JP2005038495A - Perpendicular magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium having high recording density and excellent recording and reproducing characteristics and to provide a method of manufacturing the same. <P>SOLUTION: The recording medium has a magnetic layer 6 of a multilayered lamination structure composed of laminated cobalt layers to be first magnetic layers 6a and platinum layers (or palladium layers) to be second magnetic layers 6b. At least one element selected from the group consisting of Ru, Ta, Nb, Mo, Mn, Cr, Si, and Ni, or an oxide is added to at least one of the cobalt layers and the platinum layers (or the palladium layers) in a concentration ranging from 1 to 15 mol %. The magnetic layer 6 is formed on an underlayer 5 of a ruthenium film or the like provided for reducing magnetic interaction between the magnetic particles in the magnetic layer 6. The surface of the underlayer 5 is subjected to oxygen adsorption treatment prior to film deposition of the magnetic layer 6 to suppress magnetic interaction between the magnetic particles in the magnetic layer 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２５】
この表に示すように、Ａｒガスに比較して、ＫｒガスやＸｅガスを用いてスパッタ成膜した磁性層６を備える媒体は高い結晶磁気異方性を示すことがわかる。
表２は、磁気力顕微鏡（ＭＦＭ）を用いて測定した、各媒体の磁性層６の磁気クラスタサイズを纏めた結果であり、磁気クラスタサイズが小さいほど高記録密度に有利になる。
【００２６】
【表２】

【００２７】
この表から分るように、Ａｒガスに比べてＫｒガスやＸｅガスをスパッタガスとして用いることで磁気クラスタサイズを小さくすることができ、記録密度の向上に有利である。すなわち、磁性層６の成膜に際しては、ＫｒガスやＸｅガスをスパッタガスとして用いることにより、垂直磁気記録媒体の磁気特性の向上を図ることが可能となる。
以上説明した結果をもとに、スパッタガスとしてＫｒガスを選び、Ｃｏ層に上述した種々の元素を添加させて記録再生特性の向上を図ることとした。
図５は、磁性層６の成膜時のスパッタガス中に酸素ガスを添加する効果を説明するための図で、磁性層を構成するＣｏ層に、Ｎｉ、Ｔａ、Ｎｂ、Ｍｏ、Ｍｎ、Ｃｒ、Ｓｉの各元素を添加するとともに、スパッタガスであるＫｒガスに質量流量比０〜０．２％の酸素ガスを添加してスパッタを行って作製した垂直磁気記録媒体の保磁力の酸素添加量依存性で、この図において、縦軸が保磁力、横軸が酸素添加量である。
【００２８】
保磁力の酸素添加量依存性は添加元素の種類によって異なるものの、酸素添加により保磁力が向上することが確認される。これは、添加元素が雰囲気中の酸素により酸化されて酸化物を形成してＣｏ粒子間に析出する結果、Ｃｏ粒子相互間の磁気的相互作用が低減されたものと考えられ、この事実は後述する記録再生特性の向上にも寄与し得るものである。
図６は、Ｃｏ層に５ａｔ％Ｎｉを添加した層（９５ａｔ％Ｃｏ−５ａｔ％Ｎｉ層）をＰｔ層と多層積層させた磁性層を備える垂直磁気記録媒体（媒体Ａ）、および、９５ａｔ％Ｃｏ−５ａｔ％Ｎｉ層にＳｉＯ_２を１０ｍｏｌ％添加した層（９０ｍｏｌ％（９５ａｔ％Ｃｏ−５ａｔ％Ｎｉ）−１０ｍｏｌ％ＳｉＯ_２）をＰｔ層と多層積層した磁性層を備える垂直磁気記録媒体（媒体Ｂ）の記録再生特性（ＳＮ特性）を説明するための図で、この図の縦軸はＳＮ比（ＳＮＲ）、横軸は線記録密度である。また、比較のため、純Ｃｏ層とＰｔ層を多層積層した磁性層を備える垂直磁気記録媒体（媒体Ｃ）の記録再生特性（ＳＮ特性）も同時に示している。なお、これらの媒体の磁性層はすべて、Ｋｒガスに質量流量比０．２％の酸素ガスを添加してスパッタ成膜したものであり、記録再生特性の評価は面内媒体用のリングヘッドを用いて実行した。
【００２９】
媒体Ｃでは４００ｋＦＣＩ程度の記録密度までしか記録再生できないが、媒体Ａでは媒体Ｃに比べて２００ｋＦＣＩ以上の領域でＳＮＲが顕著に向上しており、５５０ｋＦＣＩまでは充分に記録再生が行えることが確認された。また、媒体Ｂでは媒体ＡよりもさらにＳＮＲが改善されている。このように、Ｃｏ層にＮｉやＳｉＯ_２などの金属や酸化物を添加することで記録再生特性が向上し、記録密度の向上に効果的であることが確認された。
（実施例２）
本実施例では、磁性層６をＣｏＲｕ／Ｐｔ多層積層構造とし、裏打ち層２としてＣｏＺｒＮｂ膜を用いた垂直磁気記録媒体を作製した。
この垂直磁気記録媒体の製造方法は以下のとおりである。基板１は厚み１ｍｍで直径３．５インチのガラス基板としたが、その径や厚さは本質的ではなく、基板１としてＮｉ−Ｐメッキされ適切なテクスチャーが形成されたＡｌ基板などでもよい。
【００３０】
基板１を充分に洗浄したのちに、ＣｏＺｒＮｂ膜を成膜して裏打ち層２をスパッタリング法により形成する。本実施例で用いたスパッタターゲットは、８７ａｔ％Ｃｏ−５ａｔ％Ｚｒ−８ａｔ％Ｎｂの組成である。スパッタガスとしてＡｒガスを用い、Ａｒガス圧約１Ｐａで室温にて約２００ｎｍの厚さに成膜した。なお、ＣｏＺｒＮｂ膜は、室温成膜した非晶質状態でも充分な軟磁気特性を有する。
このＣｏＺｒＮｂ膜の上に連続して、Ｐｔの下地層５をスパッタ成膜する。用いたターゲットは純Ｐｔである。Ｋｒガスに質量流量比４％のＡｒガスおよび質量流量比０．２％のＯ_２ガスを混合させた混合ガスでスパッタを行い、膜厚約１０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約５Ｐａである。
【００３１】
次に、このＰｔの下地層５の上に、ＣｏＲｕ／Ｐｔ多層積層膜からなる磁性層６をスパッタリングにより形成する。用いたターゲット組成は、Ｃｏ層について９５ａｔ％Ｃｏ−５ａｔ％Ｒｕ、Ｐｔ層について純Ｐｔであり、これらのターゲットを同時に放電してスパッタさせながら回転することでＣｏＲｕ層とＰｔ層とを交互に積層させる。Ｋｒガスに質量流量比４％のＡｒガスと質量流量比０．２％のＯ_２ガスを混合した混合ガスでスパッタを行い、膜厚はＣｏＲｕ層が０．４５ｎｍ、Ｐｔ層が０．８ｎｍである。なお、この成膜は室温で行っており、ガス圧は５Ｐａである。
最後に、磁性層６の最表面に保護層７としてカーボン膜をスパッタリング法により形成する。ターゲットをカーボン、スパッタガスをＡｒガスとし、膜厚約７ｎｍで成膜した。なお、成膜温度は室温、Ａｒガス圧は約１Ｐａである。
【００３２】
図７は、Ｃｏ層に５ａｔ％のＲｕを添加した層（９５ａｔ％Ｃｏ−５ａｔ％Ｒｕ層）をＰｔ層と多層積層させた磁性層を備える垂直磁気記録媒体（媒体Ｄ）、および、９５ａｔ％Ｃｏ−５ａｔ％Ｒｕ層にＯ_２を０．２ｍｏｌ％添加した層（９９．８ｍｏｌ％（９５ａｔ％Ｃｏ−５ａｔ％Ｒｕ）−０．２ｍｏｌ％Ｏ_２）層）をＰｔ層と多層積層させた磁性層を備える垂直磁気記録媒体（媒体Ｅ）の記録再生特性（ＳＮ特性）を説明するための図で、この図の縦軸はＳＮＲ、横軸は線記録密度である。また、比較のため、純Ｃｏ層とＰｔ層を多層積層させた磁性層を備える垂直磁気記録媒体（媒体Ｆ）の記録再生特性（ＳＮ特性）も同時に示している。なお、これらの媒体の磁性層はすべて、Ｋｒガスに質量流量比０〜０．２％の酸素ガスを添加してスパッタ成膜したものであり、記録再生特性の評価は面内媒体用のリングヘッドを用いて実行した。
【００３３】
媒体Ｆでは５００ｋＦＣＩ程度の記録密度までしか記録再生できていないが、媒体Ｄでは媒体Ｆに比べてＳＮＲが向上しており、５００ｋＦＣＩまでは充分に記録再生が行えることが確認された。また、媒体Ｅでは媒体ＤよりもさらにＳＮＲが改善されている。
このように、Ｃｏ層にＲｕを添加すること、または、同時にＯ_２を添加することで記録再生特性が向上し、記録密度の向上に効果的であることが確認された。
（実施例３）
本実施例の垂直磁気記録媒体は、図１に示したとおり、Ａｌなどの非磁性の基板１上に、軟磁性の裏打ち層２と、第１の配向制御層３と、第２の配向制御層４と、下地層５と、多層積層構造の磁性層６と、カーボンの保護層７とが順次積層されて構成されている。
【００３４】
磁性層６として第１の磁性層６ａであるＣｏ‐ＳｉＯ_２層と第２の磁性層６ｂであるＰｔ層とを交互に多層積層されたＣｏ‐ＳｉＯ_２／Ｐｔを用いることとし、ＣｏにＳｉＯ_２を添加することでＣｏ粒子間に非磁性のＳｉＯ_２を偏析させてＣｏ粒子の微細化・孤立化を図っている。このＣｏ‐ＳｉＯ_２層中のＳｉＯ_２添加量は、好ましくは２〜１５ｍｏｌ％、更に好ましくは５〜１１ｍｏｌ％と設定される。
また、下地層５として、表面に酸素吸着させたＲｕ下地層を用いることにより、Ｈｃ付近での磁化曲線の傾きを緩やかにして垂直磁性層の粒子間の磁気的相互作用を小さくし、記録再生を容易化している。
さらに、Ｒｕの下地層５の結晶をｃ軸配向させて保磁力を向上させることを目的として、結晶配向制御用に第１の配向制御層３としてＴａ層、第２の配向制御層４としてＮｉＦｅＣｒ層を用いる。この場合のＮｉＦｅＣｒ層の組成は、ＮｉＦｅＣｒ層上に設けられるＲｕの下地層５の結晶性向上と結晶配向制御性を低下させない範囲で適宜選択され、例えば、５０〜７０ａｔ％Ｎｉ−１０〜２０ａｔ％Ｆｅ−２０〜３０ａｔ％Ｃｒの範囲で設定される。
【００３５】
また、各層の厚みは、好ましくは、第１の配向制御層３の膜厚は１〜１０ｎｍ、第２の配向制御層４の膜厚は５〜１５ｎｍ、下地層５の膜厚は１０〜２０ｎｍ、Ｃｏ‐ＳｉＯ_２層の膜厚は０．２〜０．８ｎｍ、そして、Ｐｔ層の膜厚は０．１〜１ｎｍの範囲で設定される。
これらの層に加え、非磁性の基板１と第１の配向制御層３との間に軟磁性のＣｏＺｒＴａの裏打ち層２を膜厚５０〜４００ｎｍの範囲で設けることで記録ヘッドでの書込能力を増大させることを可能としている。
以下に、上記構成の垂直磁気記録媒体の製造方法について説明する。用いる非磁性の基板は３．５インチ径の厚み１ｍｍのＡｌ基板であるがその径や厚さは本質的ではなく、基板としてガラス基板を用いてもよい。
【００３６】
基板を充分に洗浄したのちに、軟磁性のＣｏＺｒＴａをスパッタ成膜して裏打ち層とする。ここで用いたターゲットは９２ａｔ％Ｃｏ‐５ａｔ％Ｚｒ‐３ａｔ％Ｔａの組成である。スパッタガスとしてＡｒガスを用い、約１Ｐａのガス圧下で室温にて約２００ｎｍの厚さに成膜した。なお、ＣｏＺｒＴａは室温成膜した非晶質状態でも充分な軟磁気特性を有する。
このＣｏＺｒＴａ膜の上に、連続して、Ｔａの第１の配向制御層３をスパッタ成膜する。用いたターゲットは純Ｔａである。Ａｒガスでスパッタを行い膜厚約５ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。
このＴａ膜の上に、連続して、ＮｉＦｅＣｒの第２の配向制御層４をスパッタ成膜する。用いたターゲットの組成は６０ａｔ％Ｎｉ−１５ａｔ％Ｆｅ−２５ａｔ％Ｃｒである。Ａｒガスでスパッタを行い膜厚約１０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。
【００３７】
このＮｉＦｅＣｒ膜の上に、下地層５であるＲｕ膜をスパッタ成膜する。用いたターゲットは純Ｒｕである。Ａｒガスでスパッタを行い膜厚約２０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約４Ｐａである。このようにして成膜したＲｕ下地層の表面を、０．１〜１０Ｐａの圧力下でＡｒガスに質量流量比１〜１０％のＯ_２ガスを混合させた雰囲気中に１〜２０秒程度曝してＲｕ表面に適度な量の酸素を吸着させた。
次に、このＲｕの下地層５の上に、Ｃｏ−ＳｉＯ_２／Ｐｔ多層積層膜からなる垂直配向した磁性層６をスパッタリングにより形成する。用いたターゲットは、Ｃｏに９ｍｏｌ％のＳｉＯ_２を添加させた組成（９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２）のターゲット、および、純Ｐｔである。これらの２つのターゲットを同時に放電してスパッタさせながら回転させることで、Ｃｏ−ＳｉＯ_２層とＰｔ層とを交互に積層させる。なお、成膜されたＣｏ−ＳｉＯ_２層の組成は、用いたターゲットの組成を反映して９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２である。Ａｒガスでスパッタを行い、膜厚はＣｏ−ＳｉＯ_２層が０．３ｎｍ、Ｐｔ層が０．１ｎｍである。なお、この成膜は室温で行っており、ガス圧は５Ｐａである。
【００３８】
最後に、磁性層６の最表面に保護層７として窒素ドープのカーボン（Ｃ：Ｎ）膜をスパッタリング法により膜厚約７ｎｍで成膜した。なお、成膜温度は室温、Ａｒガス圧は約１Ｐａである。
図８は、本発明の垂直磁気記録媒体が備える結晶配向制御層の効果を説明するための図で、第１および第２の配向制御層であるＴａ層およびＮｉＦｅＣｒ層を順次成膜した上にＲｕの下地層５を成膜し、さらにＣｏ−ＳｉＯ_２／Ｐｔ多層積層構造の磁性層６を成膜した試料から得られたＸ線回折パターンである。この図から、Ｒｕの下地層５からは（００２）面からのみの回折が認められ、配向制御層（３および４）がＲｕの下地層５をｃ軸配向させるのに有効に作用していることが分る。
【００３９】
図９は、Ｒｕの下地層５表面に酸素を吸着させる効果を説明するための図で、上述した方法で作製された本発明の垂直磁気記録媒体・ＢＲ＞ゥら得られた磁化曲線である。横軸の単位はＯｅ、縦軸の単位はｅｍｕである。この図において、保磁力Ｈｃ付近の磁化曲線の傾きは小さく、磁性層を構成する磁性粒間の磁気的相互作用が小さくなっていることを示している。すなわち、Ｒｕ下地層５の表面に酸素を吸着させることにより、記録再生が容易化されるという効果を奏する。
表３は、本実施例のＣｏ‐ＳｉＯ_２／Ｐｔ磁性層を備える媒体の保磁力（Ｈｃ）、角形比（Ｓ）、飽和磁化（Ｍｓ）、逆磁区核形成磁界（Ｈｎ）、磁化曲線の傾き（α）を、Ｃｏにボロン（Ｂ）を添加したＣｏ−Ｂ層とＰｔ層を積層したＣｏ−Ｂ／Ｐｔ磁性層（従来品）を備える媒体の保磁力と比較した結果を纏めたものである。なお、Ｃｏ−Ｂ／Ｐｔ磁性層の下地層としてはＰｔ層を用いた。
【００４０】
【表３】

【００４１】
Ｃｏ‐ＳｉＯ_２／Ｐｔ磁性層の保磁力は、Ｃｏ−Ｂ／Ｐｔ磁性層の保磁力に比較して１０００Ｏｅ以上高く、また、磁化曲線の傾き（α）も８．５から１．８へと大きく低下している。すなわち、Ｒｕ下地層５の上にＣｏ‐ＳｉＯ_２層とＰｔ層とを交互に多層積層させることで、高い保磁力と緩やかな磁化曲線の傾きとを同時に可能とする垂直磁気記録媒体を得ることができる。
表４は、これらの２つの垂直磁気記録媒体の結晶磁気異方性を評価した結果を纏めたもので、結晶磁気異方性定数（Ｋｕ）が大きいほど媒体の熱安定性が高いことを意味する。
【００４２】
【表４】

【００４３】
この表から分るように、Ｃｏ‐ＳｉＯ_２／Ｐｔ磁性層のＫｕは、Ｃｏ−Ｂ／Ｐｔ磁性層のＫｕに比較して僅かながらではあるが高く、熱安定性が向上していることが分る。このように、本発明の垂直磁気記録媒体は、従来の垂直磁気記録媒体に比較して優れた磁気特性を示すことが理解できる。
図１０は、従来品と上記本発明品の各々の記録再生特性である再生出力を説明するための図で、このグラフの横軸は線記録密度であり、縦軸はＴＡＡ（Ｔｒａｃｋ Ａｖｅｒａｇｅ Ａｍｐｌｉｔｕｄｅ）である。この評価には、面内媒体用のリングヘッドを用いている。Ｐｔ下地層の上にＣｏ−Ｂ層とＰｔ層とを積層させた従来品では、４００ｋＦＣＩ程度の記録密度までしか再生できていないのに対して、Ｒｕ下地層の上にＣｏ−ＳｉＯ_２層とＰｔ層とを積層させた磁性層を備える媒体では、５４０ｋＦＣＩ以上でも再生信号が検出されており、高い線記録密度まで再生可能なことが分る。
【００４４】
図１１は、従来品と上記本発明品の記録再生特性である媒体ノイズを説明するための図で、このグラフの横軸は線記録密度であり、縦軸はノイズである。この評価にも面内媒体用のリングヘッドを用いている。Ｐｔ下地層の上にＣｏ−Ｂ層とＰｔ層とを積層させた従来品では、２００ｋＦＣＩ以上になるとノイズ出力が低下しており、充分な記録再生が行われていないことを示しておりノイズ自体も大きい。これに対して、Ｒｕ下地層の上にＣｏ−ＳｉＯ_２層とＰｔ層とを積層させた本発明品では、すべての線記録密度で従来品より低ノイズであることに加え、５４０ｋＦＣＩまでノイズの増加が確認できており充分な記録再生特性が得られている。
図１２は、従来品と上記本発明品の記録再生特性であるＳＮＲを説明するための図で、このグラフの横軸は線記録密度であり、縦軸はＳＮＲである。この評価にも面内媒体用のリングヘッドを用いている。Ｃｏ−Ｂ層とＰｔ層とを積層させた従来品に比較して、Ｃｏ−ＳｉＯ_２層とＰｔ層とを積層させた本発明品では、すべての線記録密度で圧倒的に高いＳＮＲを示し５４０ｋＦＣＩまで記録再生が充分に行われている。
【００４５】
このように、本発明の垂直磁気記録媒体の構成は記録再生特性の向上に効果的であり、記録密度の向上にも寄与することが分る。
（実施例４）
本実施例の垂直磁気記録媒体は、基板１としてＡｌ基板を用い、この上にＣｏＺｒＮｂ軟磁性の裏打ち層２と２層構造の配向制御層（３および４）とＲｕの下地層５を順次積層し、さらに、Ｃｏ‐ＳｉＯ_２層とＰｔ層とを多数積層させた磁性層６が設けられている。なお、本実施例の配向制御層は第１の層としてＴａ層３を用い、第２の層としてはＮｉＦｅＮｂＢ層４を用いている。また、ここで用いたＡｌ基板は３．５インチ径で厚みが１ｍｍであるが、その径や厚さは本質的ではなく、Ａｌ基板にかえてガラス基板を用いてもよい。
【００４６】
以下にこの垂直磁気記録媒体の製造プロセスについて説明する。
基板を充分に洗浄したのちに、軟磁性のＣｏＺｒＮｂをスパッタ成膜して裏打層２とする。ここで用いたターゲットは８７ａｔ％Ｃｏ‐５ａｔ％Ｚｒ‐８ａｔ％Ｎｂの組成である。スパッタガスとしてＡｒガスを用い、約１Ｐａのガス圧下で室温にて約２００ｎｍの厚さに成膜した。なお、ＣｏＺｒＮｂは室温成膜した非晶質状態でも充分な軟磁気特性を有する。
このＣｏＺｒＮｂ軟磁性膜の上に、連続して、第１の配向制御層３であるＴａ層をスパッタ成膜する。用いたターゲットは純Ｔａである。Ａｒガスでスパッタを行い、膜厚約５ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。
【００４７】
このＴａ膜の上に連続して、第２の配向制御層４であるＮｉＦｅＮｂＢ層をスパッタ成膜する。用いたターゲットは７９ａｔ％Ｎｉ−１２ａｔ％Ｆｅ−３ａｔ％Ｎｂ−６ａｔ％Ｂの組成である。Ａｒガスでスパッタを行い、膜厚約３０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。
このＮｉＦｅＮｂＢ層の上に、下地層５であるＲｕ膜をスパッタ成膜する。用いたターゲットは純Ｒｕである。Ａｒガスでスパッタを行い、膜厚約２０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約４Ｐａである。このようにして成膜したＲｕの下地層５の表面を、１Ｐａの圧力下で、Ａｒガスに質量流量比２％のＯ_２ガスを混合した雰囲気に１０秒程度曝してＲｕ表面に適度な量の酸素を吸着させる。
【００４８】
次に、このＲｕの下地層５の上に、Ｃｏ−ＳｉＯ_２／Ｐｔ多層積層膜からなる垂直配向した磁性層６をスパッタリングにより形成する。用いたターゲットは、Ｃｏ−ＳｉＯ_２層成膜用として９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２の組成もしくは９４ｍｏｌ％Ｃｏ−６ｍｏｌ％ＳｉＯ_２の組成、Ｐｔ層成膜用として純Ｐｔのターゲットである。これら２つのターゲットを同時に放電してスパッタさせながら回転させることで、Ｃｏ−ＳｉＯ_２層とＰｔ層とを交互に積層する。Ａｒガスでスパッタを行い、膜厚はＣｏ−ＳｉＯ_２層が０．３ｎｍ、Ｐｔ層が０．１ｎｍである。なお、この成膜は室温で行っており、ガス圧は５Ｐａである。このようにして得られるＣｏ−ＳｉＯ_２層の組成はターゲットの組成を反映して、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２または９４ｍｏｌ％Ｃｏ−６ｍｏｌ％ＳｉＯ_２である。
【００４９】
最後に、磁性層６の最表面に保護層７として窒素ドープのカーボン（Ｃ：Ｎ）膜をスパッタリング法により形成する。ターゲットをカーボンとし、スパッタガスをＡｒガスに質量流量比４％のＮ_２ガスを混合させた混合ガスとし、膜厚約７ｎｍで成膜した。なお、成膜温度は室温、Ａｒガス圧は約１Ｐａである。
図１３は、磁性層６を構成するＣｏ−ＳｉＯ_２層内での磁性粒子径と非磁性の粒界幅の様子を説明するための平面ＴＥＭ像であり、図１３（ａ）はＳｉＯ_２添加量が６ｍｏｌ％の試料、図１３（ｂ）はＳｉＯ_２添加量が９ｍｏｌ％の試料である。このＴＥＭ像を解析すると、ＳｉＯ_２添加量が６ｍｏｌ％の試料（図１３（ａ））では平均磁性粒子径７．１ｎｍ、平均粒界幅１．５ｎｍであるのに対し、ＳｉＯ_２添加量が９ｍｏｌ％の試料（図１３（ｂ））では平均磁性粒子径５．６ｎｍ、平均粒界幅１．６ｎｍであることがわかる。すなわち、添加ＳｉＯ_２量が多いほど、磁性粒子の平均粒径が小さく、かつ、平均粒界幅が大きくなる傾向があることがわかる。一般に、磁性結晶粒径が小さくなると粒子同士の磁気的相互作用が弱まり、個々の磁性粒の孤立化の程度が高くなり、高記録密度を目指すうえで適している。
【００５０】
図１４は、第２の磁性層６ｂであるＰｔ層の膜厚を変化させた場合の磁気特性の変化を説明するための図で、図１４（ａ）は保磁力Ｈｃ、図１４（ｂ）は磁化曲線の傾きαの、Ｐｔ膜厚依存性である。Ｐｔ膜厚がゼロ（Ｐｔ膜を設けない場合）はＨｃがゼロであるのに対し、膜厚０．１２ｎｍで約６０００ＯｅのＨｃ値を示す。Ｈｃの値はＰｔ膜厚０．２５ｎｍで約１２００Ｏｅまで低下し、さらに膜厚の増大に伴ってＨｃ値は徐々に低下する。一方、α値は、Ｐｔ膜厚０．１２ｎｍでα＝１．５を示し、Ｐｔ膜厚が厚くなると増加する傾向を示す。このように、Ｐｔ層の膜厚は薄い方が望ましく、本実施例の場合には０．１２ｎｍが最適である。
図１５は、ＮｉＦｅＮｂＢ層４の膜厚を変化させた場合の磁気特性の変化を説明するための図で、図１５（ａ）は記録再生特性の４００ｋＦＣＩでのノイズであり、図１５（ｂ）は同じく４００ｋＦＣＩでのＳＮＲである。なお、比較のために、ＮｉＦｅＮｂＢ層の代わりに膜厚１０ｎｍのＮｉＦｅＣｒ層を設けた場合の磁気特性も示してある。
【００５１】
図１５（ａ）に示すように、ＮｉＦｅＮｂＢの膜厚を１０ｎｍから３０ｎｍに厚くするに従いノイズが低減する傾向を示し、ＮｉＦｅＮｂＢ膜厚を３０ｎｍにすると膜厚１０ｎｍのＮｉＦｅＣｒ層を設けた場合よりもノイズレベルが低くなる。また、図１５（ｂ）に示すように、ＮｉＦｅＮｂＢ膜を設けた場合のＳＮＲ値は、その膜厚に関わらず、膜厚１０ｎｍのＮｉＦｅＣｒ膜を用いた場合よりも高い値となっている。
このように、Ｃｏ層へのＳｉＯ_２添加量を制御することで磁性粒径や非磁性粒界層の幅を制御でき、Ｐｔ層の膜厚を最適化することで高いＨｃが得られ、さらに、Ｒｕ層の直下に設けられることとなる層を実施例３のＮｉＦｅＣｒ層から１０〜３０ｎｍのＮｉＦｅＮｂＢ層とすることでノイズおよびＳＮＲを改善することができる。このようにして、さらに高い記録密度を達成可能な垂直磁気記録媒体を作製可能となる。
（実施例５）
本実施例の垂直磁気記録媒体は、実施例４で説明した媒体と略同じ構成の媒体であるが、Ｒｕの下地層５の上に設けられる磁性層６をＣｏ−ＳｉＯ_２／Ｐｄ多層積層構造としている点が異なる。磁性層６の成膜に用いたターゲット組成は、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２組成ものと純Ｐｄのものであり、これらのターゲットを同時に放電してスパッタさせながら回転させることで、Ｃｏ−ＳｉＯ_２層とＰｄ層とを交互に積層させる。Ａｒガスでスパッタを行い、膜厚はＣｏ−ＳｉＯ_２層が０．３ｎｍ、Ｐｄ層が０．７２ｎｍである。なお、この成膜は室温で行っており、ガス圧は５Ｐａである。
【００５２】
図１６は、第２の磁性層６ｂであるＰｄ層の膜厚を変化させた場合の磁気特性の変化を説明するための図で、図１６（ａ）は保磁力Ｈｃ、図１６（ｂ）は磁化曲線の傾きαの、Ｐｄ膜厚依存性である。Ｐｄ膜が厚くなるのに伴ってＨｃ値が高くなり、Ｐｄ膜厚０．７２ｎｍでほぼ一定の値（約５５００Ｏｅ）に落ち着く。一方、α値はＰｄ膜厚に殆ど依存せず、２前後の値を示しており、磁性粒子相互間の磁気的相互作用は充分に小さいことを示している。
図１７は、Ｃｏ‐ＳｉＯ_２／Ｐｄ多層積層構造の磁性層６の磁気特性に及ぼすＲｕ下地層５の効果について説明するための図で、図１７（ａ）は記録再生特性のノイズであり、図１７（ｂ）はＳＮＲである。なお、比較のため、下地層としてＰｔ膜およびＰｄ膜を用いた場合についても示している。図１７（ａ）に示すように、Ｐｔ膜やＰｄ膜を下地層として用いた場合にはノイズが大きく、かつ、高い線記録密度では充分な記録再生が行えていないが、下地層としてＲｕ膜を用いた場合にはノイズも小さく、かつ、高い線記録密度まで充分な記録再生がなされていることがわかる。また、図１７（ｂ）に示したＳＮＲ値も、Ｒｕ膜を用いた場合に格段に良好な結果が得られている。
【００５３】
図１８は、実施例４で説明した本発明のＣｏ‐ＳｉＯ_２／Ｐｔ多層積層構造の磁性層を備える垂直磁気記録媒体と、本実施例５のＣｏ‐ＳｉＯ_２／Ｐｄ多層積層構造の磁性層を備える垂直磁気記録媒体との記録再生特性を説明するための図で、図１８（ａ）は再生出力（ＴＡＡ）特性、図１８（ｂ）はノイズ特性、図１８（ｃ）はＳＮＲ特性である。再生出力およびノイズともにＣｏ‐ＳｉＯ_２／Ｐｄ多層積層構造の磁性層を備える垂直磁気記録媒体の方が小さいが、ＳＮＲはＣｏＳｉＯ_２／Ｐｔ多層積層構造の磁性層を備える垂直磁気記録媒体とほぼ同等である。このように、磁性層としてＣｏＳｉＯ_２／Ｐｄ多層積層構造を採用しても、Ｒｕ膜を下地層として設けることで、優れた垂直磁気記録媒体が作製可能である。
（実施例６）
本実施例では、基板１をＡｌ基板、裏打ち層２をＣｏＺｒＮｂ膜、Ｔａ層３とＮｉＦｅＣｒ層４の２層構造の配向制御層、下地層５をＲｕ膜、磁性層６をＣｏ−ＳｉＯ_２組成のＣｏ層とＰｔ−ＳｉＯ_２組成のＰｔ層とを多層積層させて構成した例について説明する。なお保護層７にはカーボン膜を用いている。
【００５４】
この垂直磁気記録媒体の製造方法は、以下のとおりである。基板１は厚み１ｍｍで直径３．５インチのＡｌ基板であるが、その径や厚さは本質的ではなく、ガラス基板でもよい。
基板１を充分に洗浄したのちに、ＣｏＺｒＮｂ膜を成膜して裏打ち層２をスパッタリング法により形成する。本実施例で用いたスパッタターゲットは、８７ａｔ％Ｃｏ‐５ａｔ％Ｚｒ‐８ａｔ％Ｎｂの組成である。スパッタガスとしてＡｒガスを用い、Ａｒガス圧約１Ｐａで、室温にて、約２００ｎｍの厚さに成膜した。なお、ＣｏＺｒＮｂ膜は、室温成膜した非晶質状態でも充分な軟磁気特性を有する。
このＣｏＺｒＮｂ膜の上に、連続して、第１の配向制御層３であるＴａ層をスパッタ成膜する。用いたターゲットは純Ｔａである。Ａｒガスでスパッタを行い、膜厚約３ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。このＴａ層の上に連続して、第２の配向制御層４であるＮｉＦｅＣｒ層をスパッタ成膜する。用いたターゲットは６０ａｔ％Ｎｉ−１５ａｔ％Ｆｅ−２５ａｔ％Ｃｒの組成である。Ａｒガスでスパッタを行い、膜厚約１０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約１Ｐａである。これらのＴａ層とＮｉＦｅＣｒ層の２層で配向制御層を構成し、この上に成膜される下地層５たるＲｕ膜をｃ軸配向させる。
【００５５】
ＮｉＦｅＣｒ層上にＲｕ膜をスパッタ成膜して下地層５とする。用いたターゲットは純Ｒｕである。Ａｒガスでスパッタを行い膜厚約２０ｎｍの厚さに成膜した。成膜温度は室温、ガス圧は約４Ｐａである。このようにして成膜した下地層５の表面を、１Ｐａの圧力下でＡｒガスに質量流量比２％のＯ_２ガスを混合させた混合ガス雰囲気に１０秒程度曝してＲｕ膜の表面に適度な量の酸素を吸着させる。下地層５の表面に酸素を吸着させることにより、磁性層６のＨｃ付近での磁化曲線の傾きを緩やかにして磁性層を構成する磁性粒相互間の磁気的相互作用を低減させている。
次に、このＲｕ膜の下地層５の上に、Ｃｏ−ＳｉＯ_２／Ｐｔ−ＳｉＯ_２多層積層膜からなる垂直配向した磁性層をスパッタリングにより形成する。成膜に用いたターゲットは各々、９１〜９４ｍｏｌ％Ｃｏ−６〜９ｍｏｌ％ＳｉＯ_２および９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２の組成の２つのターゲットであり、これらのターゲットを同時に放電してスパッタさせながら回転させることで、Ｃｏ−ＳｉＯ_２層とＰｔ−ＳｉＯ_２層とを交互に積層させる。Ａｒガスでスパッタを行い、膜厚はＣｏ−ＳｉＯ_２層が０．３ｎｍ、Ｐｔ−ＳｉＯ_２層が０．０７〜０．２５ｎｍである。なお、この成膜は室温で行っており、ガス圧は５Ｐａである。
【００５６】
最後に、磁性層６の最表面に保護層７として窒素ドープのカーボン（Ｃ：Ｎ）膜をスパッタリング法により形成する。ターゲットをカーボン、スパッタガスをＡｒガスに質量流量比４％のＮ_２ガスを混合させた混合ガスとし、膜厚約７ｎｍで成膜した。なお、成膜温度は室温、Ａｒガス圧は約１Ｐａである。
図１９は、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層、および、９４ｍｏｌ％Ｃｏ−６ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層、ならびに、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える垂直磁気記録媒体の各々のＨｃの、第２の磁性層６ｂの膜厚に対する依存性を説明するための図である。第１の磁性層であるＣｏ層へのＳｉＯ_２の添加量が９ｍｏｌ％の場合、Ｐｔ層へＳｉＯ_２を５ｍｏｌ％添加した媒体のＨｃはＳｉＯ_２無添加の媒体に比較して３００〜５００Ｏｅ程度低い値を示すが、Ｃｏ層へのＳｉＯ_２添加量を６ｍｏｌ％とした媒体は極めて高いＨｃを示すことがわかる。
【００５７】
図２０は、上記３種の垂直磁気記録媒体の各々の磁化曲線のＨｃ付近の傾きαの、第２の磁性層６ｂの膜厚に対する依存性を説明するための図である。何れの媒体においてもα値を最小とする最適な第２の磁性層の膜厚が存在することが読み取れる。また、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層を備える媒体と、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える媒体とを比較すると、Ｐｔ層にＳｉＯ_２を添加した媒体では何れの第２の磁性層膜厚においても０．１５〜０．４程度低いα値を示している。αは磁性粒相互間の磁気的相互作用の大きさの目安であることを考慮すると、Ｐｔ層にＳｉＯ_２を添加したことにより磁性粒同士の磁気的相互作用の程度が低くなり、ノイズが低減されることを意味している。
【００５８】
図２１は、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層を備える媒体と、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える垂直磁気記録媒体の、各々の磁気異方性定数Ｋｕの、第２の磁性層６ｂの膜厚に対する依存性を説明するための図である。何れの媒体においても略同じＫｕ値を示しており、Ｐｔ層中へのＳｉＯ_２の添加によるＫｕの低下はないことを意味している。
図２２は、ＨｃのＣｏ層中ＳｉＯ_２添加量依存性を調べるために、Ｃｏ層に１８〜３８体積％のＳｉＯ_２を添加したＣｏ−ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える媒体を作製し、各々の媒体のＨｃを測定した結果を纏めたものである。以下、ｍｏｌ％と体積％の換算は次の式で行なっている。
【００５９】
Ｃｏ中のＳｉＯ_２の体積％は、［（ＳｉＯ_２のｍｏｌ％／１００）＊ＳｉＯ_２１モルでの体積＊１００］／［（ＳｉＯ_２のｍｏｌ％／１００）＊ＳｉＯ_２１モルでの体積＋｛１−（ＳｉＯ_２のｍｏｌ％／１００）｝＊Ｃｏ１モルでの体積］。Ｐｔ中のＳｉＯ_２の体積％は、［（ＳｉＯ_２のｍｏｌ％／１００）＊ＳｉＯ_２１モルでの体積＊１００］／［（ＳｉＯ_２のｍｏｌ％／１００）＊ＳｉＯ_２１モルでの体積＋｛１−（ＳｉＯ_２のｍｏｌ％／１００）｝＊Ｐｔ１モルでの体積］。ここで、ＳｉＯ_２、Ｃｏ、Ｐｔの１モルでの体積（ｃｍ^３）はそれぞれ、２３．１１、６．５８、９．０９とした。
図２２に示すように、媒体のＨｃは、Ｃｏ層へのＳｉＯ_２添加量の増大に伴って急激に低下する。このことは、磁性粒同士の粒界にＳｉＯ_２を多く偏析させて個々の磁性粒の孤立性を高めてノイズを低減しようとすると、高いＨｃは得られなくなることを意味している。
【００６０】
図２３は、ＨｃのＰｔ層中へのＳｉＯ_２添加効果を説明するための図で、Ｃｏ層に１８〜３８体積％のＳｉＯ_２を添加するとともにＰｔ層中にもＳｉＯ_２を添加し、Ｃｏ−ＳｉＯ_２／Ｐｔ−ＳｉＯ_２多層積層膜磁性層を備える媒体を作製し、これらの媒体のＨｃを、Ｐｔ層中にはＳｉＯ_２の添加のないＣｏ−ＳｉＯ_２／Ｐｔ多層積層膜磁性層を備える媒体のＨｃと比較した結果を纏めたものである。
既に図２２を用いて説明したように、Ｐｔ層にＳｉＯ_２を添加せず、Ｃｏ層にのみＳｉＯ_２を添加した媒体の場合には、Ｃｏ層中へのＳｉＯ_２添加量が増加するとＨｃは急激に低下するが、Ｃｏ層へのＳｉＯ_２添加に加えＰｔ層にもＳｉＯ_２を添加すると、Ｈｃの減少傾向は緩和されることがわかる。すなわち、Ｃｏ層のみならずＰｔ層中へもＳｉＯ_２添加することとすれば、同じＨｃを与える媒体においてより多くのＳｉＯ_２添加が可能となる。その結果、磁性粒同士の粒界にＳｉＯ_２を多く偏析させて個々の磁性粒の孤立性を高めてノイズを低減させやすくなる。
【００６１】
【発明の効果】
以上説明したように、本発明の垂直磁気記録媒体は、その磁性層をＣｏ層とＰｔ層（またはＰｄ層）とを多層に積層させた多層積層膜で基本構成し、かつ、これらＣｏ層とＰｔ層（またはＰｄ層）の双方もしくは何れか一方にＳｉなどの元素の酸化物を添加し、かかる構成の磁性層を、磁性層を構成する磁性粒相互間の磁気的相互作用を小さくするために設けられたＲｕ膜などの下地層上に形成するようにした。また、磁性層の成膜に先立って下地層の表面に酸素吸着処理を施して、磁性層の磁性粒間の磁気的相互作用を抑制するようにした。これにより、高記録密度で記録再生特性に優れる垂直磁気記録媒体を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明の垂直磁気記録媒体の構成例を説明するための図である。
【図２】純Ｃｏ層と純Ｐｔ層とを、Ａｒ、Ｋｒ、または、Ｘｅガスをスパッタガスとして多層積層させた膜の、Ｐｔ層膜厚と保磁力との関係を示す図である。
【図３】純Ｃｏ層と純Ｐｔ層とを、Ａｒ、Ｋｒ、または、Ｘｅガスをスパッタガスとして多層積層させた膜の、磁化曲線のＨｃ付近の傾きのＰｔ層膜厚依存性を説明するための図である。
【図４】純Ｃｏ層と純Ｐｔ層とを、Ａｒ、Ｋｒ、または、Ｘｅガスをスパッタガスとして多層積層させた膜の、保磁力Ｈｃのスパッタガス圧依存性を説明するための図である。
【図５】磁性層成膜時のスパッタガス中に酸素ガスを添加する効果を説明するための図である。
【図６】９５ａｔ％Ｃｏ−５ａｔ％Ｎｉ層とＰｔ層を多層積層させた磁性層を備える垂直磁気記録媒体（ＣｏＮｉ／Ｐｔ媒体）、および、｛９０ｍｏｌ％（９５ａｔ％Ｃｏ−５ａｔ％Ｎｉ）−１０ｍｏｌ％ＳｉＯ_２｝層とＰｔ層を多層積層させた磁性層を備える垂直磁気記録媒体（ＣｏＮｉ−ＳｉＯ_２／Ｐｔ媒体）の記録再生特性（ＳＮ特性）を説明するための図である。
【図７】９５ａｔ％Ｃｏ−５％Ｒｕ層とＰｔ層を多層積層させた磁性層を備える垂直磁気記録媒体（ＣｏＲｕ／Ｐｔ媒体）、および、｛９９．８ｍｏｌ％（９５ａｔ％Ｃｏ−５ａｔ％Ｒｕ）−０．２ｍｏｌ％Ｏ_２｝層とＰｔ層を多層積層させた磁性層を備える垂直磁気記録媒体（ＣｏＲｕＯ_２／Ｐｔ媒体）の記録再生特性（ＳＮ特性）を説明するための図である。
【図８】本発明の垂直磁気記録媒体が備える結晶配向制御層の効果を説明するための図である。
【図９】下地層の表面に酸素を吸着させる効果を説明するための図である。
【図１０】従来品と本発明品の記録再生特性である再生出力を説明するための図である。
【図１１】従来品と本発明品の記録再生特性である媒体ノイズを説明するための図である。
【図１２】従来品と本発明品の記録再生特性であるＳＮＲを説明するための図である。
【図１３】磁性層を構成するＣｏ−ＳｉＯ_２層内での磁性粒子径と非磁性の粒界幅の様子を説明するための平面ＴＥＭ像である。
【図１４】Ｐｔ層の膜厚を変化させた場合の磁気特性の変化を説明するための図である。
【図１５】ＮｉＦｅＮｂＢ層の膜厚を変化させた場合の磁気特性の変化を説明するための図である。
【図１６】Ｐｄ層の膜厚を変化させた場合の磁気特性の変化を説明するための図である。
【図１７】Ｃｏ‐ＳｉＯ_２／Ｐｄ多層積層構造の磁性層の磁気特性に及ぼすＲｕ下地層の効果について説明するための図である。
【図１８】実施例４で説明した本発明のＣｏ‐ＳｉＯ_２／Ｐｔ多層積層構造の磁性層を備える垂直磁気記録媒体と、実施例５のＣｏ‐ＳｉＯ_２／Ｐｄ多層積層構造の磁性層を備える垂直磁気記録媒体との記録再生特性を説明するための図である。
【図１９】９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層、および、９４ｍｏｌ％Ｃｏ−６ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層、ならびに、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える垂直磁気記録媒体の各々のＨｃの、第２の磁性層の膜厚に対する依存性を説明するための図である。
【図２０】図１９で説明した３種の垂直磁気記録媒体の各々の磁化曲線のＨｃ付近の傾きαの、第２の磁性層の膜厚に対する依存性を説明するための図である。
【図２１】９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／９５ｍｏｌ％Ｐｔ−５ｍｏｌ％ＳｉＯ_２多層積層膜からなる磁性層を備える媒体と、９１ｍｏｌ％Ｃｏ−９ｍｏｌ％ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える垂直磁気記録媒体各々の、磁気異方性定数Ｋｕの第２の磁性層の膜厚に対する依存性を説明するための図である。
【図２２】Ｃｏ層に１８〜３８体積％のＳｉＯ_２を添加しＣｏ−ＳｉＯ_２／Ｐｔ多層積層膜からなる磁性層を備える媒体のＨｃを測定した結果を纏めた図である。
【図２３】ＨｃのＰｔ層中へのＳｉＯ_２添加効果を説明するための図である。
【符号の説明】
１ 基板
２ 裏打ち層
３ 第１の配向制御層
４ 第２の配向制御層
５ 下地層
６ 磁性層
６ａ 第１の磁性層
６ｂ 第２の磁性層
７ 保護層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a perpendicular magnetic recording medium and a manufacturing method thereof, and more particularly to a perpendicular magnetic recording medium having a high recording density and excellent recording / reproducing characteristics and a manufacturing method thereof.
[0002]
[Prior art]
In recent personal computers and workstations, a large-capacity and small-sized magnetic recording device is mounted as a storage device. Against this background, magnetic disks are required to have higher recording density.
The magnetic recording system currently in practical use is the “in-plane (longitudinal) magnetic recording system” in which the easy axis of magnetization is parallel to the surface of the magnetic recording medium. In order to improve the recording density in this in-plane magnetic recording method, it is necessary to reduce the product of the residual magnetization (Br) and the magnetic layer thickness (t) of the magnetic film included in the recording medium. It is also necessary to increase the magnetic force (Hc). For this reason, attempts have been made to control the crystal grain size by reducing the thickness of the magnetic film.
[0003]
However, in the in-plane magnetic recording system, there is a problem that the demagnetizing field increases with the shortening of the bit length and the residual magnetic flux density decreases, so that the reproduction output decreases. There is also a “thermal fluctuation problem” that becomes apparent as the film becomes thinner. For these reasons, it is currently expected that it will be technically difficult to increase the density of the magnetic disk by the in-plane magnetic recording method.
On the other hand, a “perpendicular magnetic recording method” has been studied in order to improve the surface recording density while solving these problems. In the perpendicular magnetic recording system, the magnetic recording medium is designed so that the easy axis of magnetization of the magnetic film is oriented in the direction perpendicular to the substrate surface, so that adjacent magnetizations in the magnetization transition region do not face each other, and the bit length Is suitable as a magnetic recording method for a high-density magnetic recording medium because the magnetization is stable even when the magnetic field becomes shorter and the magnetic flux does not decrease.
[0004]
On the other hand, the perpendicular magnetic recording medium does not sufficiently segregate nonmagnetic materials into the region between the magnetic grains in the magnetic layer, resulting in a large magnetic interaction between the magnetic grains. There is a problem that medium noise tends to be high. Therefore, it is required to achieve high-density recording while reducing medium noise and improving the S / N ratio by developing a material control technique that can promote grain boundary segregation of nonmagnetic substances.
As a configuration of a known perpendicular magnetic recording medium for this purpose, for example, a soft magnetic backing layer is formed on a nonmagnetic substrate such as aluminum or glass, and an underlayer for orienting the magnetic layer vertically is formed thereon. A “two-layer perpendicular magnetic recording medium” is known in which a perpendicular magnetic recording layer and a protective layer are further formed thereon (see, for example, Patent Document 1). Perpendicular magnetization films made of Co-based alloys such as Cr, Co-Cr-Ta, Co-Cr-Pt, multilayer laminated perpendicular magnetization films such as Pt / Co and Pd / Co, Tb-Co, Tb-Fe-Co, etc. Many film configurations such as an amorphous perpendicular magnetization film have been studied. Among them, a multilayer laminated perpendicular magnetization film such as Pt / Co or Pd / Co has a large perpendicular magnetic anisotropy and a high thermal stability. Large coercive force and easy squareness ratio 1.0 reasons such as that the value near to obtain, have been actively studied as a future high density recording medium (e.g., see Patent Documents 2 and 3).
[0005]
[Patent Document 1]
JP 2002-203306 A
[Patent Document 2]
JP 2002-025032 A
[Patent Document 3]
JP 2001-155329 A
[0006]
[Problems to be solved by the invention]
However, the level of medium noise reduction in such a conventional multi-layered perpendicular magnetic recording medium is still insufficient, and it is necessary to further improve the recording / reproducing characteristics by lowering the medium noise. .
The present invention has been made in view of the above problems, and an object of the present invention is to provide a perpendicular magnetic recording medium having a high recording density and excellent recording / reproducing characteristics, and a method for manufacturing the same, which can reduce medium noise. There is.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a perpendicular magnetic recording medium comprising a magnetic layer on a nonmagnetic substrate, wherein the magnetic layer is a first layer. The Co layer, which is the magnetic layer, and the Pt layer or Pd layer, which is the second magnetic layer, are alternately stacked, and is formed on at least one of the first magnetic layer and the second magnetic layer. Is characterized in that at least one element or oxide of Ru, Ta, Nb, Mo, Mn, Cr, Si, and Ni is added.
According to a second aspect of the present invention, in the perpendicular magnetic recording medium according to the first aspect, the addition amount is in a concentration range of 1 to 15 mol%.
According to a third aspect of the present invention, in the perpendicular magnetic recording medium according to the second aspect, the second magnetic layer is a Pt layer, and both the first and second magnetic layers contain Si oxide. The added amount of Si oxide in the Co layer as the first magnetic layer is 5 to 11 mol%, and the added amount of Si oxide in the Pt layer as the second magnetic layer is 1 to 8 mol%. It is characterized by that.
[0008]
The invention according to claim 4 is the perpendicular magnetic recording medium according to any one of claims 1 to 3, wherein each of the first magnetic layer and the second magnetic layer is 0.2 to 0.8 nm and It has a thickness of 0.05 to 1.2 nm.
According to a fifth aspect of the present invention, in the perpendicular magnetic recording medium according to any one of the first to fourth aspects, an underlayer is provided between the magnetic layer and the substrate, and the magnetic layer is directly above the underlayer. It is provided in.
The invention according to claim 6 is the perpendicular magnetic recording medium according to claim 5, wherein the underlayer is any one of a Pt film, a Pd film, a Ru film, or a Pt / Pd laminated film. .
The invention according to claim 7 is the perpendicular magnetic recording medium according to claim 5 or 6, wherein the thickness of the underlayer is 1 to 20 nm.
[0009]
According to an eighth aspect of the present invention, in the perpendicular magnetic recording medium according to any one of the fifth to seventh aspects, the orientation control layer for controlling the crystal orientation of the underlayer between the substrate and the underlayer. It is characterized by having.
The invention according to claim 9 is the perpendicular magnetic recording medium according to claim 8, wherein the orientation control layer is formed by laminating a first orientation control layer and a second orientation control layer, The composition of the second orientation control layer is set so that the underlayer is c-axis crystal oriented.
According to a tenth aspect of the present invention, in the perpendicular magnetic recording medium according to the ninth aspect, the first orientation control layer is a Ta layer, and the second orientation control layer is a NiFeCr layer, a NiFeNbB layer, or a NiFeSi layer. It is any one of these.
[0010]
The invention according to claim 11 is the perpendicular magnetic recording medium according to claim 9 or 10, wherein the first orientation control layer has a thickness of 1 to 10 nm, and the second orientation control layer has a thickness of 5 to 20 nm. It is characterized by being set in the range of.
A twelfth aspect of the present invention is the perpendicular magnetic recording medium according to any one of the ninth to eleventh aspects, wherein a soft magnetic backing layer is provided between the nonmagnetic substrate and the first orientation control layer. It is characterized by being.
The invention according to claim 13 is the perpendicular magnetic recording medium according to claim 12, wherein the backing layer has a CoZrNb or CoZrTa alloy composition and has a thickness of 50 to 400 nm.
The invention according to claim 14 is a method of manufacturing a perpendicular magnetic recording medium, wherein a Co layer as a first magnetic layer and a Pt layer or a Pd layer as a second magnetic layer are formed on a nonmagnetic substrate. A step of forming a magnetic layer by alternately laminating multiple layers, wherein the magnetic layer is formed by at least one element or oxide of Ru, Ta, Nb, Mo, Mn, Cr, Si, Ni Is performed by a sputtering method using a target to which is added in a concentration range of 1 to 15 mol%.
[0011]
According to a fifteenth aspect of the present invention, in the method for manufacturing a perpendicular magnetic recording medium according to the fourteenth aspect, the step of forming the magnetic layer comprises oxygen gas in a concentration range of 0.05 to 0.5% by mass flow ratio. The process is performed using the sputtering gas added in step (b).
According to a sixteenth aspect of the present invention, in the method for manufacturing a perpendicular magnetic recording medium according to the fourteenth or fifteenth aspect, prior to the formation of the magnetic layer, a Pt film, a Pd film, a Ru film, or a Pt / Pd is formed on the substrate. A step of sputter-depositing any underlayer of the laminated film is provided.
The invention according to claim 17 is the method of manufacturing a perpendicular magnetic recording medium according to claim 16, wherein the sputter film formation of the magnetic layer and the sputter film formation of the underlayer are performed by mixing Kr, Xe, Kr and Ar. One of the gases or a mixed gas of Xe and Ar is used as a sputtering gas.
[0012]
According to an eighteenth aspect of the present invention, in the method for manufacturing a perpendicular magnetic recording medium according to the sixteenth aspect, the surface of the underlayer is formed at a mass flow rate after the underlayer is formed and before the magnetic layer is formed. It is characterized by comprising a step of exposing the surface of the underlayer to oxygen by exposing it to Ar gas having a gas pressure of 0.1 to 10 Pa mixed with oxygen at a ratio of 1 to 10% for 1 to 20 seconds.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a conceptual diagram for explaining a basic configuration example of a perpendicular magnetic recording medium of the present invention. A backing layer 2 and an orientation control layer (3 and 4) are formed on a nonmagnetic substrate 1 such as Al or glass. ) And an underlayer 5 and a vertically oriented magnetic layer 6 are sequentially stacked, and a protective layer 7 is provided on the magnetic layer 6.
The basic feature of the perpendicular magnetic recording medium of the present invention is that the magnetic layer 6 is basically composed of a multilayer laminated film in which a Co layer and a Pt layer are laminated in multiple layers, and either or both of these Co layer and Pt layer are used. On the other hand, an oxide of an element such as Si is added, and the magnetic layer 6 having such a structure is formed on the underlayer 5 provided to reduce the magnetic interaction between the magnetic grains constituting the magnetic layer 6. This is the point that I tried to do. Here, the underlayer 5 is preferably composed of a Pt film, a Ru film, a Pd film, a Pt / Pd laminated film, or the like. Further, the composition of the oxide added to the magnetic layer 6 preferably satisfies the stoichiometric ratio. For example, when adding Si oxide, SiO 2 _x (0 <x ≦ 2), preferably SiO ₂ It is. The backing layer 2 and the orientation control layers (3 and 4) shown in FIG. 1 are layers that are preferably added between the underlayer 5 and the substrate 1 in order to improve the characteristics of the perpendicular magnetic recording medium. A perpendicular magnetic recording medium having no configuration of these layers may be used.
[0014]
More specifically, the underlayer 5 is made of a film such as Pt or Ru and has a thickness in the range of 1 to 20 nm, for example. If the magnetic layer 6 is formed after the surface of the underlayer 5 is subjected to oxygen adsorption treatment, the magnetic properties of the magnetic layer 6 can be further enhanced. That is, when oxygen is adsorbed on the surface of the underlayer 5, the magnetic interaction between the magnetic grains of the magnetic layer 6 formed on the underlayer 5 is suppressed, and the inclination of the magnetization curve near Hc becomes gentle. There is an advantage that recording and reproduction are facilitated.
The magnetic layer 6 is basically composed of a Co / Pt multilayer film, and is formed on both the Co layer, which is the first magnetic layer 6a, and the Pt layer, which is the second magnetic layer 6b, constituting the multilayer film. Si oxide (SiO _x ) To add Co-SiO ₂ / Pt-SiO ₂ A multilayer laminated film having a composition such as The Si oxide is preferably added in a concentration range of 1 to 15 mol%. For example, the Si oxide addition amount to the Co layer is 5 to 11 mol%, and the Si oxide addition amount to the Pt layer is 1 to 8 mol%. And
[0015]
In the above description, Si oxide is added to both the Co layer and the Pt layer. However, as already described, Si oxide may be added only to either the Co layer or the Pt layer. Good. Further, the magnetic layer 6 may be formed of a Co / Pt multilayer laminated film instead of a Co / Pt multilayer laminated film. In the case of a Co / Pd multilayer structure, Si oxide may be added to both the Co layer and the Pd layer, or Si oxide may be added only to either the Co layer or the Pd layer. . Further, instead of Si oxide (or together with Si oxide), at least one element or oxide of Ru, Ta, Nb, Mo, Mn, Cr, and Ni may be added.
In the perpendicular magnetic recording medium of the present invention, the provision of the underlayer 5 on which oxygen is adsorbed on the surface controls the inclination of the magnetization curve near the coercive force (Hc) of the magnetic layer 6 formed on the underlayer 5. The reason why the Co / Pt multilayer film is used for the magnetic layer 6 is that Hc is large and the squareness ratio is easily 1 as compared with a magnetic layer such as a Co—Cr alloy, and the interface magnetic anisotropy is utilized. This is because a large magnetocrystalline anisotropy can be obtained. The reason why the Si oxide is added to one or both of the Co layer and the Pt layer constituting the multilayer laminated film is to further improve the Hc of the medium and improve the recording / reproducing characteristics. That is, by adding Si oxide, nonmagnetic Si oxide is segregated between the magnetic grains constituting the Co layer and / or Pt layer, thereby miniaturizing and isolating individual magnetic grains. By doing so, Hc can be increased compared to a magnetic layer such as Co / Pt without addition of Si oxide, and high recording density can be achieved.
[0016]
The thickness of each layer constituting the magnetic layer 6 can be changed according to the target magnetic characteristics. For example, the Co layer has a thickness of 0.2 to 0.8 nm, and the Pt layer has a thickness of 0.05. The film thickness of the Co layer is preferably set in the range of 0.2 to 0.5 nm, and the film thickness of the Pt layer is preferably set in the range of 0.05 to 0.25 nm. The magnetic layer 6 is formed by sputtering using Ar, Kr, Xe, or a mixed gas thereof as a sputtering gas. As the sputtering gas, oxygen gas may be added in a mass flow ratio range of 0.05 to 0.5%.
The orientation control layers (3 and 4) are provided to increase the crystal orientation (c-axis orientation) of the underlayer 5, and preferably the Ta layer that is the first orientation control layer 3 and the second layer. It is configured as a two-layer structure in which a NiFeCr layer that is the orientation control layer 4 is laminated. The second orientation control layer may be a NiFeNbB layer or a NiFeSi layer. By increasing the c-axis orientation of the underlayer 5, the crystal orientation of the magnetic layer 6 provided on the underlayer 5 can be improved and the magnetic properties can be further enhanced. For example, when the Ta layer and the NiFeCr layer are configured as a two-layer structure, the thicknesses of the Ta layer and the NiFeCr layer are preferably 1 to 10 nm and 5 to 20 nm, respectively, and the composition of the NiFeCr layer is 50 for Ni. It is set appropriately so that the crystallinity and orientation of the Ru film as the underlayer 5 and the like are not lowered in a range of ˜70 at%, Fe of 10 to 20 at%, and Cr of 20 to 30 at%.
[0017]
The backing layer 2 is provided in order to increase the writing capability in the recording head, and is a soft magnetic film having a thickness of 50 to 400 nm, for example, and the composition thereof can be, for example, a composition of CoZrNb or CoZrTa.
Hereinafter, the present invention will be described in more detail with reference to examples.
(Example 1)
In this embodiment, the substrate 1 is a glass substrate, the backing layer 2 is a CoZrNb film, the underlayer 5 is a Pt film, the protective layer 7 is a carbon film, and the magnetic layer 6 is CoNi-SiO2. ₂ An example in which a Co layer that is the first magnetic layer 6a having the composition and a Pt layer 6b that is the second magnetic layer 6b having the Pt composition are stacked in layers will be described.
The manufacturing method of this perpendicular magnetic recording medium is as follows. The substrate 1 is a glass substrate having a thickness of 1 mm and a diameter of 3.5 inches. However, the diameter and thickness are not essential, and the substrate 1 may be an Al substrate on which Ni-P plating and an appropriate texture are formed.
[0018]
After the substrate 1 is sufficiently washed, a CoZrNb film is formed and the backing layer 2 is formed by a sputtering method. The sputter target used in this example has a composition of 87 at% Co-5 at% Zr-8 at% Nb. Ar gas was used as a sputtering gas, and an Ar gas pressure of about 1 Pa was formed to a thickness of about 200 nm at room temperature. The CoZrNb film has sufficient soft magnetic characteristics even in an amorphous state formed at room temperature.
A Pt underlayer 5 is formed by sputtering on the CoZrNb film continuously. The target used is pure Pt. The Kr gas has an Ar gas with a mass flow ratio of 4% and an O gas with a mass flow ratio of 0.2%. ₂ Sputtering was performed with a mixed gas mixed with a gas to form a film having a thickness of about 10 nm. The film forming temperature is room temperature and the gas pressure is about 5 Pa.
[0019]
Next, CoNi—SiO 2 is formed on the Pt underlayer 5. ₂ A magnetic layer 6 made of a / Pt multilayer laminated film is formed by sputtering. The target composition used was 95 mol% Co-5 at% Ni alloy for the Co layer and 10 mol% SiO. ₂ The Pt layer is pure Pt. By rotating these two targets simultaneously while discharging and sputtering, CoNi-SiO ₂ Layers and Pt layers are alternately stacked. Specifically, Kr or Xe gas is mixed with Ar gas with a mass flow ratio of 4% and O with a mass flow ratio of 0.2%. ₂ Sputtering is performed with a mixed gas mixed with gas, and the film thickness is CoNi-SiO ₂ The layer is 0.45 nm and the Pt layer is 0.4 nm. CoNi-SiO to be deposited ₂ The composition of the layer is 90 mol% (95 at% Co-5 at% Ni) -10 mol% SiO, reflecting the composition of the target used. ₂ It becomes. This film formation is performed at room temperature, and the gas pressure is 5 Pa.
[0020]
Finally, a carbon film is formed as a protective layer 7 on the outermost surface of the magnetic layer 6 by sputtering. The target was carbon, the sputtering gas was Ar gas, and the film was formed with a film thickness of about 7 nm. The film forming temperature is room temperature and the Ar gas pressure is about 1 Pa.
2 to 4 are diagrams for explaining the results of investigating the influence of sputtering gas on the characteristics of the magnetic layer 6 when the magnetic layer 6 is formed. FIG. 2 shows a pure Co layer (that is, Ni and SiO). ₂ Is a diagram showing the relationship between the Pt layer thickness and the coercive force of a film obtained by laminating a pure Pt layer with Ar, Kr, or Xe gas as a sputtering gas. The vertical axis represents the coercive force Hc, and the horizontal axis represents the Pt film thickness.
Sputter deposition using Ar gas shows a maximum coercivity of about 4000 Oe when the Pt film thickness is 0.2 nm, but when Kr gas is used, a maximum coercivity of about 4800 Oe is obtained at a Pt film thickness of 0.75 nm. Is used, a maximum coercive force of about 6000 Oe is obtained with a Pt film thickness of 1.0 nm. Thus, if the Pt film thickness that gives the maximum coercive force differs depending on the type of sputtering gas, and Kr or Xe is used as the sputtering gas, a perpendicular magnetic recording medium having a higher coercive force than when Ar gas is used. It can be seen that it can be produced.
[0021]
FIG. 3 shows an inclination (α) of a magnetization curve near Hc of a medium having a magnetic layer 6 in which a pure Co layer and a pure Pt layer are laminated in layers using Ar, Kr, or Xe gas as a sputtering gas. It is a figure for demonstrating Pt layer film thickness dependence, In this figure, the vertical axis | shaft is inclination (alpha) and a horizontal axis is Pt film thickness. The inclination α of the magnetization curve is an index indicating the magnitude of the magnetic interaction between the magnetic grains constituting the magnetic layer 6, and a smaller value is preferable.
The sputtered film formed with Ar gas has an α value of 3 or more, whereas when sputtered using Kr or Xe gas, the α value is approximately 1, reducing the magnetic interaction between the magnetic grains. I can see that That is, when the magnetic layer 6 is formed by sputtering using Kr or Xe gas, it is possible to suppress the magnetic interaction between the magnetic grains, and as a result, the medium noise is reduced.
[0022]
FIG. 4 is a diagram for explaining the dependency of the coercive force Hc on the sputtering gas pressure of a film in which a pure Co layer and a pure Pt layer are multilayered using Ar, Kr, or Xe gas as a sputtering gas. In this figure, the vertical axis represents the coercive force and the horizontal axis represents the gas pressure. The thicknesses of the Co layer and the Pt layer are set in the vicinity of the film thickness at which the maximum coercive force of each gas type can be obtained. In the case of Xe, the Co layer was 0.43 nm and the Pt layer was 0.87 nm. In the case of Kr, the Co layer was 0.44 nm and the Pt layer was 0.72 nm.
In the case of Ar gas, in the pressure range up to 10 Pa, the higher the gas pressure, the higher the Hc. On the other hand, in the case of Kr gas, the pressure indicating the maximum coercive force is 6.5 Pa, and in the case of Xe gas, the maximum coercive force is obtained at a gas pressure of 5 Pa. It can also be seen that the maximum coercive force itself is higher in the case of Kr gas and Xe gas than in the case of Ar gas.
[0023]
Table 1 summarizes the results of evaluating the magnetocrystalline anisotropy of a perpendicular magnetic recording medium having a magnetic layer 6 formed using Ar, Kr, and Xe sputtering gases. The larger the magnetocrystalline anisotropy constant (Ku), the higher the thermal stability and the better the medium.
[0024]
[Table 1]

[0025]
As shown in this table, it can be seen that a medium including the magnetic layer 6 formed by sputtering using Kr gas or Xe gas exhibits higher magnetocrystalline anisotropy than Ar gas.
Table 2 summarizes the magnetic cluster size of the magnetic layer 6 of each medium measured using a magnetic force microscope (MFM). The smaller the magnetic cluster size, the more advantageous the high recording density.
[0026]
[Table 2]

[0027]
As can be seen from this table, the magnetic cluster size can be reduced by using Kr gas or Xe gas as the sputtering gas compared to Ar gas, which is advantageous in improving the recording density. That is, when the magnetic layer 6 is formed, the magnetic characteristics of the perpendicular magnetic recording medium can be improved by using Kr gas or Xe gas as the sputtering gas.
Based on the results described above, Kr gas was selected as the sputtering gas, and various elements described above were added to the Co layer to improve the recording / reproducing characteristics.
FIG. 5 is a diagram for explaining the effect of adding oxygen gas to the sputtering gas at the time of forming the magnetic layer 6. Ni, Ta, Nb, Mo, Mn, Cr are added to the Co layer constituting the magnetic layer. , Si elements, and addition of oxygen gas having a mass flow ratio of 0 to 0.2% to Kr gas, which is a sputtering gas, and the amount of oxygen added to the coercive force of a perpendicular magnetic recording medium manufactured by sputtering In this figure, the vertical axis represents the coercive force and the horizontal axis represents the oxygen addition amount.
[0028]
Although the dependency of the coercive force on the amount of oxygen added varies depending on the type of additive element, it is confirmed that the coercive force is improved by the addition of oxygen. This is because the additive elements are oxidized by oxygen in the atmosphere to form oxides and precipitate between the Co particles, so that the magnetic interaction between the Co particles is reduced. This can also contribute to the improvement of recording / reproducing characteristics.
FIG. 6 shows a perpendicular magnetic recording medium (medium A) including a magnetic layer in which a layer obtained by adding 5 at% Ni to a Co layer (95 at% Co-5 at% Ni layer) and a Pt layer is laminated, and 95 at% Co -5at% Ni layer with SiO ₂ 10 mol% added layer (90 mol% (95 at% Co-5 at% Ni) -10 mol% SiO ₂ ) Is a diagram for explaining the recording / reproduction characteristics (SN characteristics) of a perpendicular magnetic recording medium (medium B) having a magnetic layer in which a Pt layer and a multi-layer are laminated. Is the linear recording density. For comparison, the recording / reproducing characteristics (SN characteristics) of a perpendicular magnetic recording medium (medium C) including a magnetic layer in which a pure Co layer and a Pt layer are laminated are also shown. The magnetic layers of these media were all formed by sputtering with oxygen gas having a mass flow ratio of 0.2% added to Kr gas, and evaluation of recording / reproduction characteristics was performed using a ring head for in-plane media. Executed.
[0029]
In medium C, recording / reproduction can only be performed up to a recording density of about 400 kFCI, but in medium A, the SNR is remarkably improved in the region of 200 kFCI or higher compared to medium C, and it is confirmed that sufficient recording / reproduction can be performed up to 550 kFCI. It was. In addition, the SNR is further improved in the medium B than in the medium A. Thus, Ni or SiO is formed on the Co layer. ₂ It has been confirmed that the recording / reproducing characteristics are improved by adding a metal or an oxide such as the above, which is effective in improving the recording density.
(Example 2)
In this example, a perpendicular magnetic recording medium in which the magnetic layer 6 has a CoRu / Pt multilayer structure and a CoZrNb film as the backing layer 2 was produced.
The manufacturing method of this perpendicular magnetic recording medium is as follows. The substrate 1 is a glass substrate having a thickness of 1 mm and a diameter of 3.5 inches. However, the diameter and thickness are not essential, and the substrate 1 may be an Al substrate having an appropriate texture formed by Ni-P plating.
[0030]
After the substrate 1 is sufficiently washed, a CoZrNb film is formed and the backing layer 2 is formed by a sputtering method. The sputter target used in this example has a composition of 87 at% Co-5 at% Zr-8 at% Nb. Ar gas was used as a sputtering gas, and an Ar gas pressure of about 1 Pa was formed to a thickness of about 200 nm at room temperature. The CoZrNb film has sufficient soft magnetic characteristics even in an amorphous state formed at room temperature.
A Pt underlayer 5 is formed by sputtering on the CoZrNb film continuously. The target used is pure Pt. A Kr gas with Ar gas having a mass flow ratio of 4% and O with a mass flow ratio of 0.2% ₂ Sputtering was performed with a mixed gas mixed with a gas to form a film having a thickness of about 10 nm. The film forming temperature is room temperature and the gas pressure is about 5 Pa.
[0031]
Next, a magnetic layer 6 made of a CoRu / Pt multilayer film is formed on the Pt underlayer 5 by sputtering. The target composition used was 95 at% Co-5 at% Ru for the Co layer and pure Pt for the Pt layer, and the CoRu layers and the Pt layers were alternately stacked by rotating these targets while simultaneously discharging and sputtering them. Let The Kr gas has an Ar gas with a mass flow ratio of 4% and an O gas with a mass flow ratio of 0.2%. ₂ Sputtering is performed with a mixed gas in which a gas is mixed, and the film thickness is 0.45 nm for the CoRu layer and 0.8 nm for the Pt layer. This film formation is performed at room temperature, and the gas pressure is 5 Pa.
Finally, a carbon film is formed as a protective layer 7 on the outermost surface of the magnetic layer 6 by sputtering. The target was carbon, the sputtering gas was Ar gas, and the film was formed with a film thickness of about 7 nm. The film forming temperature is room temperature and the Ar gas pressure is about 1 Pa.
[0032]
FIG. 7 shows a perpendicular magnetic recording medium (medium D) including a magnetic layer in which a Co layer is added with 5 at% Ru (95 at% Co-5 at% Ru layer) and a Pt layer, and 95 at% O in Co-5at% Ru layer ₂ 0.2 mol% added layer (99.8 mol% (95 at% Co-5 at% Ru) -0.2 mol% O ₂ ) Is a diagram for explaining the recording / reproducing characteristics (SN characteristics) of a perpendicular magnetic recording medium (medium E) having a magnetic layer in which a layer is laminated with a Pt layer. Linear recording density. For comparison, the recording / reproduction characteristics (SN characteristics) of a perpendicular magnetic recording medium (medium F) including a magnetic layer in which a pure Co layer and a Pt layer are laminated are also shown. The magnetic layers of these media are all formed by sputtering with Kr gas added with oxygen gas having a mass flow rate ratio of 0 to 0.2%. Run with the head.
[0033]
The medium F was able to record / reproduce only up to a recording density of about 500 kFCI, but the medium D had an improved SNR compared to the medium F, and it was confirmed that sufficient recording / reproduction was possible up to 500 kFCI. Further, the SNR is further improved in the medium E than in the medium D.
Thus, Ru is added to the Co layer, or at the same time O ₂ It was confirmed that the recording / reproduction characteristics were improved by adding, which was effective in improving the recording density.
(Example 3)
As shown in FIG. 1, the perpendicular magnetic recording medium of this example has a soft magnetic backing layer 2, a first orientation control layer 3, and a second orientation control on a nonmagnetic substrate 1 such as Al. The layer 4, the underlayer 5, the magnetic layer 6 having a multilayered laminated structure, and the carbon protective layer 7 are sequentially laminated.
[0034]
Co—SiO which is the first magnetic layer 6a as the magnetic layer 6 ₂ Co-SiO in which multiple layers and Pt layers as second magnetic layers 6b are alternately stacked ₂ / Pt and Co to SiO ₂ Nonmagnetic SiO between Co particles by adding ₂ The Co particles are segregated to refine and isolate the Co particles. This Co-SiO ₂ SiO in the layer ₂ The addition amount is preferably set to 2 to 15 mol%, more preferably 5 to 11 mol%.
Further, by using a Ru underlayer having oxygen adsorbed on the surface as the underlayer 5, the gradient of the magnetization curve in the vicinity of Hc is moderated to reduce the magnetic interaction between the grains of the perpendicular magnetic layer, and recording / reproduction is performed. Has been made easier.
Further, for the purpose of improving the coercive force by orienting the crystals of the Ru underlayer 5 with c-axis, the Ta layer is used as the first orientation control layer 3 and the NiFeCr as the second orientation control layer 4 for controlling the crystal orientation. Use layers. The composition of the NiFeCr layer in this case is appropriately selected within a range that does not deteriorate the crystallinity improvement and crystal orientation controllability of the Ru underlayer 5 provided on the NiFeCr layer. For example, 50 to 70 at% Ni-10 to 20 at% It is set in the range of Fe-20 to 30 at% Cr.
[0035]
The thickness of each layer is preferably 1 to 10 nm for the first orientation control layer 3, 5 to 15 nm for the second orientation control layer 4, and 10 to 20 nm for the underlayer 5. Co-SiO ₂ The thickness of the layer is set in the range of 0.2 to 0.8 nm, and the thickness of the Pt layer is set in the range of 0.1 to 1 nm.
In addition to these layers, a soft magnetic CoZrTa backing layer 2 having a film thickness in the range of 50 to 400 nm is provided between the nonmagnetic substrate 1 and the first orientation control layer 3, so that the writing capability of the recording head is achieved. Can be increased.
A method for manufacturing the perpendicular magnetic recording medium having the above configuration will be described below. The nonmagnetic substrate to be used is an Al substrate having a diameter of 3.5 mm and a thickness of 1 mm. However, the diameter and thickness are not essential, and a glass substrate may be used as the substrate.
[0036]
After thoroughly cleaning the substrate, a soft magnetic CoZrTa is formed by sputtering to form a backing layer. The target used here has a composition of 92 at% Co-5 at% Zr-3 at% Ta. Ar gas was used as the sputtering gas, and the film was formed to a thickness of about 200 nm at room temperature under a gas pressure of about 1 Pa. CoZrTa has sufficient soft magnetic properties even in an amorphous state formed at room temperature.
On the CoZrTa film, the first orientation control layer 3 of Ta is continuously formed by sputtering. The target used is pure Ta. Sputtering was performed with Ar gas to form a film having a thickness of about 5 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa.
On the Ta film, the second orientation control layer 4 of NiFeCr is continuously formed by sputtering. The composition of the target used is 60 at% Ni-15 at% Fe-25 at% Cr. Sputtering was performed with Ar gas to form a film having a thickness of about 10 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa.
[0037]
On this NiFeCr film, a Ru film as the underlayer 5 is formed by sputtering. The target used is pure Ru. Sputtering was performed with Ar gas to form a film with a thickness of about 20 nm. The film forming temperature is room temperature and the gas pressure is about 4 Pa. The surface of the Ru underlayer formed in this way is changed to an Ar gas under a pressure of 0.1 to 10 Pa and an O gas having a mass flow rate ratio of 1 to 10%. ₂ An appropriate amount of oxygen was adsorbed on the Ru surface by exposure to an atmosphere in which gas was mixed for about 1 to 20 seconds.
Next, Co—SiO 2 is formed on the Ru underlayer 5. ₂ A vertically oriented magnetic layer 6 made of a / Pt multilayer film is formed by sputtering. The target used was 9 mol% SiO in Co. ₂ (91 mol% Co-9 mol% SiO ₂ ) Target and pure Pt. By rotating these two targets simultaneously while discharging and sputtering, Co-SiO ₂ Layers and Pt layers are alternately stacked. In addition, the formed Co-SiO ₂ The composition of the layer reflects 91 mol% Co-9 mol% SiO reflecting the composition of the target used. ₂ It is. Sputtering with Ar gas, film thickness is Co-SiO ₂ The layer is 0.3 nm and the Pt layer is 0.1 nm. This film formation is performed at room temperature, and the gas pressure is 5 Pa.
[0038]
Finally, a nitrogen-doped carbon (C: N) film was formed as a protective layer 7 on the outermost surface of the magnetic layer 6 with a film thickness of about 7 nm by a sputtering method. The film forming temperature is room temperature and the Ar gas pressure is about 1 Pa.
FIG. 8 is a diagram for explaining the effect of the crystal orientation control layer provided in the perpendicular magnetic recording medium of the present invention, in which a Ta layer and a NiFeCr layer which are first and second orientation control layers are sequentially formed. Ru base layer 5 is formed, and further Co-SiO ₂ This is an X-ray diffraction pattern obtained from a sample in which a magnetic layer 6 having a / Pt multilayer structure is formed. From this figure, diffraction is observed only from the (002) plane from the Ru underlayer 5, and the orientation control layers (3 and 4) effectively act to c-orient the Ru underlayer 5. I understand that.
[0039]
FIG. 9 is a diagram for explaining the effect of adsorbing oxygen on the surface of the underlayer 5 of Ru, and is a magnetization curve obtained from the perpendicular magnetic recording medium BR> of the present invention produced by the method described above. . The unit of the horizontal axis is Oe, and the unit of the vertical axis is emu. In this figure, the inclination of the magnetization curve near the coercive force Hc is small, indicating that the magnetic interaction between the magnetic grains constituting the magnetic layer is small. That is, by adsorbing oxygen to the surface of the Ru underlayer 5, there is an effect that recording / reproduction is facilitated.
Table 3 shows the Co-SiO of this example. ₂ The coercive force (Hc), squareness ratio (S), saturation magnetization (Ms), reverse domain nucleation magnetic field (Hn), and slope of the magnetization curve (α) of the medium including the / Pt magnetic layer, and boron (B) in Co The results of comparison with the coercive force of a medium including a Co—B / Pt magnetic layer (conventional product) in which a Co—B layer to which Pt is added and a Pt layer are laminated are summarized. Note that a Pt layer was used as a base layer of the Co—B / Pt magnetic layer.
[0040]
[Table 3]

[0041]
Co-SiO ₂ The coercive force of the / Pt magnetic layer is 1000 Oe or more higher than that of the Co—B / Pt magnetic layer, and the slope (α) of the magnetization curve is greatly reduced from 8.5 to 1.8. Yes. That is, Co—SiO 2 is formed on the Ru underlayer 5. ₂ By perpendicularly laminating layers and Pt layers, it is possible to obtain a perpendicular magnetic recording medium that can simultaneously achieve a high coercive force and a gentle inclination of the magnetization curve.
Table 4 summarizes the results of evaluation of the magnetocrystalline anisotropy of these two perpendicular magnetic recording media. The larger the magnetocrystalline anisotropy constant (Ku), the higher the thermal stability of the media. To do.
[0042]
[Table 4]

[0043]
As can be seen from this table, Co-SiO ₂ The Ku of the / Pt magnetic layer is slightly higher than the Ku of the Co—B / Pt magnetic layer, indicating that the thermal stability is improved. Thus, it can be understood that the perpendicular magnetic recording medium of the present invention exhibits excellent magnetic characteristics as compared with the conventional perpendicular magnetic recording medium.
FIG. 10 is a diagram for explaining the reproduction output as the recording / reproduction characteristics of the conventional product and the product of the present invention. The horizontal axis of this graph is the linear recording density, and the vertical axis is the TAA (Track Average Amplitude). It is. For this evaluation, a ring head for an in-plane medium is used. The conventional product in which the Co—B layer and the Pt layer are stacked on the Pt underlayer can reproduce only the recording density of about 400 kFCI, whereas the Co—SiO layer is formed on the Ru underlayer. ₂ In a medium having a magnetic layer in which a layer and a Pt layer are laminated, a reproduction signal is detected even at 540 kFCI or more, and it can be seen that reproduction is possible up to a high linear recording density.
[0044]
FIG. 11 is a diagram for explaining medium noise which is a recording / reproducing characteristic of the conventional product and the product of the present invention. The horizontal axis of this graph is the linear recording density, and the vertical axis is the noise. A ring head for in-plane media is also used for this evaluation. In the conventional product in which the Co—B layer and the Pt layer are laminated on the Pt underlayer, the noise output is reduced at 200 kFCI or more, indicating that the recording / reproduction is not sufficiently performed, and the noise itself. Is also big. On the other hand, Co—SiO 2 is formed on the Ru underlayer. ₂ In the product of the present invention in which the layer and the Pt layer are laminated, noise increase is confirmed up to 540 kFCI in addition to lower noise than the conventional product at all linear recording densities, and sufficient recording / reproduction characteristics are obtained. Yes.
FIG. 12 is a diagram for explaining the SNR, which is the recording / reproducing characteristic of the conventional product and the product of the present invention. The horizontal axis of this graph is the linear recording density, and the vertical axis is the SNR. A ring head for in-plane media is also used for this evaluation. Compared to the conventional product in which a Co-B layer and a Pt layer are laminated, Co-SiO ₂ In the product of the present invention in which the layer and the Pt layer are laminated, the recording / reproduction is sufficiently performed up to 540 kFCI with an overwhelmingly high SNR at all linear recording densities.
[0045]
Thus, it can be seen that the configuration of the perpendicular magnetic recording medium of the present invention is effective in improving the recording / reproducing characteristics and contributes to the improvement of the recording density.
(Example 4)
The perpendicular magnetic recording medium of this example uses an Al substrate as the substrate 1, and a CoZrNb soft magnetic backing layer 2, a two-layer orientation control layer (3 and 4), and a Ru underlayer 5 are sequentially laminated thereon. In addition, Co-SiO ₂ A magnetic layer 6 in which a large number of layers and Pt layers are stacked is provided. In the alignment control layer of this example, the Ta layer 3 is used as the first layer, and the NiFeNbB layer 4 is used as the second layer. The Al substrate used here has a diameter of 3.5 inches and a thickness of 1 mm. However, the diameter and thickness are not essential, and a glass substrate may be used instead of the Al substrate.
[0046]
The manufacturing process of this perpendicular magnetic recording medium will be described below.
After thoroughly cleaning the substrate, soft magnetic CoZrNb is formed by sputtering to form the backing layer 2. The target used here has a composition of 87 at% Co-5 at% Zr-8 at% Nb. Ar gas was used as the sputtering gas, and the film was formed to a thickness of about 200 nm at room temperature under a gas pressure of about 1 Pa. CoZrNb has sufficient soft magnetic properties even in an amorphous state formed at room temperature.
On the CoZrNb soft magnetic film, a Ta layer which is the first orientation control layer 3 is continuously formed by sputtering. The target used is pure Ta. Sputtering was performed with Ar gas to form a film having a thickness of about 5 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa.
[0047]
A NiFeNbB layer that is the second orientation control layer 4 is formed by sputtering on the Ta film continuously. The target used has a composition of 79 at% Ni-12 at% Fe-3 at% Nb-6 at% B. Sputtering was performed with Ar gas to form a film with a thickness of about 30 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa.
On this NiFeNbB layer, a Ru film as the underlayer 5 is formed by sputtering. The target used is pure Ru. Sputtering was performed with Ar gas to form a film with a thickness of about 20 nm. The film forming temperature is room temperature and the gas pressure is about 4 Pa. The surface of the Ru underlayer 5 thus formed is coated with Ar gas at a pressure of 1 Pa and a mass flow ratio of 2%. ₂ An appropriate amount of oxygen is adsorbed on the surface of Ru by exposing it to an atmosphere mixed with gas for about 10 seconds.
[0048]
Next, Co—SiO 2 is formed on the Ru underlayer 5. ₂ A vertically oriented magnetic layer 6 made of a / Pt multilayer film is formed by sputtering. The target used was Co-SiO ₂ 91 mol% Co-9 mol% SiO for layer deposition ₂ Or 94 mol% Co-6 mol% SiO ₂ This is a pure Pt target for forming a Pt layer. By rotating these two targets simultaneously while discharging and sputtering, Co-SiO ₂ Layers and Pt layers are alternately stacked. Sputtering with Ar gas, film thickness is Co-SiO ₂ The layer is 0.3 nm and the Pt layer is 0.1 nm. This film formation is performed at room temperature, and the gas pressure is 5 Pa. Co-SiO obtained in this way ₂ The composition of the layer reflects the composition of the target, 91 mol% Co-9 mol% SiO ₂ Or 94 mol% Co-6 mol% SiO ₂ It is.
[0049]
Finally, a nitrogen-doped carbon (C: N) film is formed as a protective layer 7 on the outermost surface of the magnetic layer 6 by a sputtering method. The target is carbon, the sputtering gas is Ar gas, and the mass flow ratio is 4%. ₂ A gas mixture was used to form a mixed gas having a film thickness of about 7 nm. The film forming temperature is room temperature and the Ar gas pressure is about 1 Pa.
FIG. 13 shows the Co—SiO constituting the magnetic layer 6. ₂ FIG. 13A is a planar TEM image for explaining the state of the magnetic particle diameter and the nonmagnetic grain boundary width in the layer. FIG. ₂ A sample with an addition amount of 6 mol%, FIG. ₂ A sample with an addition amount of 9 mol%. When this TEM image is analyzed, SiO ₂ The sample with an addition amount of 6 mol% (FIG. 13A) has an average magnetic particle diameter of 7.1 nm and an average grain boundary width of 1.5 nm, whereas SiO 2 ₂ It can be seen that the sample with an addition amount of 9 mol% (FIG. 13B) has an average magnetic particle diameter of 5.6 nm and an average grain boundary width of 1.6 nm. That is, added SiO ₂ It can be seen that the larger the amount, the smaller the average particle size of the magnetic particles and the larger the average grain boundary width. In general, when the magnetic crystal grain size is reduced, the magnetic interaction between the particles is weakened, and the degree of isolation of the individual magnetic grains is increased, which is suitable for achieving a high recording density.
[0050]
FIG. 14 is a diagram for explaining the change in magnetic characteristics when the thickness of the Pt layer, which is the second magnetic layer 6b, is changed. FIG. 14 (a) shows the coercive force Hc, and FIG. 14 (b). Is the Pt film thickness dependence of the slope α of the magnetization curve. When the Pt film thickness is zero (when no Pt film is provided), the Hc value is zero, whereas the Hc value is about 6000 Oe at a film thickness of 0.12 nm. The Hc value decreases to about 1200 Oe at a Pt film thickness of 0.25 nm, and the Hc value gradually decreases as the film thickness increases. On the other hand, the α value shows α = 1.5 at a Pt film thickness of 0.12 nm, and shows a tendency to increase as the Pt film thickness increases. Thus, it is desirable that the thickness of the Pt layer is small. In this embodiment, 0.12 nm is optimal.
FIG. 15 is a diagram for explaining a change in magnetic characteristics when the film thickness of the NiFeNbB layer 4 is changed. FIG. 15A shows noise at a recording / reproducing characteristic of 400 kFCI, and FIG. Is the SNR at 400 kFCI. For comparison, the magnetic characteristics when a NiFeCr layer having a thickness of 10 nm is provided instead of the NiFeNbB layer are also shown.
[0051]
As shown in FIG. 15 (a), the noise tends to decrease as the NiFeNbB film thickness is increased from 10 nm to 30 nm. When the NiFeNbB film thickness is 30 nm, the noise is higher than when a 10 nm thick NiFeCr layer is provided. The level is lowered. Further, as shown in FIG. 15B, the SNR value when the NiFeNbB film is provided is higher than that when the NiFeCr film having a thickness of 10 nm is used regardless of the film thickness.
Thus, SiO into the Co layer ₂ By controlling the addition amount, the magnetic grain size and the width of the non-magnetic grain boundary layer can be controlled, and by optimizing the film thickness of the Pt layer, high Hc can be obtained, and further provided immediately below the Ru layer. The layer and the NiFeCr layer of Example 3 are changed to a NiFeNbB layer of 10 to 30 nm to improve noise and SNR. In this way, a perpendicular magnetic recording medium capable of achieving a higher recording density can be produced.
(Example 5)
The perpendicular magnetic recording medium of this example is a medium having substantially the same configuration as that described in Example 4, but the magnetic layer 6 provided on the Ru underlayer 5 is made of Co—SiO 2. ₂ / Pd multilayer structure is different. The target composition used to form the magnetic layer 6 was 91 mol% Co-9 mol% SiO. ₂ The composition and pure Pd, and these targets are simultaneously discharged and rotated while being sputtered, so that Co-SiO ₂ Layers and Pd layers are alternately stacked. Sputtering with Ar gas, film thickness is Co-SiO ₂ The layer is 0.3 nm and the Pd layer is 0.72 nm. This film formation is performed at room temperature, and the gas pressure is 5 Pa.
[0052]
FIG. 16 is a diagram for explaining changes in magnetic characteristics when the thickness of the Pd layer, which is the second magnetic layer 6b, is changed. FIG. 16A shows the coercive force Hc, and FIG. Is the Pd film thickness dependence of the slope α of the magnetization curve. As the Pd film becomes thicker, the Hc value becomes higher and settles to a substantially constant value (about 5500 Oe) at a Pd film thickness of 0.72 nm. On the other hand, the α value hardly depends on the Pd film thickness, and shows a value of around 2, indicating that the magnetic interaction between the magnetic particles is sufficiently small.
FIG. 17 shows Co-SiO ₂ FIG. 17A is noise for recording / reproduction characteristics, and FIG. 17B is SNR for explaining the effect of the Ru underlayer 5 on the magnetic characteristics of the magnetic layer 6 having a / Pd multilayer structure. is there. For comparison, the case where a Pt film and a Pd film are used as the underlayer is also shown. As shown in FIG. 17A, when a Pt film or a Pd film is used as the underlayer, noise is large and sufficient recording / reproduction cannot be performed at a high linear recording density. It can be seen that noise is small and sufficient recording / reproduction is performed up to a high linear recording density. In addition, the SNR value shown in FIG. 17 (b) is much better when the Ru film is used.
[0053]
FIG. 18 shows the Co—SiO of the present invention described in Example 4. ₂ / Pt multilayer magnetic structure perpendicular magnetic recording medium comprising a magnetic layer, and Co-SiO2 of Example 5 ₂ FIG. 18A is a diagram for explaining recording / reproduction characteristics with a perpendicular magnetic recording medium having a magnetic layer having a / Pd multi-layer structure, FIG. 18A is a reproduction output (TAA) characteristic, FIG. 18B is a noise characteristic, and FIG. 18 (c) is the SNR characteristic. Co-SiO for both reproduction output and noise ₂ The perpendicular magnetic recording medium having a magnetic layer of / Pd multilayer structure is smaller, but the SNR is CoSiO ₂ / Pt is almost equivalent to a perpendicular magnetic recording medium having a magnetic layer having a multilayer structure. Thus, as the magnetic layer, CoSiO ₂ Even if the / Pd multilayer structure is adopted, an excellent perpendicular magnetic recording medium can be manufactured by providing the Ru film as the underlayer.
(Example 6)
In this example, the substrate 1 is an Al substrate, the backing layer 2 is a CoZrNb film, the orientation control layer has a two-layer structure of a Ta layer 3 and a NiFeCr layer 4, the underlayer 5 is a Ru film, and the magnetic layer 6 is a Co-SiO2 layer. ₂ Co layer of composition and Pt-SiO ₂ An example in which a Pt layer having a composition is laminated in multiple layers will be described. The protective layer 7 is a carbon film.
[0054]
The manufacturing method of this perpendicular magnetic recording medium is as follows. The substrate 1 is an Al substrate having a thickness of 1 mm and a diameter of 3.5 inches, but its diameter and thickness are not essential and may be a glass substrate.
After the substrate 1 is sufficiently washed, a CoZrNb film is formed and the backing layer 2 is formed by a sputtering method. The sputter target used in this example has a composition of 87 at% Co-5 at% Zr-8 at% Nb. An Ar gas was used as a sputtering gas, and an Ar gas pressure of about 1 Pa was formed at a room temperature to a thickness of about 200 nm. The CoZrNb film has sufficient soft magnetic characteristics even in an amorphous state formed at room temperature.
On the CoZrNb film, a Ta layer as the first orientation control layer 3 is continuously formed by sputtering. The target used is pure Ta. Sputtering was performed with Ar gas to form a film with a thickness of about 3 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa. A NiFeCr layer as the second orientation control layer 4 is formed by sputtering on the Ta layer continuously. The target used has a composition of 60 at% Ni-15 at% Fe-25 at% Cr. Sputtering was performed with Ar gas to form a film having a thickness of about 10 nm. The film forming temperature is room temperature and the gas pressure is about 1 Pa. These Ta layer and NiFeCr layer constitute an orientation control layer, and the Ru film as the underlayer 5 formed thereon is c-axis oriented.
[0055]
A Ru film is formed by sputtering on the NiFeCr layer to form the underlayer 5. The target used is pure Ru. Sputtering was performed with Ar gas to form a film with a thickness of about 20 nm. The film forming temperature is room temperature and the gas pressure is about 4 Pa. The surface of the base layer 5 formed in this way is O gas having a mass flow rate ratio of 2% to Ar gas under a pressure of 1 Pa. ₂ An appropriate amount of oxygen is adsorbed on the surface of the Ru film by exposure to a mixed gas atmosphere mixed with gas for about 10 seconds. By adsorbing oxygen to the surface of the underlayer 5, the gradient of the magnetization curve in the vicinity of Hc of the magnetic layer 6 is moderated to reduce the magnetic interaction between the magnetic grains constituting the magnetic layer.
Next, Co—SiO 2 is formed on the base layer 5 of the Ru film. ₂ / Pt-SiO ₂ A vertically oriented magnetic layer composed of a multilayer film is formed by sputtering. The targets used for film formation were 91 to 94 mol% Co-6 to 9 mol% SiO, respectively. ₂ And 95 mol% Pt-5 mol% SiO ₂ By rotating these targets while simultaneously discharging and sputtering these targets, Co—SiO 2 is obtained. ₂ Layer and Pt-SiO ₂ Layers are stacked alternately. Sputtering with Ar gas, film thickness is Co-SiO ₂ Layer 0.3nm, Pt-SiO ₂ The layer is 0.07 to 0.25 nm. This film formation is performed at room temperature, and the gas pressure is 5 Pa.
[0056]
Finally, a nitrogen-doped carbon (C: N) film is formed as a protective layer 7 on the outermost surface of the magnetic layer 6 by a sputtering method. The target is carbon, the sputtering gas is Ar gas, and the mass flow ratio is 4%. ₂ A gas mixture was used to form a mixed gas having a film thickness of about 7 nm. The film forming temperature is room temperature and the Ar gas pressure is about 1 Pa.
FIG. 19 shows 91 mol% Co-9 mol% SiO. ₂ / 95 mol% Pt-5 mol% SiO ₂ Magnetic layer composed of multilayer laminated film, and 94 mol% Co-6 mol% SiO ₂ / 95 mol% Pt-5 mol% SiO ₂ Magnetic layer composed of multilayer laminated film, and 91 mol% Co-9 mol% SiO ₂ FIG. 6 is a diagram for explaining the dependency of each Hc of a perpendicular magnetic recording medium including a magnetic layer formed of a / Pt multilayer film on the film thickness of a second magnetic layer 6b. SiO to the Co layer which is the first magnetic layer ₂ When the addition amount of 9 mol%, SiO is added to the Pt layer. ₂ Hc of the medium with 5 mol% added is SiO ₂ The value is about 300 to 500 Oe lower than that of the additive-free medium, but the SiO layer to the Co layer ₂ It can be seen that the medium with an addition amount of 6 mol% shows extremely high Hc.
[0057]
FIG. 20 is a diagram for explaining the dependence of the inclination α around the Hc of each of the three types of perpendicular magnetic recording media on the film thickness of the second magnetic layer 6b. It can be seen that there is an optimum film thickness of the second magnetic layer that minimizes the α value in any medium. Further, 91 mol% Co-9 mol% SiO ₂ / 95 mol% Pt-5 mol% SiO ₂ A medium having a magnetic layer composed of a multilayer film, and 91 mol% Co-9 mol% SiO ₂ As compared with a medium having a magnetic layer composed of a / Pt multilayer laminated film, the Pt layer has SiO 2 ₂ In the medium to which is added, the α value is as low as about 0.15 to 0.4 in any thickness of the second magnetic layer. Considering that α is a measure of the magnitude of the magnetic interaction between the magnetic grains, SiO is added to the Pt layer. ₂ This means that the degree of magnetic interaction between the magnetic grains is reduced and noise is reduced.
[0058]
FIG. 21 shows 91 mol% Co-9 mol% SiO. ₂ / 95 mol% Pt-5 mol% SiO ₂ A medium having a magnetic layer composed of a multilayer film, and 91 mol% Co-9 mol% SiO ₂ FIG. 6 is a diagram for explaining the dependence of each magnetic anisotropy constant Ku on the thickness of a second magnetic layer 6b of a perpendicular magnetic recording medium including a magnetic layer formed of a / Pt multilayer laminated film. Both media show substantially the same Ku value, and SiO into the Pt layer ₂ This means that there is no decrease in Ku due to the addition of.
FIG. 22 shows SiO in the Hc Co layer. ₂ In order to examine the dependency on the amount of addition, 18 to 38% by volume of SiO is added to the Co layer. ₂ Co-SiO added with ₂ This is a summary of the results of measuring the Hc of each medium produced by preparing a medium having a magnetic layer comprising a / Pt multilayer laminated film. Hereinafter, conversion of mol% and volume% is performed by the following formula.
[0059]
SiO in Co ₂ The volume% of [(SiO ₂ Mol% / 100) * SiO ₂ Volume at 1 mole * 100] / [(SiO ₂ Mol% / 100) * SiO ₂ Volume at 1 mole + {1- (SiO ₂ Mol% / 100)} * volume in mol of Co]. SiO in Pt ₂ The volume% of [(SiO ₂ Mol% / 100) * SiO ₂ Volume at 1 mole * 100] / [(SiO ₂ Mol% / 100) * SiO ₂ Volume at 1 mole + {1- (SiO ₂ Mol% / 100)} * volume in mol of Pt]. Where SiO ₂ , Co, Pt volume in 1 mole (cm ³ ) Were 23.11, 6.58, and 9.09, respectively.
As shown in FIG. 22, the Hc of the medium is SiO to the Co layer. ₂ It decreases rapidly as the amount added increases. This is because SiO is present at the grain boundary between magnetic grains. ₂ This means that if H is segregated to increase the isolation of individual magnetic grains to reduce noise, high Hc cannot be obtained.
[0060]
FIG. 23 shows SiO into the Pt layer of Hc. ₂ It is a figure for demonstrating the addition effect, and is 18-38 volume% SiO in Co layer. ₂ In addition to SiO in the Pt layer ₂ To add Co-SiO ₂ / Pt-SiO ₂ Media having multilayer laminated magnetic layers were prepared, and Hc of these media was changed to SiO in the Pt layer. ₂ Co-SiO without the addition of ₂ FIG. 4 summarizes the results of comparison with Hc of a medium including a / Pt multilayer laminated film magnetic layer.
As already explained with reference to FIG. 22, the Pt layer is made of SiO. ₂ SiO is added only to the Co layer. ₂ In the case of a medium to which is added, SiO into the Co layer ₂ When the amount of addition increases, Hc decreases rapidly, but SiO to the Co layer increases. ₂ In addition to the addition, the Pt layer also has SiO ₂ It can be seen that when H is added, the decreasing tendency of Hc is alleviated. That is, not only the Co layer but also the Pt layer is made of SiO. ₂ If added, more SiO in the medium giving the same Hc ₂ Addition becomes possible. As a result, at the grain boundary between magnetic grains, SiO ₂ It is easy to reduce noise by increasing the segregation of individual magnetic grains and increasing the isolation of individual magnetic grains.
[0061]
【The invention's effect】
As described above, the perpendicular magnetic recording medium of the present invention is basically composed of a multilayer film in which the magnetic layer is formed by laminating a Co layer and a Pt layer (or Pd layer), and the Co layer In order to reduce the magnetic interaction between the magnetic grains constituting the magnetic layer by adding an oxide of an element such as Si to both or either of the Pt layers (or Pd layers). It was formed on a base layer such as a Ru film provided on the substrate. Prior to the formation of the magnetic layer, the surface of the underlayer was subjected to an oxygen adsorption treatment to suppress the magnetic interaction between the magnetic grains of the magnetic layer. This makes it possible to provide a perpendicular magnetic recording medium having a high recording density and excellent recording / reproducing characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration example of a perpendicular magnetic recording medium of the present invention.
FIG. 2 is a diagram showing the relationship between the Pt layer thickness and the coercive force of a film in which a pure Co layer and a pure Pt layer are multilayered using Ar, Kr, or Xe gas as a sputtering gas.
FIG. 3 explains the dependency of the slope of the magnetization curve near Hc on the Pt layer thickness of a film in which a pure Co layer and a pure Pt layer are multilayered using Ar, Kr, or Xe gas as a sputtering gas. FIG.
FIG. 4 is a diagram for explaining the dependency of the coercive force Hc on the sputtering gas pressure of a film in which a pure Co layer and a pure Pt layer are multilayered using Ar, Kr, or Xe gas as a sputtering gas. .
FIG. 5 is a diagram for explaining the effect of adding an oxygen gas to a sputtering gas when forming a magnetic layer.
FIG. 6 shows a perpendicular magnetic recording medium (CoNi / Pt medium) including a magnetic layer in which a 95 at% Co-5 at% Ni layer and a Pt layer are laminated, and {90 mol% (95 at% Co-5 at% Ni)- 10 mol% SiO ₂ } A perpendicular magnetic recording medium (CoNi-SiO) comprising a magnetic layer in which a multilayer of a Pt layer and a Pt layer is laminated ₂ FIG. 6 is a diagram for explaining recording / reproduction characteristics (SN characteristics) of a (/ Pt medium).
FIG. 7 shows a perpendicular magnetic recording medium (CoRu / Pt medium) having a magnetic layer in which a 95 at% Co-5% Ru layer and a Pt layer are laminated, and {99.8 mol% (95 at% Co-5 at% Ru). ) -0.2 mol% O ₂ } Perpendicular magnetic recording medium (CoRuO) comprising a magnetic layer in which multiple layers and Pt layers are laminated ₂ FIG. 6 is a diagram for explaining recording / reproduction characteristics (SN characteristics) of a (/ Pt medium).
FIG. 8 is a diagram for explaining the effect of the crystal orientation control layer provided in the perpendicular magnetic recording medium of the present invention.
FIG. 9 is a diagram for explaining the effect of adsorbing oxygen on the surface of the underlayer.
FIG. 10 is a diagram for explaining reproduction output which is a recording / reproduction characteristic of a conventional product and a product of the present invention.
FIG. 11 is a diagram for explaining medium noise which is a recording / reproducing characteristic of a conventional product and a product of the present invention.
FIG. 12 is a diagram for explaining SNR which is a recording / reproducing characteristic of a conventional product and a product of the present invention.
FIG. 13 shows Co—SiO constituting a magnetic layer. ₂ It is a plane TEM image for demonstrating the mode of the magnetic particle diameter in a layer, and the nonmagnetic grain boundary width.
FIG. 14 is a diagram for explaining a change in magnetic characteristics when the thickness of a Pt layer is changed.
FIG. 15 is a diagram for explaining changes in magnetic characteristics when the film thickness of a NiFeNbB layer is changed.
FIG. 16 is a diagram for explaining changes in magnetic characteristics when the thickness of a Pd layer is changed.
FIG. 17: Co-SiO ₂ It is a figure for demonstrating the effect of the Ru base layer on the magnetic characteristic of the magnetic layer of a / Pd multilayer laminated structure.
18 shows the Co—SiO of the present invention described in Example 4. FIG. ₂ / Pt multilayer magnetic layered perpendicular magnetic recording medium and Co-SiO2 of Example 5 ₂ FIG. 5 is a diagram for explaining recording / reproduction characteristics with a perpendicular magnetic recording medium including a magnetic layer having a / Pd multilayer stack structure.
FIG. 19 shows 91 mol% Co-9 mol% SiO. ₂ / 95 mol% Pt-5 mol% SiO ₂ Magnetic layer composed of multilayer laminated film, and 94 mol% Co-6 mol% SiO ₂ / 95 mol% Pt-5 mol% SiO ₂ Magnetic layer composed of multilayer laminated film, and 91 mol% Co-9 mol% SiO ₂ FIG. 6 is a diagram for explaining the dependence of each Hc of a perpendicular magnetic recording medium including a magnetic layer formed of a / Pt multilayer film on the film thickness of a second magnetic layer.
FIG. 20 is a diagram for explaining the dependency of the inclination α near the Hc of each of the three types of perpendicular magnetic recording media described in FIG. 19 on the thickness of the second magnetic layer.
FIG. 21: 91 mol% Co-9 mol% SiO ₂ / 95 mol% Pt-5 mol% SiO ₂ A medium having a magnetic layer composed of a multilayer film, and 91 mol% Co-9 mol% SiO ₂ FIG. 6 is a diagram for explaining the dependence of the magnetic anisotropy constant Ku on the thickness of the second magnetic layer in each of the perpendicular magnetic recording media including the magnetic layer formed of the / Pt multilayer laminated film.
FIG. 22 shows 18 to 38% by volume of SiO in the Co layer. ₂ Add Co-SiO ₂ FIG. 5 is a diagram summarizing results of measuring Hc of a medium including a magnetic layer made of a / Pt multilayer laminated film.
FIG. 23 shows SiO into a Pt layer of Hc. ₂ It is a figure for demonstrating the addition effect.
[Explanation of symbols]
1 Substrate
2 backing layer
3 First orientation control layer
4 Second orientation control layer
5 Underlayer
6 Magnetic layer
6a First magnetic layer
6b Second magnetic layer
7 Protective layer

Claims (18)

A perpendicular magnetic recording medium comprising a magnetic layer on a nonmagnetic substrate,
The magnetic layer is formed by alternately laminating a Co layer as a first magnetic layer and a Pt layer or a Pd layer as a second magnetic layer, and the first magnetic layer or the second magnetic layer. A perpendicular magnetic recording medium, wherein at least one of Ru, Ta, Nb, Mo, Mn, Cr, Si, and Ni is added to at least one of the magnetic layers. The perpendicular magnetic recording medium according to claim 1, wherein the addition amount is in a concentration range of 1 to 15 mol%. The second magnetic layer is a Pt layer, Si oxide is added to both the first and second magnetic layers, and the amount of Si oxide added to the Co layer as the first magnetic layer is 3. The perpendicular magnetic recording medium according to claim 2, wherein the Si oxide addition amount in the Pt layer as the second magnetic layer is 5 to 11 mol%, and 1 to 8 mol%. 4. The method according to claim 1, wherein each of the first magnetic layer and the second magnetic layer has a thickness of 0.2 to 0.8 nm and 0.05 to 1.2 nm. A perpendicular magnetic recording medium according to claim 1. 5. The perpendicular magnetic recording medium according to claim 1, further comprising an underlayer between the magnetic layer and the substrate, wherein the magnetic layer is provided immediately above the underlayer. 6. The perpendicular magnetic recording medium according to claim 5, wherein the underlayer is any one of a Pt film, a Pd film, a Ru film, or a Pt / Pd laminated film. 7. The perpendicular magnetic recording medium according to claim 5, wherein the underlayer has a thickness of 1 to 20 nm. The perpendicular magnetic recording medium according to claim 5, further comprising an orientation control layer for controlling crystal orientation of the underlayer between the substrate and the underlayer. The orientation control layer is formed by laminating a first orientation control layer and a second orientation control layer, and the composition of the second orientation control layer is such that the underlayer is c-axis crystal oriented. The perpendicular magnetic recording medium according to claim 8, wherein the perpendicular magnetic recording medium is set as follows. 10. The perpendicular magnetic recording according to claim 9, wherein the first orientation control layer is a Ta layer, and the second orientation control layer is any one of a NiFeCr layer, a NiFeNbB layer, and a NiFeSi layer. Medium. 11. The perpendicular magnetic recording according to claim 9, wherein the thickness of the first orientation control layer is set in a range of 1 to 10 nm, and the thickness of the second orientation control layer is set in a range of 5 to 20 nm. Medium. 12. The perpendicular magnetic recording medium according to claim 9, wherein a soft magnetic backing layer is provided between the nonmagnetic substrate and the first orientation control layer. 13. The perpendicular magnetic recording medium according to claim 12, wherein the backing layer has a CoZrNb or CoZrTa alloy composition and has a thickness of 50 to 400 nm. A method for manufacturing a perpendicular magnetic recording medium, comprising:
A step of forming a magnetic layer by alternately laminating a Co layer as a first magnetic layer and a Pt layer or a Pd layer as a second magnetic layer on a nonmagnetic substrate;
The magnetic layer is formed using a target to which at least one element or oxide of Ru, Ta, Nb, Mo, Mn, Cr, Si, and Ni is added in a concentration range of 1 to 15 mol%. A method of manufacturing a perpendicular magnetic recording medium, which is performed by sputtering. 15. The perpendicular magnetism according to claim 14, wherein the step of forming the magnetic layer is performed using a sputtering gas to which oxygen gas is added in a concentration range of 0.05 to 0.5% by mass flow ratio. A method for manufacturing a recording medium. Prior to the formation of the magnetic layer, a step of sputter-depositing a base layer of any one of a Pt film, a Pd film, a Ru film, or a Pt / Pd laminated film on the substrate is provided. Item 16. A method for producing a perpendicular magnetic recording medium according to Item 14 or 15. In sputter deposition of the magnetic layer and sputter deposition of the underlayer, any one of a mixed gas of Kr, Xe, Kr and Ar or a mixed gas of Xe and Ar is used as a sputtering gas. The method of manufacturing a perpendicular magnetic recording medium according to claim 16. After the formation of the underlayer and before the formation of the magnetic layer, the surface of the underlayer is placed in Ar gas having a gas pressure of 0.1 to 10 Pa mixed with oxygen having a mass flow rate ratio of 1 to 10%. 17. The method of manufacturing a perpendicular magnetic recording medium according to claim 16, further comprising a step of adsorbing oxygen on the surface of the underlayer by exposure for 20 seconds.

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