔ％以下となるようなスパッタ条件で成膜するのが好ましい。
【０１０２】
磁性層を形成した後、公知の方法、例えばスパッタ法、プラズマＣＶＤ法またはそれらの組み合わせを用いて保護膜、たとえばカーボンを主成分とする保護膜を形成する。
【０１０３】
さらに、保護膜上には必要に応じパーフルオロポリエーテルのフッ素系潤滑剤をディップ法、スピンコート法などを用いて塗布し潤滑層を形成する。
【０１０４】
本発明に従って製造した磁気記録媒体は、垂直磁性層が、Ｃｏを主成分とし、少なくとも、Ｃｒ、Ｐｔ、Ｎｄを含んだ材料からなり、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓが０．８５以上であり、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントが０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕであることを特徴とする磁気記録媒体であるから、磁気記録媒体の記録再生時におけるノイズを増加させることなく、記録再生特性の分解能を向上させたり磁化の熱的な安定性を高めることができる。
【０１０５】
また前述したのスパッタターゲットを用いた本発明の製造方法は、垂直磁性層が、Ｃｏを主成分とし、少なくともＣｒ、Ｐｔ、Ｎｄを含んだ材料からなり、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓが０．８５以上であり、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントが０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕであることを特徴とする磁気記録媒体を容易に製造することができる。
【０１０６】
図５は、上記磁気記録媒体を用いた磁気記録再生装置の例を示すものである。ここに示す磁気記録再生装置は、図１に示す構成の磁気記録媒体５０と、磁気記録媒体５０を回転駆動させる媒体駆動部５１と、磁気記録媒体５０に情報を記録再生する磁気ヘッド５２と、この磁気ヘッド５２を磁気記録媒体５０に対して相対運動させるヘッド駆動部５３と、記録再生信号処理系５４とを備えている。記録再生信号処理系５４は、外部から入力されたデータを処理して記録信号を磁気ヘッド５２に送ったり、磁気ヘッド５２からの再生信号を処理してデータを外部に送ることができるようになっている。本発明の磁気記録再生装置に用いる磁気ヘッド５２には、再生素子として巨大磁気抵抗効果（ＧＭＲ）を利用したＧＭＲ素子などを有したより高記録密度に適したヘッドを用いることができる。
上記磁気記録再生装置によれば、垂直磁性層が、Ｃｏを主成分とし、少なくとも、Ｃｒ、Ｐｔ、Ｎｄを含んだ材料からなり、基板に対して垂直方向の残留磁化（Ｍｒ）と飽和磁化（Ｍｓ）との比Ｍｒ／Ｍｓが０．８５以上であり、活性化体積と飽和磁気モーメントの積で表される活性化磁気モーメントが０．３×１０^-15ｅｍｕ〜０．８×１０^-15ｅｍｕであることを特徴とする磁気記録媒体を用いているので、磁気記録媒体の記録再生時におけるノイズを増加させることなく、記録再生特性の分解能を向上させたり磁化の熱的な安定性を高めることができ、高記録密度に適した磁気記録再生装置となる。
【０１０７】
図４は、本発明の磁気記録媒体の第２の実施形態を示すもので、非磁性基板１と軟磁性下地層２との間に、磁気異方性が主に面内方向を向いた硬磁性層８を設けることができる。
【０１０８】
硬磁性層８にはＣｏＳｍ合金や、ＣｏＣｒＰｔＸ２合金（Ｘ２：Ｐｔ、Ｔａ、Ｚｒ、Ｎｂ、Ｃｕ、Ｒｅ、Ｎｉ、Ｍｎ、Ｇｅ、Ｓｉ、Ｏ、ＮおよびＢのうち１種または２種以上。）を用いるのが好適である。
【０１０９】
硬磁性層８は、保磁力Ｈｃが５００［Ｏｅ］以上（好ましくは１０００［Ｏｅ］以上）であることが好ましい。
【０１１０】
硬磁性層８の厚さは、１５０ｎｍ以下（好ましくは７０ｎｍ以下）であることが好ましい。硬磁性層８の厚さが１５０ｎｍを超えると、配向制御層３の表面平均粗さＲａが大きくなるため好ましくない。
【０１１１】
硬磁性層８は軟磁性下地層２と交換結合して、硬磁性層の磁化方向が基板半径方向であるものとするのが好ましい。その結果軟磁性層２の磁化が交換結合により半径方向に固着されるのでヘッドによる書き込み磁界と磁化の向きが直交することになり、記録再生時に交換結合状態がより安定する。その結果ノイズの発生を抑えることができるので好ましい。
【０１１２】
硬磁性層８を設けることにより、より効果的に軟磁性下地層２での巨大な磁区の形成を抑えることができるので、磁壁によるスパイクノイズの発生を防止して、記録再生時のエラーレートを十分に低くすることができる。
【０１１３】
硬磁性層８の配向を制御するために、非磁性基板１と硬磁性層８との間にＣｒ合金材料やＢ２構造材料を用いてもよい。
【０１１４】
以上の構成の磁気記録媒体を製造するには、基板１上に硬磁性層８を形成する工程を含ませ、その後スパッタ法などにより軟磁性下地層２を形成し、その後必要に応じてこの軟磁性下地層２の表面を酸化処理を施し、次いで配向制御層３、中間膜４、垂直磁性層５をスパッタ法などにより形成し、次いで保護層６をＣＶＤ法、イオンビーム法、スパッタ法などにより形成する。次いで、ディッピング法、スピンコート法などにより潤滑層７を形成する。
【０１１５】
例えば、硬磁性層を形成するには、従来の面内等方媒体を作成する方法を用いることができる。例えば、ガラス基板／ＮｉＡｌ合金層／ＣｒＭｏ合金層／ＣｏＣｒ合金層／ＣｏＣｒＰｔＢ合金層の構成を挙げることができる。次に、保護膜まで形成した磁気記録媒体に半径方向の磁場を印加して硬磁性層に半径方向の磁化を与える。印加する磁場の強さは、硬磁性層が充分に磁気的に飽和する磁界、例えば７９００００Ａ／ｍ（１００００[Ｏｅ]）以上が好ましい。
【０１１６】
【実施例】
以下、実施例を示して本発明の作用効果を明確にする。ただし、本発明は以下の実施例に限定されるものではない。
（実施例１）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に８９Ｃｏ４Ｚｒ７Ｎｂ（Ｃｏ含有量８９ａｔ％、Ｚｒ含有量４ａｔ％、Ｎｂ含有量７ａｔ％）のターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。
【０１１７】
次いで、基板を２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂ（Ｃｏ含有量６５ａｔ％、Ｃｒ含有量３０ａｔ％、Ｂ含有量５ａｔ％）ターゲットを用いて膜厚５ｎｍの中間膜４、６８Ｃｏ１８Ｃｒ１０Ｐｔ４Ｎｄ（Ｃｏ含有量６８ａｔ％、Ｃｒ含有量１８ａｔ％、Ｐｔ含有量１０ａｔ％、Ｎｄ含有量４ａｔ％）ターゲットを用いて膜厚２０ｎｍの垂直磁性層５を順次形成した。なお、上記スパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い、圧力０．６Ｐａにて成膜した。
次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。
（実施例２〜１１）
垂直磁性層５の組成と厚さを変えた以外は、実施例１と同様にして磁気記録媒体を作製した。
【０１１８】
（比較例１）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に８９Ｃｏ４Ｚｒ７Ｎｂのターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。
次いで、基板を２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂターゲットを用いて膜厚５ｎｍの中間膜４、７２Ｃｏ１８Ｃｒ１０Ｐｔターゲットを用いて２０ｎｍの垂直磁性層５を順次形成した。なお、上記スパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い、圧力０．６Ｐａにて成膜した。次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。
【０１１９】
（比較例２〜１２）
垂直磁性層５の組成と厚さを変えた以外は、比較例１と同様にして磁気記録媒体を作製した。
【０１２０】
実施例１〜１１、比較例１〜１２の磁気記録媒体の磁気特性を、振動式磁気特性測定装置（ＶＳＭ）にて測定した。なお、垂直方向の保磁力（Ｈｃ-ｖ）と面内方向の保磁力（Ｈｃ-ｉ）の比（Ｈｃ-ｖ）／（Ｈｃ-ｉ）の評価は以下のように実施した。軟磁性下地層を設けないサンプルを別途作成し、（Ｈｃ-ｖ）は、基板面に対して垂直方向に磁場が印加されるように、（Ｈｃ-ｉ）は、基板面に平行な方向、かつ円周方向もしくは径方向に対して磁場が印加されるようにして測定してその比を算出した。
【０１２１】
また、ｖＩｓｂの評価結果を、振動式磁気特性測定装置を用い、垂直方向の保磁力の時間依存データを測定し、前述した式より算出した。
【０１２２】
また記録再生特性を、ＧＵＺＩＫ社製リードライトアナライザーＲＷＡ１６３２、およびスピンスタンドＳ１７０１ＭＰを用いて測定した。電磁変換特性の評価には、再生部に巨大磁気抵抗（ＧＭＲ）素子を有する複合型薄膜磁気記録ヘッドを用い、記録条件を線記録密度５００ｋＦＣＩとして測定を行った。
【０１２３】
熱揺らぎ耐性（熱減磁）については、スピンスタンドＳ１７０１ＭＰを用い、７０℃において線記録密度５０ｋＦＣＩで書きこみを行った後、書きこみ後１秒後の再生出力に対する出力の低下率（％／ｄｅｃａｄｅ）を、（Ｓｏ−Ｓ）×１００／（Ｓｏ×３）に基づいて算出した。この式において、Ｓｏは磁気記録媒体に信号記録後１秒経過時の再生出力をしめし、Ｓは１０００秒後の再生出力を示す。結果を表２に示す。
【０１２４】
（実施例１２）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に８９Ｃｏ４Ｚｒ７Ｎｂのターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。
次いで、基板を２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂターゲットを用いて膜厚５ｎｍの中間膜４、５８Ｃｏ２２Ｃｒ１４Ｐｔ２Ｂ４Ｎｄターゲットを用いて膜厚２０ｎｍの垂直磁性層５を順次形成した。なお、上記スパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い、圧力０．６Ｐａにて成膜した。
次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。
【０１２５】
（実施例１３〜１６）
垂直磁性層５の組成を変えた以外は実施例１２と同様にして磁気記録媒体を作成した。
【０１２６】
（比較例１３、１４）
垂直磁性層５の組成を変えた以外は比較例１と同様にして磁気記録媒体を作成した。実施例１２〜１６、比較例１３、１４の磁気記録媒体の磁気特性、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、ｖＩｓｂを実施例１と同様に測定、評価した。
結果を表３に示す。
【０１２７】
（実施例１７）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に８９Ｃｏ４Ｚｒ７Ｎｂのターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。
次に、表面を酸素ガスに曝した。暴露は、暴露ガスとして５０％酸素−アルゴン混合ガスを用い、圧力１Ｐａ状態に１０ｓｅｃ間放置の条件で行った。
次いで、基板２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂターゲットを用いて膜厚５ｎｍの中間膜４を形成した。さらに一番目の垂直磁性層５１として６３Ｃｏ１８Ｃｒ１４Ｐｔを膜厚１５ｎｍ、さらに二番目の垂直磁性層５２として５９Ｃｏ２２Ｃｒ１４Ｐｔ５Ｎｄターゲットを用いて膜厚５ｎｍを順次形成した。なお、上記スパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い、圧力０．６Ｐａにて成膜した。
次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。
【０１２８】
（実施例１８、１９）
一番目の垂直磁性層５１を表４のように変えた他は、実施例１７と同様にして磁気記録媒体を作成した。
実施例１７、１８、１９の磁気記録媒体の磁気特性、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、ｖＩｓｂを実施例１と同様に測定、評価した。
結果を表４に示す。
【０１２９】
（実施例２０）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に硬磁性層８の配向を制御するための９４Ｃｒ６Ｍｏを膜厚２０ｎｍ成膜し、さらに硬磁性層８としてＣｏ２０Ｃｒ１４Ｐｔ４Ｂを膜厚５０ｎｍに形成した。次に８９Ｃｏ４Ｚｒ７Ｎｂのターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。
次に、表面を酸素ガスに曝した。暴露は、暴露ガスとして５０％酸素−アルゴン混合ガスを用い、圧力１Ｐａの雰囲気に１０ｓｅｃ間放置の条件で行った。
次いで、基板２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂターゲットを用いて膜厚５ｎｍの中間膜４、５９Ｃｏ２２Ｃｒ１４Ｐｔ５Ｎｄターゲットを用いて膜厚２０ｎｍの垂直磁性層５を順次形成した。なお、上記スパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い、圧力０．６Ｐａにて成膜した。次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。得られた磁気記録媒体を、１０ｍｓｅｃオーダーの反値幅を有するパルス磁界を発生させる磁気記録媒体専用の着磁ジグに２００Ｖの電圧を印加して、半径方向に９４８ｋＡ／ｍ（１１８５０［Ｏｅ］）の強度のパルス磁界を印加し、半径方向に磁化固着を行った。
【０１３０】
（実施例２１〜２４）
硬磁性層層の組成および膜厚を変えた他は、実施例２０と同様にして磁気記録媒体を作成した。実施例２０〜２４の磁気記録媒体の磁気特性、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、ｖＩｓｂを実施例１と同様に測定、評価した。
結果を表５に示す。
【０１３１】
（実施例２５）
洗浄済みのガラス基板（オハラ社製、外直径２．5インチ）をＤＣマグネトロンスパッタ装置（アネルバ社製Ｃ−３０１０）の成膜チャンバ内に収容して、到達真空度１×１０^-5Ｐａとなるまで成膜チャンバ内を排気した後、このガラス基板上に８９Ｃｏ４Ｚｒ７Ｎｂのターゲットを用いて１００℃以下の基板温度で膜厚１００ｎｍの軟磁性下地層２をスパッタにより成膜した。この膜の飽和磁束密度Ｂｓ（Ｔ）と膜厚ｔ（ｎｍ）の積Ｂｓ・ｔ（Ｔ・ｎｍ）が１２０（Ｔ・ｎｍ）であることを振動式磁気特性測定装置（ＶＳＭ）で確認した。次いで、基板を２００℃に加熱して、上記軟磁性下地層上に、Ｒｕターゲットを用いて膜厚２０ｎｍの配向制御層３を形成し、６５Ｃｏ３０Ｃｒ５Ｂターゲットを用いて膜厚５ｎｍの中間膜４、５９Ｃｏ２２Ｃｒ１４Ｐｔ５Ｎｄターゲットを用いて膜厚２０ｎｍの垂直磁性層５を順次形成した。なお、垂直磁性層５を成膜するスパッタ工程においては、成膜用のスパッタガスとしてアルゴンを用い圧力３Ｐａにて成膜した。その他の成膜のスパッタ工程においては、０．６Ｐａにて成膜した。次いで、ＣＶＤ法により膜厚５ｎｍの保護層６を形成した。次いで、ディッピング法によりパーフルオロポリエーテルからなる潤滑層７を形成し、磁気記録媒体を得た。
【０１３２】
（実施例２６〜２８）
垂直磁性層５の成膜圧力を変えた他は、実施例２４と同様にして磁気記録媒体を作成した。実施例２５〜２８の磁気記録媒体の磁気特性、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、ｖＩｓｂを実施例１と同様に測定、評価した。
結果を表６に示す。
【０１３３】
【表２】

【０１３４】
表２より、垂直磁性層５にNdを添加した磁性材料を使うことで、ｖＩｓｂの増加を抑え、Ｍｒ／Ｍｓ比、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、−Ｈｎが向上し、結果として記録再生時の分解能、Ｓ／Ｎ比そして熱揺らぎ特性が改善していることがわかる。実施例１はＮｄの添加により、Ｎｄを添加していない比較例１よりも、Ｍｒ／Ｍｓ比、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、−Ｈｎが向上している。また、実施例１と同等な磁気特性を得るのに、Ｐｔを増加させた比較例１〜５では、Ｐｔを２０ａｔ％まで添加する必要がある上、Ｐｔ量の増加によりｖＩｓｂが大きくなり、結果として記録再生時におけるＳ／Ｎ比が低下することがわかる。一方、実施例７〜９より、Ｎｄ含有量を増加ることで、ｖＩｓｂをほとんど増加させることなく、Ｍｒ／Ｍｓ比、（Ｈｃ-ｖ）／（Ｈｃ-ｉ）、−Ｈｎをさらに向上させることができることがわかる。これより、磁気記録媒体の磁気特性を向上させるのに、Ｐｔを増加させるよりもＮｄを添加するほうが効果的であることがわかる。比較例６〜８より、Ｃｒ含有量が１８〜２８ａｔ％の範囲をはずれた場合、Ｎｄの添加量が８ａｔ％を超えた場合、Ｍｒ／Ｍｓ比や熱揺らぎ耐性が低下したり、ｖＩｓｂが増加し、記録再生時におけるＳ／Ｎ比が低下することがわかる。比較例９より、Ｐｔ量が１０ａｔ％より少ない場合、Ｎｄ添加の効果はほとんど得られない。また、比較例１０より、Ｐｔ量が２０ａｔ％を超える場合、急激に磁気特性が低下することがわかる。
【０１３５】
【表３】

【０１３６】
垂直磁性層５を形成する磁性材料にＮｄを添加した上、さらにＣｕ、Ｂ、Ｔａを添加することで磁気特性の制御が可能である。ただし、比較例９、１０に見られるように、Ｃｕ、Ｂ、Ｔａの合計含有量が８ａｔ％を超えると、磁気特性が低下することがわかる。
【０１３７】
【表４】

【０１３８】
垂直磁性層５を複数設け、その内の１層をＮｄを添加した磁性材料とすることで、磁気特性が向上することがわかる。
【０１３９】
【表５】

【０１４０】
硬磁性層８として、各種材料が使用可能であることがわかる。
【０１４１】
【表６】

【０１４２】
垂直磁性層５の成膜時のスパッタガス圧力を高くすることで、他の特性を損ねることなく、ｖＩｓｂがより小さくできることがわかる。実施例２８から、成膜圧力が２０Ｐａを超えると、磁気特性が低下することがわかる。
【０１４３】
【発明の効果】
以上説明したように、本発明の磁気記録媒体にあっては、垂直磁性層がＣｏを主成分とし、少なくともＣｒ、Ｐｔ、Ｎｄを含んだ材料から形成することにより、記録再生特性を損ねることなく、磁気特性を向上させることができる。さらに、Ｐｔの替わりにＮｄ含有量を制御することで磁気特性を向上させることができるので、垂直磁性層中のＰｔ含有量を減らすことができ、磁気記録媒体の製造コストの上昇を防ぐことができる。
【図面の簡単な説明】
【図１】本発明の磁気記録媒体の第一の実施形態を示す断面図である。
【図２】磁化曲線の一例を示す図である。
【図３】磁化曲線の他の例を示す図である。
【図４】本発明の第二の実施形態を示す断面図である。
【図５】本発明の磁気記録媒体を用いた磁気記録再生装置の一例を示す概略構成図である。
【符号の説明】
１…非磁性基板、２…軟磁性下地層、３…配向制御層、４…中間層、５…垂直磁性層、６…保護層、７…潤滑層、８…硬磁性層
５０：磁気記録媒体、５１：媒体駆動部、５２：磁気ヘッド、５３：ヘッド駆動部、５４：記録再生信号処理系[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium used in a hard disk device or the like, a method for manufacturing the magnetic recording medium, and a magnetic recording / reproducing apparatus, and particularly relates to an excellent recording / reproducing characteristic.
[0002]
[Prior art]
A hard disk drive (HDD), which is a type of magnetic recording / reproducing device, is currently said to have a recording density that increases at an annual rate of 60% or more, and this trend is said to continue. For this purpose, development of a magnetic recording head suitable for high recording density and development of a magnetic recording medium have been promoted.
[0003]
Most of magnetic recording media for hard disk devices currently on the market are in-plane magnetic recording media in which the easy magnetization axis in the magnetic layer is oriented mainly horizontally with respect to the substrate. Here, the easy magnetization axis is an axis in which the magnetization is easily oriented, and in the case of a Co-based alloy, it is the c-axis of the hcp structure of Co.
[0004]
In such an in-plane magnetic recording medium, it is said that when the recording density is increased, the volume of the magnetic layer per bit becomes too small, and the recording / reproducing characteristics may be deteriorated due to the thermal fluctuation effect. Further, when the recording density is increased, it is said that the medium noise increases due to the influence of the demagnetizing field generated at the boundary of the recording bits.
[0005]
In contrast, a so-called perpendicular magnetic recording medium in which the easy axis of magnetization in the magnetic layer is oriented mainly perpendicularly has a low demagnetizing field at the bit boundary even when the recording density is increased, and the recording magnetic domain has a sharp boundary. Therefore, even if the recording density is increased, the bit volume can be made relatively large, so that the thermal fluctuation effect is strong. Thus, in recent years, much attention has been paid and a medium structure suitable for perpendicular magnetic recording has been proposed.
[0006]
[Problems to be solved by the invention]
In recent years, in response to the demand for higher recording density of magnetic recording media, it has been studied to use a single pole head having excellent writing ability for the perpendicular magnetic layer. In order to cope with such a head, a layer made of a soft magnetic material called a backing layer is provided between the perpendicular magnetic layer, which is a recording layer, and the substrate, so that the single-pole head and the magnetic recording medium are provided. There has been proposed a magnetic recording medium in which the efficiency of entering and exiting the magnetic flux is improved.
[0007]
However, in the case of using a magnetic recording medium simply provided with a backing layer as described above, the recording / reproducing characteristics at the time of recording / reproducing, the heat-resistant demagnetization resistance, and the recording resolution are not satisfactory, and the magnetic properties excellent in these characteristics are obtained. A recording medium has been desired.
[0008]
Japanese Patent Laid-Open No. 2-103715 proposes to add a rare earth element such as Nd as a third element in a perpendicular magnetic layer of a Co—Cr alloy. However, by simply adding Nd to a Co—Cr alloy, the coercive force, the ratio Mr / Ms of the remanent magnetization (Mr) and the saturation magnetization (Ms), the reverse domain nucleation magnetic field (−Hn), the perpendicular magnetic anisotropy (Hc-v) / (Hc-i) (coercivity in the direction perpendicular to the substrate: (Hc-v), coercivity of the plane parallel to the substrate: (Hc-i)) The improvement effect is insufficient. However, even if more Nd is added, the effect of improving the magnetic characteristics due to an increase in Ku cannot be obtained. On the contrary, there is a possibility that a bad effect such as deterioration in recording and reproducing characteristics due to an increase in noise may be caused.
[0009]
In order to increase the Ku (magnetic anisotropy constant) of the Co alloy of the magnetic layer, generally, a method of containing a large amount of Pt (16 to 26 at%) in the Co alloy is used. When a material containing a large amount of is used, noise due to excessive magnetic interparticle interaction in the magnetic layer becomes large, and the characteristics are not suitable for high-density recording.
[0010]
Therefore, a magnetic material capable of suppressing an increase in noise while increasing Ku in the vertical direction and a magnetic recording medium having such characteristics are desired.
[0011]
The present invention has been made in view of the above circumstances, and provides a magnetic recording medium capable of recording / reproducing high-density information with improved recording / reproducing characteristics and thermal fluctuation resistance, a method for manufacturing the same, and a magnetic recording / reproducing apparatus. The purpose is to do.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors of the present invention relate to a technique for adding Nd to a magnetic material containing Co as a main component and containing Cr and Pt, and the relationship between the combination of the content of each element and the recording / reproduction characteristics of the medium The present invention based on the following constitution was completed.
1) A first invention for solving the above problems is that a nonmagnetic substrate has at least an orientation control layer for controlling the orientation of the layer immediately above and an easy magnetization axis oriented perpendicularly to the substrate. A perpendicular magnetic layer and a protective layer are provided. The perpendicular magnetic layer is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, and has a residual magnetization (Mr) and saturation perpendicular to the substrate. The ratio (Mr / Ms) to the magnetization (Ms) is 0.85 or more, and the activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 The magnetic recording medium is emu.
2) The second invention for solving the above-mentioned problems is that the coercive force in the vertical direction with respect to the substrate is 2500 [Oe] or more, and the coercive force (Hc-v) in the vertical direction is parallel to the substrate. The magnetic recording medium according to 1), wherein the surface coercivity (Hc-i) ratio (Hc-v) / (Hc-i) is 5 or more.
3) A third invention for solving the above-mentioned problems is that the reverse magnetic domain nucleation magnetic field in the direction perpendicular to the substrate is 0 to 2000 [Oe]. It is a recording medium.
4) According to a fourth invention for solving the above problem, the perpendicular magnetic layer has a Cr content of 18 to 28 at%, a Pt content of 10 to 20 at%, and an Nd content of 0.5 to 8 at%. The magnetic recording medium according to any one of 1) to 3), wherein the magnetic recording medium is made of a material.
5) According to a fifth invention for solving the above-mentioned problem, the perpendicular magnetic layer includes one or more selected from B, Ta, and Cu, and the total content of these elements is 8 at% or less. The magnetic recording medium according to any one of 1) to 4), wherein:
6) In a sixth invention for solving the above-mentioned problem, the perpendicular magnetic layer is composed of a plurality of magnetic layers, and at least one of the layers is composed of the perpendicular magnetic layer according to any one of 1) to 5). This is a magnetic recording medium.
7) In a seventh invention for solving the above-mentioned problem, the uppermost magnetic layer of the perpendicular magnetic layer composed of a plurality of magnetic layers is composed of the perpendicular magnetic layer according to any one of 1) to 6). This is a magnetic recording medium.
8) An eighth invention for solving the above problems is characterized in that a soft magnetic underlayer made of a soft magnetic material is provided between the nonmagnetic substrate and the orientation control layer. The magnetic recording medium according to any one of the above.
9) A ninth invention for solving the above-mentioned problems is the magnetic recording medium according to any one of 1) to 8), wherein the surface of the soft magnetic layer is oxidized or nitrided. .
10) A tenth invention for solving the above-mentioned problem is characterized in that a hard magnetic layer having magnetic anisotropy mainly in an in-plane direction is provided between a nonmagnetic substrate and a soft magnetic underlayer. 8) or 9).
11) An eleventh invention for solving the above-mentioned problems is that the hard magnetic layer is made of a CoSm alloy or a CoCrPtX2 alloy (X2: Pt, Ta, Zr, Nb, Cu, Re, Ni, Mn, Ge, Si, O , N, and B)), and has a coercive force of 500 [Oe] or more and a magnetization direction in a radial direction of the substrate. It is a recording medium.
12) A twelfth aspect of the invention for solving the above-described problem is that an orientation control layer for controlling the orientation of at least a layer immediately above the nonmagnetic substrate and an easy magnetization axis are mainly perpendicular to the substrate. In a method of manufacturing a perpendicular magnetic recording medium including a step of sequentially forming an oriented perpendicular magnetic layer and a protective layer,
In the step of forming the perpendicular magnetic layer by the sputtering method, it is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, with a Cr content of 18 to 28 at% and a Pt content of 10 to 20 at%. , Using a sputtering target having an Nd content of 0.5 to 8 at%.
13) A method for manufacturing a magnetic recording medium according to 12), characterized in that the pressure of the sputtering gas in the step of forming the perpendicular magnetic layer is 3 to 20 Pa in the thirteenth invention for solving the above-mentioned problem. It is.
14) A fourteenth invention for solving the above-mentioned problems is that, before the step of forming the orientation control layer, after forming the soft magnetic layer and forming the soft magnetic layer, the surface thereof is oxygen gas, nitrogen gas. The method for producing a magnetic recording medium according to 12) or 13), comprising a step of exposing to any gas selected from a mixed gas thereof or a gas containing them.
15) A fifteenth invention for solving the above-mentioned problems is a magnetic recording / reproducing apparatus comprising a magnetic recording medium and a magnetic head for recording / reproducing information on the magnetic recording medium, wherein the magnetic recording medium is 1) A magnetic recording / reproducing apparatus comprising the magnetic recording medium according to any one of items 1 to 11).
In this specification, a main component is an element with the largest content in the alloy. Preferably, the main component is one whose content exceeds 50 at% in the alloy.
[0013]
In the present invention, the magnetic material contains at least Cr, Pt, and Nd. The effect of adding Nd in the presence of Pt makes it possible to suppress the amount of Pt added to obtain good magnetic properties, so that recording / reproduction of a magnetic recording medium becomes a problem when the Pt content increases. It is possible to improve the resolution of the recording / reproducing characteristics and increase the thermal stability of magnetization without increasing noise at the time.
[0014]
The effect of Nd addition will be described with reference to Table 1.
[0015]
[Table 1]

When a Ru film having a thickness of 20 nm is formed as an orientation control layer on a non-magnetic substrate, and a film made of a magnetic material having the composition shown in Table 1 is formed thereon with a thickness of 20 nm as a perpendicular magnetic recording layer. Table 1 shows the magnetic characteristics and recording / reproducing characteristics.
[0016]
The coercive force shown in Table 1 means the coercive force in the vertical direction. The larger the value, the better the resolution characteristics at the time of recording and reproduction, and the thermal stability of magnetization increases. The value of the ratio (Mr / Ms) is an index representing the thermal stability of magnetization of the magnetic layer. Further, -Hn is an index representing the thermal stability of magnetization of the magnetic layer, and (Hc-v) / (Hc-i) is the easy axis of magnetization of the Co alloy crystal constituting the magnetic layer in the direction perpendicular to the substrate. It is an index that shows how much you have.
[0017]
Further, vIsb represents an activation magnetic moment and is closely related to the magnitude of noise during recording and reproduction, and the smaller this value, the smaller the noise. Here, the activation magnetic moment (vIsb) is calculated as follows based on the time-dependent characteristic measurement data of the coercive force (Hc-v) in the perpendicular direction of the perpendicular magnetic layer using VSM. The temperature condition at the time of measurement can be room temperature.
[0018]
(I) Substituting time-dependent characteristic measurement data into the following Sharlock equation (for example, J. Appl. Phys. 62 (7), p2918), and (Ku × V) / (k × T). Ask.
[0019]
[Expression 1]

[0020]
A = 1 × 10 ⁹ , N = 0.5, k: Boltzmann constant, Hc0: theoretical maximum coercivity
[0021]
Specifically, it can be obtained as follows.
(1) The time t per loop for measuring the magnetization curve is changed at several points (for example, 30 seconds, 60 seconds, 180 seconds, 300 seconds, 600 seconds), and the coercive force (Hc ) As a measuring device for the magnetization curve, a commonly used magnetic property measuring device based on the VSM or Kerr effect can be used.
[0022]
(2) When changing in m ways, m combinations of data (measurement time, coercive force) are obtained.
[0023]
(3) These data are converted into {ln (A × t / 0.635)} ^0.5 Is plotted on a graph with the X axis and Hc the Y axis.
[0024]
(4) An approximate straight line is obtained from the plotted data.
[0025]
(5) Hc0 × (k × T / Ku × V) from the slope of the approximate line ^0.5 Read Hc0 from the Y-axis intercept.
[0026]
(6) From this, (Ku × V / k × T) is obtained.
[0027]
(II) Next, the obtained magnetic moment (vIsb) is obtained by substituting the obtained (Ku × V / k × T) into the following equation.
[0028]
[Expression 2]

[0029]
Samples 1 to 5 in Table 1 have a fixed Cr content and an increased Pt content. As a result, the coercive force (Hc) and the (Mr / Ms) ratio are increasing. Although −Hn is increased, no change is observed in (Hc−v) / (Hc−i) representing the perpendicular magnetic anisotropy of the magnetic layer. Rather, the value of vIsb, which is closely related to noise during recording / reproduction, is increasing.
[0030]
When the method of increasing the Pt content is used to improve the magnetic properties of the perpendicular magnetic layer, the resolution and thermal stability can be improved, but on the other hand, the crystal orientation of the magnetic layer should be improved. This means that noise increases due to an increase in interaction between magnetic particles.
[0031]
On the other hand, as shown in Samples 6 to 10 in Table 1, when Nd is added instead of Pt and the amount added is increased, the Hc and Mr / Ms ratios are increased as with Pt. It can also be seen that -Hn can be increased. Since the value of (Hc-v) / (Hc-i) is also increased, it is estimated that the crystal orientation of the magnetic layer is improved, and as a result, Hc, Mr / Ms, and -Hn are improved. it is conceivable that. The point to be noted here is that an increase in the value of vIsb can be suppressed while these characteristics are improved. According to the present invention in which Nd is added to a magnetic material in the presence of Pt, (Hc-v) / (Hc-i) is improved without increasing noise during recording and reproduction, and Hc, Mr / Ms, -Hn. It can be seen that the magnetic characteristics are improved.
[0032]
Further, when Nd is added in excess of 8 at%, the magnetic properties are deteriorated. On the other hand, even if Nd is added to a magnetic material composed only of CoCr or a magnetic material having a Pt content of less than 10 at%, the magnetic characteristics are deteriorated. This is presumably because the magnetic anisotropy constant (Ku) of the underlying magnetic material is small, so that the effect of improving magnetic properties is small. From this, it can be seen that it is preferable to add Nd in the presence of 10 at% or more of Pt in order to obtain an Nd improvement effect more effectively.
[0033]
The reason why the magnetic properties are improved by adding Nd is not completely clear, but can be estimated as follows. When Nd is added to a magnetic material containing Co as a main component, a Co and Nd metal compound (NdCo5, Nd2Co17, etc.) may be formed by a part of Co and Nd. These metal compounds of Nd and Co have the same composition as the raw material of the rare earth-cobalt magnet, and it is known that an alloy having that composition has a large value of crystal magnetic anisotropy and magnetic anisotropy constant (Ku). By forming this compound, the magnetic anisotropy constant (Ku) of the entire magnetic layer is improved, and the perpendicular magnetic anisotropy is achieved by orienting the easy magnetization axis of these crystals in the direction perpendicular to the substrate. The value of (Hc−v / Hc−i) increases. As a result, it is considered that the magnetic properties represented by the coercive force (Hc), Mr / Ms ratio, and -Hn of the whole perpendicular magnetic layer are improved. Further, unlike the case where the amount of Pt added is simply increased, the addition of Nd does not hinder Cr segregation, so there is no effect of increasing the size of magnetic particles or increasing the interaction between magnetic particles. It is considered that noise during reproduction is not increased.
[0034]
Here, if Pt is not present, the magnetic particles do not have a certain degree of magnetic anisotropy, and therefore the influence of the demagnetizing field is large in the magnetization reversal. As a result, the coercive force required for high-density recording and It is considered difficult to obtain magnetic characteristics such as Mr / Ms and -Hn.
[0035]
In the magnetic recording medium of the present embodiment, the perpendicular magnetic layer 5 is made of a material containing at least Cr and Pt containing Co as a main component, and further formed from a magnetic material to which Nd is added. Then, the ratio Mr / Ms between the residual magnetization (Mr) and the saturation magnetization (Ms) in the vertical direction is 0.85 or more, and the activation magnetic moment expressed by the product of the activation volume and the saturation magnetic moment is 0.3 ×. 10 ^-15 emu ~ 0.8 × 10 ^-15 emu.
[0036]
Further, by providing an intermediate film having an hcp structure between the orientation control layer and the magnetic layer, the ratio Mr / Ms of remanent magnetization (Mr) and saturation magnetization (Ms), coercive force (Hc-v), vertical direction The ratio (Hc-v) / (Hc-i) of the coercive force (Hc-v) and the coercive force (Hc-i) in the in-plane direction, and the reverse domain nucleation magnetic field (-Hn) are improved.
[0037]
As a result, the resolution and the thermal fluctuation resistance during recording / reproduction are greatly improved, and the increase in the activation magnetic moment (vIsb) is suppressed, so that the noise required during recording / reproduction is reduced, and the signal necessary for high-density recording. Since the / noise ratio (S / N) can be secured, the magnetic recording medium of the present invention is a magnetic recording medium with improved recording / reproducing characteristics.
[0038]
The thermal fluctuation is a phenomenon in which the recording bit becomes unstable and the recorded data is thermally lost, and in a magnetic recording medium device, it appears as a decay of the reproduction / reproduction output of the recorded data with time.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a first embodiment of a magnetic recording medium according to the present invention. The magnetic recording medium shown here includes a soft magnetic underlayer 2, an orientation control layer 3, an intermediate layer on a nonmagnetic substrate 1. The layer 4, the perpendicular magnetic layer 5, the protective layer 6, and the lubricating layer 7 are sequentially formed.
[0040]
As the nonmagnetic substrate 1, a metal substrate made of a metal material such as aluminum or an aluminum alloy may be used, or a nonmetal substrate made of a nonmetal material such as glass, ceramic, silicon, silicon carbide, or carbon may be used. Good.
[0041]
As the glass substrate, there are amorphous glass and crystallized glass, and general-purpose soda-lime glass, aluminosilicate glass, and aluminosilicate glass can be used as the amorphous glass. Further, as the crystallized glass, lithium-based crystallized glass can be used. As the ceramic substrate, a sintered body mainly composed of general-purpose aluminum oxide, aluminum nitride, silicon nitride, or the like, or a fiber reinforced material thereof can be used.
[0042]
As the non-magnetic substrate 1, the above-described metal substrate or a non-metal substrate having a NiP layer formed by plating or sputtering may be used.
[0043]
In the present invention, it is preferable to provide the soft magnetic layer 2 under the orientation control layer. The soft magnetic underlayer 2 increases the vertical component of the magnetic flux emitted from the head with respect to the substrate, and more firmly fixes the magnetization direction of the perpendicular magnetic layer 5 on which information is recorded in the direction perpendicular to the substrate 1. Because it can be done. This effect becomes particularly prominent when a single pole head for perpendicular recording is used as a magnetic head for recording and reproduction.
[0044]
The soft magnetic underlayer 2 is made of a soft magnetic material, and as this material, a material containing Fe, Ni, Co can be used. As this material, FeCo alloy (FeCo, FeCoV), FeNi alloy (FeNi, FeNiMo, FeNiCr, FeNiSi), FeAl alloy (FeAl, FeAlSi, FeAlSiCr, FeAlSiTiRu, FeAlO), FeCr alloy (FeCr, FeCrTi, FeCrCu), FeTa alloy (FeTa, FeTaC, FeTaN), FeMg alloy (FeMgO), FeZr alloy (FeZrN), FeC alloy, FeN alloy, FeSi alloy, FeP alloy, FeNb alloy, FeHf alloy An alloy and a FeB type alloy can be mentioned.
[0045]
Alternatively, a material having a fine crystal structure such as FeAlO, FeMgO, FeTaN, FeZrN, or the like containing 60 at% or more of Fe, or a material having a granular structure in which fine crystal particles are dispersed in a matrix may be used.
[0046]
As a material for the soft magnetic underlayer 2, in addition to the above, a Co alloy containing 80 at% or more of Co, containing at least one of Zr, Nb, Ta, Cr, Mo, etc. and having an amorphous structure should be used. Can do. Preferred examples of this material include CoZr, CoZrNb, CoZrTa, CoZrCr, and CoZrMo alloys.
[0047]
The coercive force Hc of the soft magnetic underlayer 2 is preferably 200 [Oe] or less (preferably 50 [Oe] or less). When the coercive force Hc exceeds the above range, the soft magnetic characteristics are insufficient, and the reproduced signal waveform is changed from a so-called rectangular wave to a distorted waveform, which is not preferable.
[0048]
The saturation magnetic flux density Bs of the soft magnetic underlayer 2 is preferably 0.6 T or more (preferably 1 T or more). If this Bs is less than the above range, the reproduced signal waveform is not preferable because it becomes a waveform having distortion from a so-called rectangular wave.
[0049]
The thickness of the soft magnetic layer is preferably 50 to 400 nm. This is because a waveform having no distortion in the reproduced signal waveform can be obtained within this range.
[0050]
The product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) of the soft magnetic underlayer 2 and the layer thickness t (nm) of the soft magnetic underlayer 2 is 20 (T · nm) or more (preferably 40 (T · nm) or more). If this Bs · t is less than the above range, the reproduced signal waveform becomes distorted or the OW characteristics deteriorate, which is not preferable.
[0051]
The outermost surface (surface on the orientation control layer 3 side) of the soft magnetic underlayer 2 is preferably configured by partially or completely oxidizing the material constituting the soft magnetic underlayer 2. That is, the material constituting the soft magnetic underlayer 2 is partially oxidized on the surface of the soft magnetic underlayer 2 (surface on the orientation control layer 3 side) and the vicinity thereof, or an oxide of the material is formed. Are preferably arranged. Thereby, since the magnetic fluctuation of the surface of the soft magnetic underlayer 2 can be suppressed, the noise caused by the magnetic fluctuation can be reduced and the recording / reproducing characteristics of the magnetic recording medium can be improved. Further, the recording / reproducing characteristics can be improved by refining the crystal grains of the orientation control layer 3 formed on the soft magnetic underlayer 2.
[0052]
The oxidized portion of the surface of the soft magnetic underlayer 2 is formed by, for example, forming the soft magnetic underlayer 2 and then exposing it to an atmosphere containing oxygen, or forming a portion close to the surface of the soft magnetic underlayer 2. It can be formed by a method of introducing oxygen during the process. Specifically, when the surface of the soft magnetic underlayer 2 is exposed to oxygen, it should be kept for about 0.3 to 20 seconds in a gas atmosphere in which oxygen alone or oxygen is diluted with a gas such as argon or nitrogen. That's fine. It can also be exposed to the atmosphere. In particular, when a gas obtained by diluting oxygen with a gas such as argon or nitrogen is used, the degree of oxidation on the surface of the soft magnetic underlayer 2 can be easily adjusted, so that stable production can be performed. When oxygen is introduced into the gas for forming the soft magnetic underlayer 2, for example, if a sputtering method is used as the film forming method, a process gas in which oxygen is introduced into only a part of the film forming time is used. Sputtering may be performed. As this process gas, for example, a gas in which oxygen is mixed in an amount of 0.05% to 50% (preferably 0.1 to 20%) by volume with argon is suitably used.
[0053]
The orientation control layer 3 controls the orientation and grain size of the intermediate layer 4 and the perpendicular magnetic layer 5 provided immediately above.
[0054]
The material is not particularly limited, but a material having an hcp structure, an fcc structure, or an amorphous structure is preferable. In particular, Ru alloys, Ni alloys, and Co alloys are particularly preferable.
[0055]
In the magnetic recording medium of this embodiment, the thickness of the orientation control layer 3 is preferably 0.5 to 40 nm (preferably 1 to 20 nm). When the thickness of the orientation control layer 3 is in the range of 0.5 to 40 nm (preferably 1 to 20 nm), the perpendicular orientation of the perpendicular magnetic layer 5 is particularly high, and the magnetic head and soft magnetic underlayer during recording are recorded. Since the distance to 2 can be reduced, the recording / reproduction characteristics can be improved without reducing the resolution of the reproduction signal. When this thickness is less than the above range, the perpendicular orientation in the perpendicular magnetic layer 5 is lowered, and the recording / reproducing characteristics and the resistance to thermal fluctuation are deteriorated. On the other hand, if the thickness exceeds the above range, the magnetic particle diameter of the perpendicular magnetic layer 5 is increased, and noise characteristics may be deteriorated. Further, since the distance between the magnetic head and the soft magnetic underlayer 2 at the time of recording becomes large, the resolution of the reproduction signal and the reproduction output are lowered, which is not preferable.
[0056]
Since the surface shape of the orientation control layer 3 affects the surface shapes of the perpendicular magnetic layer 5 and the protective layer 6, the surface irregularity of the magnetic recording medium is reduced to reduce the flying height of the magnetic head during recording and reproduction. The surface average roughness Ra of the orientation control layer 3 is preferably 2 nm or less. By setting the average surface roughness Ra to 2 nm or less, the surface roughness of the magnetic recording medium can be reduced, the flying height of the magnetic head during recording and reproduction can be sufficiently lowered, and the recording density can be increased.
[0057]
Oxygen or nitrogen may be introduced into the gas for forming the orientation control layer 3. For example, if a sputtering method is used as the film forming method, the process gas may be argon mixed with oxygen in a volume ratio of 0.05 to 50% (preferably 0.1 to 20%), argon and nitrogen. Is preferably used in a volume ratio of 0.01 to 20% (preferably 0.02 to 10%).
[0058]
An intermediate layer 4 can be provided between the orientation control layer 3 and the perpendicular magnetic layer 5. By providing the intermediate layer 4, the perpendicular orientation of the perpendicular magnetic layer 5 can be enhanced, so that the coercive force of the perpendicular magnetic layer 5 can be enhanced, and the recording / reproducing characteristics and the thermal fluctuation resistance can be further improved.
[0059]
It is preferable to use a material having an hcp structure for the intermediate layer 4. The intermediate layer 4 includes a CoCr alloy, a CoCrX1 alloy, a CoX1 alloy (X1: Pt, Ta, Zr, Ru, Nb, Cu, Re, Ni, Mn, Ge, Si, O, N, and B or It is preferable to use two or more).
[0060]
The Co content in the intermediate layer 4 is preferably 30 to 70 at%. This is because the intermediate layer is nonmagnetic within this range.
[0061]
The thickness of the intermediate layer 4 does not cause deterioration in recording / reproducing characteristics due to the coarsening of the magnetic particles in the perpendicular magnetic layer 5 or decrease in recording resolution due to an increase in the distance between the magnetic head and the soft magnetic underlayer 2. Therefore, the thickness is preferably 20 nm or less (preferably 10 nm or less).
[0062]
The perpendicular magnetic layer 5 has an axis of easy magnetization mainly oriented in a direction perpendicular to the substrate, and is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd. As the content of each element, the Cr content is 18 to 28 at% (preferably 19 to 24 at%), the Pt content is 10 to 20 at% (preferably 13 to 18 at%), and the Nd content is 0.5. It is preferable that it is -8at% (preferably 1-4at%).
[0063]
When the content of Cr is less than 18 at%, the thickness of the grain boundary layer formed between the magnetic particles due to Cr segregation is reduced, so that the magnetic interparticle interaction between the magnetic particles is increased. The particle size of the magnetic particles themselves is also likely to be enlarged. As a result, noise during recording / reproduction increases, and a signal / noise ratio (S / N) suitable for higher density recording cannot be obtained.
[0064]
On the other hand, when the Cr content exceeds 28 at%, the ratio of Cr not segregating to the grain boundary layer and remaining inside the magnetic particles increases. As a result, the coercive force in the vertical direction and the ratio Mr / Ms between the remanent magnetization (Mr) and the saturation magnetization (Ms) tend to decrease. Furthermore, the crystal orientation of the magnetic particles is impaired, and the ratio (Hc-v) / (Hc-i) of the coercive force (Hc-v) in the vertical direction and the coercive force (Hc-i) in the in-plane direction is small. There is a risk of becoming.
[0065]
If the Pt content is less than 10 at%, the magnetic anisotropy constant (Ku) necessary for the perpendicular magnetic layer cannot be obtained, and the magnetization becomes thermally unstable. If Pt exceeds 20 at%, not only Cr segregation in the magnetic layer is inhibited, but also the fcc structure layer is formed in the magnetic layer, which may cause a decrease in coercive force. Is preferred.
[0066]
If the Nd content is less than 0.5 at%, the effect of increasing the Ku value may be reduced. On the other hand, if Nd is contained in excess of 8 at%, the coercive force is lowered, and as a result, there is a risk of increasing noise during recording and reproduction.
[0067]
B, Ta, and Cu have the effect of promoting Cr segregation in the magnetic layer, reducing the magnetic particle-to-particle interaction and the magnetic particle diameter, and consequently reducing noise during recording and reproduction. The amount of these elements added is preferably 8 at% or less in total for each element. If added in excess of 8 at%, these elements remain in the magnetic particles, and as a result, the perpendicular coercivity and the ratio Mr / Ms of the residual magnetization (Mr) to the saturation magnetization (Ms) are unfavorable.
[0068]
Examples of magnetic materials include Co20Cr14Pt2Nd (Cr content 20at%, Pt content 14at%, Nd content 2at%), Co22Cr12Pt4Nd (Cr content 22at%, Pt content 12at%, Nd content 4at%), Co19Cr14Pt1B1Ta1Nd (Cr content 19at%, Pt content 14at%, B content 1at%, Ta content 1at%, Nd content 1at%), Co22Cr12Pt2B2Nd (Cr content 22at%, Pt content 12at%, B content 2at %, Nd content 2 at%), and CoCrPtNd alloys, CoCrPtBNd alloys, CoCrPtTaNd alloys, CoCrPtCuNd alloys, and CoCrPtBCuNd alloys.
[0069]
The perpendicular magnetic layer 5 may have a single-layer structure made of the above-described magnetic material of the present invention, or may have a multilayer structure laminated in combination with various magnetic materials. When the perpendicular magnetic layer is composed of a plurality of magnetic layers, at least one of them is preferably composed of the perpendicular magnetic layer. In particular, it is preferable that the uppermost layer of the perpendicular magnetic layer contains Nd.
[0070]
In addition to the above, various magnetic materials used for the multilayer structure include CoCrPt alloys, CoCr alloys, CoCrPtB alloys, CoCrPtCu alloys, Co alloys (CoCr, CoB, Co-SiO2 etc.) and Pd alloys ( PdB, Pd—SiO2, etc.), amorphous materials such as TbFeCo, and CoCrPtCu-based materials can also be used.
[0071]
Moreover, when it is set as a multilayer structure, it can also be set as the structure which formed the intermediate | middle layer which consists of nonmagnetic materials between magnetic layers. The nonmagnetic material may be a nonmagnetic metal material having an hcp structure, a nonmagnetic metal material having a bcc structure, an fcc structure, or an amorphous structure, a metal oxide material, or a metal nitride material.
[0072]
The thickness of the perpendicular magnetic layer 5 is preferably 3 to 60 nm (preferably 5 to 40 nm). If the thickness of the perpendicular magnetic layer 5 is less than the above range, sufficient magnetic flux cannot be obtained, and the reproduction output is lowered. On the other hand, if the thickness of the perpendicular magnetic layer 5 exceeds the above range, the magnetic particles in the perpendicular magnetic layer 5 become coarse and the recording / reproducing characteristics are deteriorated.
[0073]
In the perpendicular magnetic layer 5 of the present invention, the ratio Mr / Ms of residual magnetization (Ms) to saturation magnetization (Mr) with respect to the substrate is 0.85 or more (preferably 0.95 or more). A magnetic recording medium having an Mr / Ms of less than 0.85 is not preferable because the reverse domain nucleation magnetic field is lowered and the thermal fluctuation resistance is poor.
[0074]
The perpendicular magnetic layer 5 of the present invention has an activation magnetic moment (vIsb) represented by the product of the activation volume (v) and the saturation magnetic moment (Is) of 0.3 × 10. ^-15 emu ~ 0.8 × 10 ^-15 emu (preferably 0.4 × 10 ^-15 emu ~ 0.7 × 10 ^-15 emu. ). vIsb is 0.3 × 10 ^-15 If it is less than emu, the magnetic cluster size becomes too small and becomes thermally unstable, so that thermal demagnetization easily occurs, which is not preferable as a magnetic recording medium. Also, vIsb is 0.8 × 10 ^-15 Exceeding emu is not preferable because noise during recording and reproduction becomes too large, and a signal / noise ratio (S / N) necessary for high-density recording cannot be obtained.
[0075]
The coercive force (Hc-v) in the perpendicular direction of the magnetic layer is preferably 2500 [Oe] or more. A magnetic recording medium having a coercive force of less than 2500 [Oe] is not suitable for high recording density, and the thermal fluctuation resistance is reduced.
[0076]
The perpendicular magnetic anisotropy (Hc-v) / (Hc-i) represented by the ratio of the coercive force (Hc-v) in the vertical direction to the coercive force (Hc-i) in the in-plane direction is 5 or more. Is preferred. When the value of Hc-v / Hc-i is less than 5, the crystal orientation of the magnetic layer is poor and the C axis, which is the easy axis of Co, is dispersed with respect to the substrate vertical plane. The magnetic force (Hc-v), Mr / Ms ratio, and reverse domain nucleation magnetic field (-Hn) are likely to be lowered. Furthermore, the magnetization is thermally unstable, and not only thermal demagnetization occurs but also noise during recording / reproduction increases, which is not preferable.
[0077]
The reverse magnetic domain nucleation magnetic field (-Hn) of the perpendicular magnetic layer 5 is preferably 0 to 2000 [Oe] (more preferably 0 to 1500 [Oe]). A magnetic recording medium having a reverse domain nucleation magnetic field (-Hn) of less than 0 is not preferable because it is inferior in thermal fluctuation resistance.
[0078]
As shown in FIG. 2, the reverse magnetic domain nucleation magnetic field (-Hn) is a point a, MH where the external magnetic field becomes 0 in the process of decreasing the external magnetic field from the saturation state in the MH curve obtained by VSM or the like. If the intersection point between the saturation magnetization and the line obtained by extending the tangent line of the MH curve at the point b where the magnetization of the curve is 0 is the point c, it can be expressed by the distance [Oe] from the Y axis to the point c.
Note that the reverse domain nucleation magnetic field (-Hn) takes a positive value when the point c is in a region where the external magnetic field is negative (see FIG. 2). Conversely, the point c is positive when the external magnetic field is positive. It takes a negative value when it is in a certain area (see FIG. 3).
[0079]
In this specification, the term “mainly oriented perpendicularly to the substrate” means that the value of the coercive force in the direction perpendicular to the substrate direction measured by, for example, VSM is higher than that in the direction parallel to the substrate. It ’s a big one.
[0080]
The protective layer 6 prevents corrosion of the perpendicular magnetic layer 5 and prevents damage to the surface of the medium when the magnetic head comes into contact with the medium. Conventionally known materials can be used, and include, for example, C, SiO2, and ZrO2. Things can be used.
[0081]
The thickness of the protective layer 6 is preferably 1 to 10 nm from the viewpoint of high recording density because the distance between the head and the medium can be reduced.
[0082]
As the lubricant 7, it is preferable to use perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid or the like.
[0083]
The magnetic recording medium of the present invention comprises, on a nonmagnetic substrate, at least an orientation control layer for controlling the orientation of the layer immediately above, a perpendicular magnetic layer having an easy axis oriented perpendicularly to the substrate, and a protective layer The perpendicular magnetic layer is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, and the ratio of residual magnetization (Mr) and saturation magnetization (Ms) in the direction perpendicular to the substrate Mr / Ms is 0.85 or more, and the activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 Since the magnetic recording medium is characterized by being emu, it is possible to improve the resolution of recording / reproducing characteristics and increase the thermal stability of magnetization without increasing noise during recording / reproducing of the magnetic recording medium. it can.
[0084]
Next, an example of a method for manufacturing the magnetic recording medium having the above configuration will be described.
In order to manufacture the magnetic recording medium having the above-described configuration, the soft magnetic underlayer 2, the orientation control layer 3, the intermediate layer 4, and the perpendicular magnetic layer 5 are sequentially formed on the nonmagnetic substrate 1 by sputtering, vacuum deposition, ion plating. It is formed by a ting method or the like. Next, the protective layer 6 is preferably formed by a plasma CVD method, an ion beam method, or a sputtering method.
[0085]
As the nonmagnetic substrate 1, a metal substrate made of a metal material such as aluminum or an aluminum alloy may be used, or a nonmetal substrate made of a nonmetal material such as glass, ceramic, silicon, silicon carbide, or carbon may be used. Good.
[0086]
As the glass substrate, there are amorphous glass and crystallized glass, and general-purpose soda-lime glass, aluminosilicate glass, and aluminosilicate glass can be used as the amorphous glass. Further, as the crystallized glass, lithium-based crystallized glass can be used. As the ceramic substrate, a sintered body mainly composed of general-purpose aluminum oxide, aluminum nitride, silicon nitride, or the like, or a fiber reinforced material thereof can be used.
[0087]
As the non-magnetic substrate 1, the above-described metal substrate or a non-metal substrate having a NiP layer formed by plating or sputtering may be used.
[0088]
The nonmagnetic substrate preferably has an average surface roughness Ra of 2 nm (20 mm) or less, preferably 1 nm or less, from the viewpoint of suitable for high recording density recording with a low flying head.
[0089]
Further, it is preferable that the micro waviness (Wa) of the surface is 0.3 nm or less (more preferably 0.25 [nm] or less) from the viewpoint of being suitable for high recording density recording with the head flying low. It is preferable for the flight stability of the magnetic head to use one having a chamfered portion of the end face chamfered portion and a surface average roughness Ra of at least one of the side surface portions of 10 nm or less (more preferably 9.5 nm or less). The slight waviness (Wa) can be measured as the surface average roughness in a measuring range of 80 μm using, for example, a surface roughness measuring device P-12 (manufactured by KLM-Tencor).
[0090]
If necessary, the nonmagnetic substrate is cleaned, and the nonmagnetic substrate is placed in the chamber of the film forming apparatus. If necessary, the substrate is heated to 100 to 400 ° C. by a heater, for example. On the nonmagnetic substrate 1, a soft magnetic underlayer 2, an orientation control layer 3, an intermediate layer 4, and a perpendicular magnetic layer 5 are made of DC or RF using a sputtering target made of a material having the same composition as the material of each layer. It is formed by magnetron sputtering. The sputtering conditions for forming the film are as follows, for example. The degree of vacuum is 10 in the chamber used for formation. ^-Four -10 ^-7 Exhaust until Pa is reached. A substrate is housed in a chamber, and sputtering film formation is performed by introducing, for example, Ar gas as a sputtering gas and discharging it. At this time, the supplied power is 0.2 to 2.0 kW, and a desired film thickness can be obtained by adjusting the discharge time and the supplied power.
[0091]
The soft magnetic underlayer 2 is preferably formed to a thickness of 50 to 400 nm by adjusting the discharge time and the power supplied.
[0092]
When forming the soft magnetic underlayer 2, it is preferable to use a sputter target made of a soft magnetic material because the soft magnetic underlayer can be easily formed. As soft magnetic materials, FeCo alloys (FeCo, FeCoV, etc.), FeNi alloys (FeNi, FeNiMo, FeNiCr, FeNiSi, etc.), FeAl alloys (FeAl, FeAlSi, FeAlSiCr, FeAlSiTiRu, FeAlO, etc.), FeCr alloys ( FeCr, FeCrTi, FeCrCu, etc.), FeTa alloys (FeTa, FeTaC, FeTaN, etc.), FeMg alloys (FeMgO, etc.), FeZr alloys (FeZrN, etc.), FeC alloys, FeN alloys, FeSi alloys, FeP alloys Examples include alloys, FeNb alloys, FeHf alloys, FeB alloys, and FeAlO, FeMgO, FeTaN, and FeZrN containing 60 at% or more of Fe. Furthermore, CoZr, CoZrNb, CoZrTa, CoZrCr, CoZrMo-based alloys containing Co at 80 at% or more, containing at least one of Zr, Nb, Ta, Cr, Mo, etc. and having an amorphous structure are suitable. Can be cited as
[0093]
The target is an alloy target or a sintered alloy target obtained by a melting method.
[0094]
It is preferable to include a step of oxidizing the surface after the soft magnetic underlayer 2 is formed. For example, after forming the soft magnetic underlayer 2, a method of exposing to an atmosphere containing oxygen, or a method of introducing oxygen during a process when forming a portion close to the surface of the soft magnetic underlayer 2 can be given.
[0095]
After forming the soft magnetic underlayer 2, the orientation control layer 3 is formed to a thickness of 0.5 to 40 nm (preferably 1 to 20 nm) by adjusting the discharge time and the power supplied. Examples of the sputtering target material used to form the orientation control layer include Ru-based alloys, Ni-based alloys, and Co-based alloys.
[0096]
After forming the orientation control layer, a magnetic layer having a film thickness of 15 to 40 nm is similarly formed by sputtering using a sputtering target made of the material of the magnetic layer. As materials for the sputtering target, Co20Cr14Pt2Nd (Cr content 20 at%, Pt content 14 at%, Nd content 2 at%), Co22Cr12Pt4Nd (Cr content 22 at%, Pt content 12 at%, Nd content 4 at%), Co19Cr14Pt1B1Ta1Nd (Cr content 19at%, Pt content 14at%, B content 1at%, Ta content 1at%, Nd content 1at%), Co22Cr12Pt2B2Nd (Cr content 22at%, Pt content 12at%, B content 2at %, Nd content 2at%), CoCrPtNd alloy, CoCrPtBNd alloy, CoCrPtTaNd alloy, CoCrPtCuNd alloy, CoCrPtBCuNd alloy
CoCrPt alloy, CoCr alloy, CoCrPtB alloy, CoCrPtCu alloy, Co alloy (CoCr, CoB, Co—SiO 2 etc.) and Pd alloy (PdB, Pd—SiO 2 etc.) laminated material or TbFeCo etc. An amorphous material and a CoCrPtCu-based material can be mentioned.
[0097]
It is also preferable to use an element other than Cr, Pt, and Nd to which one or more elements selected from B, Ta, and Cu are added.
[0098]
The ratio Mr / Ms between the residual magnetization (Mr) and the saturation magnetization (Ms) in the direction perpendicular to the substrate is 0.85 or more, made of a material containing Co as a main component and containing at least Cr, Pt, and Nd. The activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 The sputtering conditions for forming the perpendicular magnetic layer, which is emu, are as follows, for example.
[0099]
A target made of a material containing Co as a main component and containing at least Cr, Pt, and Nd is used. ^-Four -10 ^-7 In a state where the air is exhausted to Pa, the substrate is accommodated in the chamber, and, for example, Ar gas is introduced as a sputtering gas and discharged to perform sputtering film formation. At this time, the supplied power is 0.2 to 2.0 kW, and a desired film thickness can be obtained by adjusting the discharge time and the supplied power.
[0100]
The pressure of the sputtering gas is preferably 3 to 20 Pa (more preferably 5 to 15 Pa).
[0101]
When an intermediate layer is provided between the nonmagnetic underlayer and the magnetic layer, it is preferable to use a sputtering target made of a CoCr alloy (Cr content is 25 to 45 at%). The CoCr alloy includes a CoCr alloy, a CoCrX1 alloy, a CoX1 alloy (X1: Pt, Ta, Zr, Ru, Nb, Cu, Re, Ni, Mn, Ge, Si, O, N, and B or one or two selected Species or more). At this time, when the magnetic layer contains B, the film is formed under sputtering conditions such that the Cr concentration in the region where the B concentration is 1 at% or more is 40 at% or less near the boundary between the nonmagnetic underlayer and the magnetic layer. It is preferable to do this.
[0102]
After forming the magnetic layer, a protective film such as a protective film mainly composed of carbon is formed using a known method such as sputtering, plasma CVD or a combination thereof.
[0103]
Further, a lubricating layer is formed on the protective film by applying a perfluoropolyether fluorine-based lubricant by dipping or spin coating as necessary.
[0104]
In the magnetic recording medium manufactured according to the present invention, the perpendicular magnetic layer is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, and the remanent magnetization (Mr) and the saturation magnetization in the direction perpendicular to the substrate. The ratio Mr / Ms to (Ms) is 0.85 or more, and the activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 Since the magnetic recording medium is characterized by being emu, it is possible to improve the resolution of recording / reproducing characteristics and increase the thermal stability of magnetization without increasing noise during recording / reproducing of the magnetic recording medium. it can.
[0105]
Further, in the manufacturing method of the present invention using the above-described sputter target, the perpendicular magnetic layer is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd. The ratio Mr / Ms between Mr) and the saturation magnetization (Ms) is 0.85 or more, and the activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 A magnetic recording medium characterized by being emu can be easily manufactured.
[0106]
FIG. 5 shows an example of a magnetic recording / reproducing apparatus using the magnetic recording medium. The magnetic recording / reproducing apparatus shown here includes a magnetic recording medium 50 having the structure shown in FIG. 1, a medium driving unit 51 that rotationally drives the magnetic recording medium 50, a magnetic head 52 that records and reproduces information on the magnetic recording medium 50, and A head driving unit 53 that moves the magnetic head 52 relative to the magnetic recording medium 50 and a recording / reproducing signal processing system 54 are provided. The recording / reproducing signal processing system 54 can process data input from the outside and send the recording signal to the magnetic head 52, or can process the reproducing signal from the magnetic head 52 and send the data to the outside. ing. As the magnetic head 52 used in the magnetic recording / reproducing apparatus of the present invention, a head suitable for higher recording density having a GMR element utilizing a giant magnetoresistive effect (GMR) as a reproducing element can be used.
According to the magnetic recording / reproducing apparatus, the perpendicular magnetic layer is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, and has a remanent magnetization (Mr) and a saturation magnetization (Mr) perpendicular to the substrate. Ms) is 0.85 or more, and the activation magnetic moment represented by the product of the activation volume and the saturation magnetic moment is 0.3 × 10 ^-15 emu ~ 0.8 × 10 ^-15 Since a magnetic recording medium characterized by emu is used, the resolution of recording / reproducing characteristics is improved and the thermal stability of magnetization is increased without increasing noise during recording / reproducing of the magnetic recording medium. Therefore, a magnetic recording / reproducing apparatus suitable for high recording density is obtained.
[0107]
FIG. 4 shows a second embodiment of the magnetic recording medium of the present invention, in which the hard magnetic anisotropy mainly faces the in-plane direction between the nonmagnetic substrate 1 and the soft magnetic underlayer 2. A magnetic layer 8 can be provided.
[0108]
The hard magnetic layer 8 includes a CoSm alloy or a CoCrPtX2 alloy (X2: one or more of Pt, Ta, Zr, Nb, Cu, Re, Ni, Mn, Ge, Si, O, N, and B). Is preferably used.
[0109]
The hard magnetic layer 8 preferably has a coercive force Hc of 500 [Oe] or more (preferably 1000 [Oe] or more).
[0110]
The thickness of the hard magnetic layer 8 is preferably 150 nm or less (preferably 70 nm or less). If the thickness of the hard magnetic layer 8 exceeds 150 nm, the surface average roughness Ra of the orientation control layer 3 is increased, which is not preferable.
[0111]
The hard magnetic layer 8 is preferably exchange-coupled with the soft magnetic underlayer 2 so that the magnetization direction of the hard magnetic layer is the substrate radial direction. As a result, since the magnetization of the soft magnetic layer 2 is fixed in the radial direction by exchange coupling, the write magnetic field by the head and the direction of magnetization are orthogonal, and the exchange coupling state becomes more stable during recording and reproduction. As a result, generation of noise can be suppressed, which is preferable.
[0112]
By providing the hard magnetic layer 8, it is possible to more effectively suppress the formation of huge magnetic domains in the soft magnetic underlayer 2, thereby preventing the occurrence of spike noise due to the domain wall and reducing the error rate during recording and reproduction. It can be made low enough.
[0113]
In order to control the orientation of the hard magnetic layer 8, a Cr alloy material or a B2 structural material may be used between the nonmagnetic substrate 1 and the hard magnetic layer 8.
[0114]
In order to manufacture the magnetic recording medium having the above configuration, the process of forming the hard magnetic layer 8 on the substrate 1 is included, and then the soft magnetic underlayer 2 is formed by sputtering or the like, and then the soft magnetic underlayer 2 is formed as necessary. The surface of the magnetic underlayer 2 is oxidized, then the orientation control layer 3, the intermediate film 4, and the perpendicular magnetic layer 5 are formed by sputtering or the like, and then the protective layer 6 is formed by CVD, ion beam, sputtering, or the like. Form. Next, the lubricating layer 7 is formed by a dipping method, a spin coating method, or the like.
[0115]
For example, in order to form the hard magnetic layer, a conventional method of creating an in-plane isotropic medium can be used. For example, the structure of glass substrate / NiAl alloy layer / CrMo alloy layer / CoCr alloy layer / CoCrPtB alloy layer can be mentioned. Next, a magnetic field in the radial direction is applied to the magnetic recording medium formed up to the protective film to impart radial magnetization to the hard magnetic layer. The strength of the applied magnetic field is preferably a magnetic field at which the hard magnetic layer is sufficiently magnetically saturated, for example, 790000 A / m (10000 [Oe]) or more.
[0116]
【Example】
Hereinafter, an example is shown and the operation effect of the present invention is clarified. However, the present invention is not limited to the following examples.
Example 1
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the film forming chamber until reaching Pa, a target of 89Co4Zr7Nb (Co content 89 at%, Zr content 4 at%, Nb content 7 at%) is used on the glass substrate at a substrate temperature of 100 ° C. or lower. A soft magnetic underlayer 2 having a thickness of 100 nm was formed by sputtering. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). .
[0117]
Next, the substrate is heated to 200 ° C., and an orientation control layer 3 having a thickness of 20 nm is formed on the soft magnetic underlayer using a Ru target. 65Co30Cr5B (Co content 65 at%, Cr content 30 at%, (B content 5 at%) Target film 5 nm thick intermediate film 4, 68Co18Cr10Pt4Nd (Co content 68 at%, Cr content 18 at%, Pt content 10 at%, Nd content 4 at%) Target film thickness A 20 nm perpendicular magnetic layer 5 was sequentially formed. Note that in the sputtering step, argon was used as a sputtering gas for film formation, and the film was formed at a pressure of 0.6 Pa.
Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium.
(Examples 2 to 11)
A magnetic recording medium was produced in the same manner as in Example 1 except that the composition and thickness of the perpendicular magnetic layer 5 were changed.
[0118]
(Comparative Example 1)
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the deposition chamber until reaching Pa, a soft magnetic underlayer 2 having a thickness of 100 nm was formed on the glass substrate by sputtering using a 89Co4Zr7Nb target at a substrate temperature of 100 ° C. or lower. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). .
Next, the substrate is heated to 200 ° C., an orientation control layer 3 having a thickness of 20 nm is formed on the soft magnetic underlayer using a Ru target, and an intermediate film 4 and 72Co18Cr10Pt having a thickness of 5 nm using a 65Co30Cr5B target. A 20 nm perpendicular magnetic layer 5 was sequentially formed using a target. Note that in the sputtering step, argon was used as a sputtering gas for film formation, and the film was formed at a pressure of 0.6 Pa. Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium.
[0119]
(Comparative Examples 2 to 12)
A magnetic recording medium was manufactured in the same manner as in Comparative Example 1 except that the composition and thickness of the perpendicular magnetic layer 5 were changed.
[0120]
The magnetic characteristics of the magnetic recording media of Examples 1 to 11 and Comparative Examples 1 to 12 were measured with a vibration type magnetic characteristic measuring device (VSM). The ratio (Hc-v) / (Hc-i) of the coercive force (Hc-v) in the vertical direction and the coercive force (Hc-i) in the in-plane direction was evaluated as follows. A sample without a soft magnetic underlayer is separately prepared, and (Hc-v) is a direction parallel to the substrate surface, so that a magnetic field is applied in a direction perpendicular to the substrate surface. The ratio was calculated by measuring the magnetic field applied in the circumferential direction or radial direction.
[0121]
Further, the evaluation result of vIsb was calculated from the above-described equation by measuring time-dependent data of the coercive force in the vertical direction using a vibration type magnetic property measuring apparatus.
[0122]
The recording / reproducing characteristics were measured using a read / write analyzer RWA1632 manufactured by GUZIK and a spin stand S1701MP. For the evaluation of the electromagnetic conversion characteristics, a composite thin film magnetic recording head having a giant magnetoresistive (GMR) element in the reproducing section was used, and the recording conditions were measured at a linear recording density of 500 kFCI.
[0123]
Regarding thermal fluctuation resistance (thermal demagnetization), after writing at 70 ° C. with a linear recording density of 50 kFCI using a spin stand S1701MP, the rate of decrease in output relative to the playback output 1 second after writing (% / decade) ) Was calculated based on (So-S) × 100 / (So × 3). In this equation, So represents the reproduction output when 1 second has elapsed after signal recording on the magnetic recording medium, and S represents the reproduction output after 1000 seconds. The results are shown in Table 2.
[0124]
(Example 12)
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the deposition chamber until reaching Pa, a soft magnetic underlayer 2 having a thickness of 100 nm was formed on the glass substrate by sputtering using a 89Co4Zr7Nb target at a substrate temperature of 100 ° C. or lower. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). .
Next, the substrate is heated to 200 ° C., the orientation control layer 3 having a thickness of 20 nm is formed on the soft magnetic underlayer using a Ru target, and the intermediate film 4 and 58Co22Cr14Pt2B4Nd having a thickness of 5 nm using a 65Co30Cr5B target. A perpendicular magnetic layer 5 having a thickness of 20 nm was sequentially formed using a target. In the sputtering step, argon was used as a sputtering gas for film formation, and the film was formed at a pressure of 0.6 Pa.
Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium.
[0125]
(Examples 13 to 16)
A magnetic recording medium was prepared in the same manner as in Example 12 except that the composition of the perpendicular magnetic layer 5 was changed.
[0126]
(Comparative Examples 13 and 14)
A magnetic recording medium was prepared in the same manner as in Comparative Example 1 except that the composition of the perpendicular magnetic layer 5 was changed. The magnetic properties (Hc-v) / (Hc-i) and vIsb of the magnetic recording media of Examples 12 to 16 and Comparative Examples 13 and 14 were measured and evaluated in the same manner as in Example 1.
The results are shown in Table 3.
[0127]
(Example 17)
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the deposition chamber until reaching Pa, a soft magnetic underlayer 2 having a thickness of 100 nm was formed on the glass substrate by sputtering using a 89Co4Zr7Nb target at a substrate temperature of 100 ° C. or lower. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). .
Next, the surface was exposed to oxygen gas. The exposure was carried out using a 50% oxygen-argon mixed gas as the exposure gas and leaving it at a pressure of 1 Pa for 10 seconds.
Next, the substrate was heated to 200 ° C., the orientation control layer 3 having a thickness of 20 nm was formed on the soft magnetic underlayer using a Ru target, and the intermediate film 4 having a thickness of 5 nm was formed using a 65Co30Cr5B target. . Further, 63Co18Cr14Pt having a film thickness of 15 nm was formed as the first perpendicular magnetic layer 51, and a film thickness of 5 nm was sequentially formed as the second perpendicular magnetic layer 52 using a 59Co22Cr14Pt5Nd target. In the sputtering step, argon was used as a sputtering gas for film formation, and the film was formed at a pressure of 0.6 Pa.
Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium.
[0128]
(Examples 18 and 19)
A magnetic recording medium was produced in the same manner as in Example 17 except that the first perpendicular magnetic layer 51 was changed as shown in Table 4.
The magnetic properties (Hc-v) / (Hc-i) and vIsb of the magnetic recording media of Examples 17, 18, and 19 were measured and evaluated in the same manner as in Example 1.
The results are shown in Table 4.
[0129]
(Example 20)
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the film forming chamber until Pa is reached, a film of 94Cr6Mo for controlling the orientation of the hard magnetic layer 8 is formed on the glass substrate to a thickness of 20 nm, and Co20Cr14Pt4B is formed as the hard magnetic layer 8 to a thickness of 50 nm. Formed. Next, a soft magnetic underlayer 2 having a thickness of 100 nm was formed by sputtering using a 89Co4Zr7Nb target at a substrate temperature of 100 ° C. or lower. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). .
Next, the surface was exposed to oxygen gas. The exposure was carried out using a 50% oxygen-argon mixed gas as the exposure gas and left in an atmosphere of 1 Pa for 10 seconds.
Next, the substrate is heated to 200 ° C., the orientation control layer 3 having a thickness of 20 nm is formed on the soft magnetic underlayer using a Ru target, the intermediate film 4 having a thickness of 5 nm using a 65Co30Cr5B target, and a 59Co22Cr14Pt5Nd target. The perpendicular magnetic layer 5 having a thickness of 20 nm was sequentially formed using Note that in the sputtering step, argon was used as a sputtering gas for film formation, and the film was formed at a pressure of 0.6 Pa. Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium. The obtained magnetic recording medium was applied with a voltage of 200 V to a magnetizing jig dedicated to a magnetic recording medium for generating a pulse magnetic field having a reciprocal width on the order of 10 msec, and 948 kA / m (11850 [Oe]) in the radial direction. A strong pulse magnetic field was applied to fix the magnetization in the radial direction.
[0130]
(Examples 21 to 24)
A magnetic recording medium was prepared in the same manner as in Example 20 except that the composition and thickness of the hard magnetic layer were changed. The magnetic properties (Hc-v) / (Hc-i) and vIsb of the magnetic recording media of Examples 20 to 24 were measured and evaluated in the same manner as in Example 1.
The results are shown in Table 5.
[0131]
(Example 25)
A cleaned glass substrate (made by OHARA, outer diameter 2.5 inches) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3010 made by Anelva), and the ultimate vacuum is 1 × 10. ^-Five After evacuating the deposition chamber until reaching Pa, a soft magnetic underlayer 2 having a thickness of 100 nm was formed on the glass substrate by sputtering using a 89Co4Zr7Nb target at a substrate temperature of 100 ° C. or lower. It was confirmed by a vibration type magnetic property measuring apparatus (VSM) that the product Bs · t (T · nm) of the saturation magnetic flux density Bs (T) and the film thickness t (nm) of this film was 120 (T · nm). . Next, the substrate is heated to 200 ° C., and an orientation control layer 3 having a thickness of 20 nm is formed on the soft magnetic underlayer using a Ru target. A perpendicular magnetic layer 5 having a thickness of 20 nm was sequentially formed using a target. In the sputtering process for forming the perpendicular magnetic layer 5, the film was formed at a pressure of 3 Pa using argon as a sputtering gas for film formation. In other sputtering processes for film formation, the film was formed at 0.6 Pa. Next, a protective layer 6 having a thickness of 5 nm was formed by a CVD method. Next, a lubricating layer 7 made of perfluoropolyether was formed by a dipping method to obtain a magnetic recording medium.
[0132]
(Examples 26 to 28)
A magnetic recording medium was produced in the same manner as in Example 24 except that the deposition pressure of the perpendicular magnetic layer 5 was changed. The magnetic properties (Hc-v) / (Hc-i) and vIsb of the magnetic recording media of Examples 25 to 28 were measured and evaluated in the same manner as in Example 1.
The results are shown in Table 6.
[0133]
[Table 2]

[0134]
From Table 2, by using a magnetic material in which Nd is added to the perpendicular magnetic layer 5, the increase in vIsb is suppressed, and the Mr / Ms ratio, (Hc-v) / (Hc-i), and -Hn are improved. It can be seen that the resolution, S / N ratio, and thermal fluctuation characteristics during recording and reproduction are improved. In Example 1, the Mr / Ms ratio, (Hc-v) / (Hc-i), and -Hn are improved by adding Nd as compared with Comparative Example 1 in which Nd is not added. Further, in Comparative Examples 1 to 5 in which Pt was increased in order to obtain a magnetic characteristic equivalent to that of Example 1, it was necessary to add Pt to 20 at%, and vIsb increased due to an increase in the amount of Pt. It can be seen that the S / N ratio at the time of recording and reproduction decreases. On the other hand, from Examples 7 to 9, by increasing the Nd content, the Mr / Ms ratio, (Hc-v) / (Hc-i), and -Hn are further improved without substantially increasing vIsb. You can see that From this, it can be seen that it is more effective to add Nd than to increase Pt in improving the magnetic characteristics of the magnetic recording medium. From Comparative Examples 6 to 8, when the Cr content is out of the range of 18 to 28 at%, when the amount of Nd added exceeds 8 at%, the Mr / Ms ratio and the thermal fluctuation resistance are reduced, or vIsb is increased. In addition, it can be seen that the S / N ratio at the time of recording and reproduction decreases. From Comparative Example 9, when the amount of Pt is less than 10 at%, the effect of adding Nd is hardly obtained. Further, it can be seen from Comparative Example 10 that when the Pt amount exceeds 20 at%, the magnetic characteristics are rapidly deteriorated.
[0135]
[Table 3]

[0136]
The magnetic characteristics can be controlled by adding Nd to the magnetic material forming the perpendicular magnetic layer 5 and further adding Cu, B, and Ta. However, as seen in Comparative Examples 9 and 10, it can be seen that when the total content of Cu, B, and Ta exceeds 8 at%, the magnetic properties deteriorate.
[0137]
[Table 4]

[0138]
It can be seen that the magnetic characteristics are improved by providing a plurality of perpendicular magnetic layers 5 and using one of them as a magnetic material to which Nd is added.
[0139]
[Table 5]

[0140]
It can be seen that various materials can be used as the hard magnetic layer 8.
[0141]
[Table 6]

[0142]
It can be seen that by increasing the sputtering gas pressure during the formation of the perpendicular magnetic layer 5, vIsb can be further reduced without impairing other characteristics. From Example 28, it can be seen that when the film forming pressure exceeds 20 Pa, the magnetic properties deteriorate.
[0143]
【The invention's effect】
As described above, in the magnetic recording medium of the present invention, the perpendicular magnetic layer is formed of a material containing Co as a main component and containing at least Cr, Pt, and Nd, without impairing recording / reproducing characteristics. , Magnetic properties can be improved. Furthermore, since the magnetic characteristics can be improved by controlling the Nd content instead of Pt, the Pt content in the perpendicular magnetic layer can be reduced, and an increase in the manufacturing cost of the magnetic recording medium can be prevented. it can.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of a magnetic recording medium of the present invention.
FIG. 2 is a diagram showing an example of a magnetization curve.
FIG. 3 is a diagram showing another example of a magnetization curve.
FIG. 4 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 5 is a schematic configuration diagram showing an example of a magnetic recording / reproducing apparatus using the magnetic recording medium of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic board | substrate, 2 ... Soft magnetic underlayer, 3 ... Orientation control layer, 4 ... Intermediate | middle layer, 5 ... Perpendicular magnetic layer, 6 ... Protective layer, 7 ... Lubrication layer, 8 ... Hard magnetic layer
50: magnetic recording medium, 51: medium driving unit, 52: magnetic head, 53: head driving unit, 54: recording / reproducing signal processing system

Claims (13)

On the non-magnetic substrate, at least an orientation control layer for controlling the orientation of the layer immediately above, a perpendicular magnetic layer having an easy axis oriented perpendicularly to the substrate, and a protective layer are provided. Is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd. The perpendicular magnetic layer has a Cr content of 18 to 28 at%, a Pt content of 10 to 20 at%, and an Nd content of 0.1. 5 to 8 at%, the ratio (Mr / Ms) of remanent magnetization (Mr) and saturation magnetization (Ms) in the direction perpendicular to the substrate is 0.85 or more, and the product of the activation volume and the saturation magnetic moment the magnetic recording medium, characterized in that in represented by activation magnetic moment is ^{0.3 × 10 -15 emu~0.8 × 10 -15} emu. The coercive force in the vertical direction with respect to the substrate is 2500 [Oe] or more, and the ratio (Hc-v) of the coercive force (Hc-v) in the vertical direction to the coercive force (Hc-i) in the plane parallel to the substrate. 2. The magnetic recording medium according to claim 1, wherein: / (Hc-i) is 5 or more. 3. The magnetic recording medium according to claim 1, wherein a reverse domain nucleation magnetic field in a direction perpendicular to the substrate is 0 to 2000 [Oe]. Perpendicular magnetic layer, B, Ta, include any one or more selected from Cu, any one of claims 1 to 3 the total content of these elements, characterized in that it consists of the material is less than 8at% 1 The magnetic recording medium according to Item. 5. A magnetic recording medium, wherein the perpendicular magnetic layer comprises a plurality of magnetic layers, at least one of which comprises the perpendicular magnetic layer according to any one of claims 1 to 4 . 6. A magnetic recording medium, wherein the uppermost magnetic layer of the perpendicular magnetic layers composed of a plurality of magnetic layers comprises the perpendicular magnetic layer according to any one of claims 1 to 5 . The magnetic recording medium according to any one of claims 1 to 6, characterized in that the soft magnetic underlayer of a soft magnetic material is provided between the nonmagnetic substrate and the alignment control layer. The magnetic recording medium according to any one of claims 1 to 7 the surface of the soft magnetic layer is characterized in that it is oxidized or nitrided. 9. The magnetic recording medium according to claim 7, wherein a hard magnetic layer having a magnetic anisotropy mainly in an in-plane direction is provided between the nonmagnetic substrate and the soft magnetic underlayer. The hard magnetic layer is a CoSm alloy or a CoCrPtX2 alloy (X2: one or more of Pt, Ta, Zr, Nb, Cu, Re, Ni, Mn, Ge, Si, O, N, and B). The magnetic recording medium according to claim 9 , wherein the magnetic recording medium is made of a material including, has a coercive force of 500 [Oe] or more, and a magnetization direction is a substrate radial direction. On the nonmagnetic substrate, at least an orientation control layer for controlling the orientation of the layer immediately above, a perpendicular magnetic layer with an easy axis oriented perpendicularly to the substrate, and a protective layer are sequentially formed. In the method of manufacturing a perpendicular magnetic recording medium including the steps, in the step of forming the perpendicular magnetic layer by a sputtering method, it is made of a material containing Co as a main component and containing at least Cr, Pt, and Nd, and a Cr content of 18 A method for producing a magnetic recording medium, comprising using a sputtering target having a content of ˜28 at%, a Pt content of 10 to 20 at%, and an Nd content of 0.5 to 8 at%. 12. The method of manufacturing a magnetic recording medium according to claim 11 , wherein the pressure of the sputtering gas in the step of forming the perpendicular magnetic layer is 3 to 20 Pa. Before the step of forming the orientation control layer, after the soft magnetic layer is formed and the soft magnetic layer is formed, the surface is selected from oxygen gas, nitrogen gas, a mixed gas thereof, or a gas containing them. The method of manufacturing a magnetic recording medium according to claim 11 , further comprising a step of exposing to any of the gases.

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