【０００１】
【発明の属する技術分野】
本発明は１平方センチメートルあたり１５ギガビット以上の超高密度記録に適した垂直磁気記録媒体およびその製造方法ならびにそれを用いた磁気記憶装置に関する。
【０００２】
【従来の技術】
近年、コンピュータが扱う情報量が増大し、補助記憶装置の大容量化が一段と求められている。現在実用化されている磁気ディスク装置は面内記録方式を採用しており、その面記録密度は４．７ギガビット／平方センチメートルに到達している。しかし、この面内記録方式では記録磁化が互いに逆向きで隣接するため、高密度化が進むにつれて記録層の保磁力を高める必要がある。また、高密度化に伴って記録ビットは小さくなり、高感度な再生ヘッドを使用するため、媒体ノイズの低減も必須である。それには記録層の膜厚を薄くする必要があり、同時に熱揺らぎの影響によって記録磁化が減衰するといった問題が発生する。
【０００３】
一方、垂直記録方式では面内記録方式に比べて高密度領域での反磁界が小さいため、面内記録方式に比べて高密度化に有利であると言われている。垂直記録方式には、単層の垂直磁化膜を用いる方式と、軟磁性裏打ち層と垂直磁化膜を積層する方式がある。前者は記録用に薄膜リングヘッドが用いられるが、後者は単磁極型の記録ヘッドと組み合わせることにより急峻な垂直磁界勾配が得られ、高保磁力を有する媒体への記録も容易となる。
【０００４】
この垂直記録媒体においても、媒体ノイズの低減は必須である。それには磁性結晶粒の微細化、粒間相互作用の低減等が必要であり、これまでに記録層に添加する元素や媒体の膜構造の最適化によってノイズ低減が進められてきた。例えば特開２０００−３２２７２６や特開２０００−４０２１６に記載されている酸化物を添加した記録層は、明瞭な結晶粒界を形成し易く、粒間相互作用の低減に有利であると言われている。
【０００５】
【発明が解決しようとする課題】
１平方センチメートルあたり１５ギガビット以上の高密度記録が可能な垂直記録媒体には、更なる低ノイズ化と耐熱減磁特性向上が必要とされる。このためには、軟磁性層と記録層とを磁気的に分断する中間層の膜厚を薄くすると同時に、垂直記録層の磁性結晶粒を微細化し、かつ垂直磁気異方性を増大させるとともに、粒間相互作用を低減する必要がある。しかしながら、粒間相互作用低減を目的に記録層に酸化物を添加した媒体では、中間層の薄膜化が困難であった。
【０００６】
発明者らはこれまでに、中間層として酸素含有層上に金属層を積層することで、島状に孤立した構造からなる金属層を形成させ、この孤立した複数の島構造を核として記録層の結晶粒を成長させることにより、記録層の結晶粒径を微細化し、磁気的に孤立し、さらに均一化させ、同時に、中間層を薄膜化することによって媒体ノイズが小さく、記録効率が高く、しかも記録分解能が高い垂直記録媒体を得ることを検討してきた。
【０００７】
これまで検討を行ってきた、酸素含有層上に金属層を形成し、さらに貴金属元素にＢまたはＳｉを添加して酸素を含有させた中間層においては、磁性結晶粒の孤立化、微細化、均一化は改善されるものの、高密度記録を達成するのに十分な保磁力、角形比と低ノイズ性を同時に得ることができなかった。
【０００８】
本発明の第１の目的は、１平方センチメートルあたり１５ギガビット以上の高密度記録を可能とする垂直記録層を有し、かつ、記録情報を長期間保持できる垂直磁気記録媒体を提供することにある。
【０００９】
本発明の第２の目的は、この垂直磁気記録媒体の性能を充分に活かし、１平方センチメートルあたり１５ギガビット以上の面記録密度を有する磁気記憶装置を提供することにある。
【００１０】
【課題を解決するための手段】
上記課題は、基板上に軟磁性層と中間層と垂直記録層と保護層を有する構造の磁気記録媒体において、基板に近い側から第１の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とした金属層であり、第２の中間層は酸素含有層であり、第３の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とした金属層であり、第４の中間層はＣｏ、Ｃｒ、Ｒｕ、Ｔｉより選ばれた少なくとも１種の元素を主成分とする金属層であり、前記垂直記録層はＣｏを主成分とし、かつ酸素を含有することによって達成される。
【００１１】
本発明者らは、第１中間層によって垂直配向を制御し、第２中間層の酸素含有層と第３中間層の金属層で島状に孤立した構造（凸状の構造）を形成し、この凸形状を核としてさらに六方稠密構造の第４中間層を形成した四層構造中間層を用いて記録層に酸素を含有することで、記録層の保磁力、角形比が向上、媒体ノイズが低減、耐熱減磁特性が向上することを見出した。
【００１２】
上記第４の中間層は六方稠密構造の材料を用い、かつ第３中間層と異なる材料を用いることが好ましい。上記の第１中間層から第３中間層までで垂直配向性、結晶粒径を制御することができるが、より大きな保磁力、角形比を得るにはさらにもう一層の中間層を形成する必要がある。
【００１３】
第３中間層上に直接垂直記録層を形成した場合、酸素含有層が表面に露出している部分では垂直配向性が劣化した結晶粒や粒界偏析が促進されるものと考えられる。酸素含有層上に直接記録層を形成した場合、垂直配向しない結晶粒が数多く存在することとなり、垂直磁気異方性を著しく劣化させるため好ましくない。また、これまでに検討を行ってきたＰｄ、Ｐｔ、Ａｕ、Ａｇのような貴金属元素にＢまたはＳｉを添加し、さらに酸素を含有させた第４中間層では、ある程度の保磁力は得られるものの、十分な角形比までは得られなかった。
【００１４】
本発明においては、六方稠密構造の第４中間層を適用することにより、３００ｋＡ／ｍ以上の保磁力と０．９５以上の角形比が同時に得られることを見出した。この第４中間層に第３中間層と同一の材料を用いた場合、第３中間層の膜厚を増大させて第４中間層を形成しない場合とほぼ同等の特性を示し、３００ｋＡ／ｍ以上の保磁力と０．９５以上の角形比が得られないため好ましくない。また、Ｂ、Ｏ等を添加して第３中間層と材料を区別化した第４中間層としても、保磁力は僅かに増大するが、角形比がほとんど増加しないため効果は小さい。この第４中間層としてはＣｏ、Ｃｒ、Ｒｕ、Ｔｉ等を主成分とし、かつ六法稠密構造となる組成比とすることが好ましい。
【００１５】
上記第１の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とすることが好ましい。本願発明者らが行った検討によると、第１中間層の配向が記録層の配向に大きく影響することがわかった。すなわち、第１中間層で面心立方構造の（１１１）面、もしくは六方稠密構造の（０００１）面を基板と平行になるように配向させると、記録層の（０００１）配向が得られることがわかった。
【００１６】
この第１中間層を非結晶、もしくは体心立方構造の中間層とした場合、記録層は垂直配向せず、保磁力は１００ｋＡ／ｍ以下、角形比は０．３以下となるので好ましくない。この第１中間層の材料としては、Ｐｄ、Ａｕ、Ａｇ、Ｒｈ、Ｐｔ、Ｒｕ、Ｔｉ等を主成分とすることが好ましいが、他の面心立方構造、六方稠密構造、あるいはＬ１０型構造のような規則相を持つ材料を用いてもよい。その場合の膜厚は０．５ｎｍ以上あれば記録層の垂直配向が得られる。
【００１７】
上記第２の中間層は、酸素含有層とすることが好ましい。この酸素含有層は表面エネルギが小さく、この表面に相対的に表面エネルギの大きな金属層を形成すると、金属層が薄い領域において金属層が酸素含有層の表面を覆い尽くすことはなく、島状に孤立した構造を形成することができる。さらに金属膜の材料、膜厚、および形成温度によってこの構造を制御することが可能である。この酸素含有層はＭｇＯ、ＳｉＯ２、Ａｌ２Ｏ３、ＴｉＯ、ＮｉＯ等であることが好ましい。
【００１８】
上記第３の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とすることが好ましい。第３中間層の配向は第１中間層によって決まるため、その配向性を維持する材料を用いることが好ましい。特に第１中間層と同じ材料とすると最も保磁力が高くなるが、他の面心立方構造あるいは六方稠密構造の材料を用いても高い保磁力が得られる。この第３中間層は酸素含有層上に形成することで島状となり、その形状は材料の融点、膜厚および基板温度によって決定される。
【００１９】
上記までの中間層は、垂直記録層としてＣｏを主成分とし、かつ酸素を含有することでその効果が大きくなる。酸化物と金属は固溶しないため、記録層に酸化物、もしくは酸素を添加して酸化物を形成した場合、結晶粒界に酸化物が析出しやすくなる。特に中間層によって形状的に粒界を形成しやすい構造となっているため、粒間相互作用が十分低減された記録層を形成することが可能となる。この場合の記録層を形成する基板温度は１５０℃以下とする必要がある。基板温度が高い場合、結晶粒内にも酸化物や酸素が存在することとなり、垂直磁気異方性が大幅に劣化するので好ましくない。基板温度を１００℃以下、さらには７０℃以下とすると、ＣｏＣｒＰｔと酸化物とが完全に分離するのでより好ましい。
【００２０】
さらに、本発明の垂直磁気記録媒体と、該磁気記録媒体を記録方向に駆動する駆動部と、記録部と再生部からなる磁気ヘッドと、該磁気ヘッドを前記磁気記録媒体に対して相対的に運動させる手段と、前記磁気ヘッドに対する入力信号および出力信号を波形処理する記録再生信号処理手段とを含む磁気記憶装置において、前記磁気ヘッドの再生部を磁気抵抗効果型の素子で構成し、記録ヘッドを単磁極型とすることによって、１平方センチメートルあたり１５ギガビット以上の記録密度を有する磁気記憶装置を達成することができる。
【００２１】
【発明の実施の形態】
（実施例１）
以下に、本実施例の磁気記録媒体の作製方法を述べる。図１は本発明の一実施例である磁気記録媒体の構成を模式的に示す断面図である。
【００２２】
外径６５ｍｍφのガラス基板１０に、Ｆｅ−８ａｔ％Ｔａ−１２ａｔ％Ｃ軟磁性層１１、１１’を４００ｎｍ形成した後、基板温度を一旦４４０℃まで上昇させて２８０℃まで冷却し、Ｐｄ第１中間層１２、１２’を１．５ｎｍ形成した。ついで、ＭｇＯ第２中間層１３、１３’を１ｎｍ形成し、Ｐｄ第３中間層１４、１４’を１．５ｎｍ形成し、Ｒｕ第４中間層１５、１５’を３ｎｍ形成した。さらに、基板温度が１５０℃以下になるまで冷却してから、基板の前を円周方向に毎分１００回転の速度で回転するマグネトロンカソードを用い、Ｃｏ−１３ａｔ％Ｃｒ−２０ａｔ％Ｐｔ合金ターゲットとＳｉＯ２ターゲットを同時に放電させ、ＣｏＣｒＰｔ合金中にＳｉＯ２が１５ｍｏｌ％含まれるようにスパッタを行って記録層１６、１６’を２０ｎｍ成膜した。最後に、保護層１７、１７’としてＣを５ｎｍ形成した。
【００２３】
本実施例ではＭｇＯとＳｉＯ２を形成する場合にＲＦスパッタリング法を用い、それ以外の場合にはＤＣマグネトロンスパッタリング法にて膜の形成を行った。また、スパッタガスにはアルゴンを用い、ＤＣスパッタを行う場合には０．５Ｐａ、ＭｇＯと記録層形成時のＲＦスパッタを行う場合には２．０Ｐａの圧力に設定した。ここで、元素の前に付した数字は各元素の濃度を示す。
【００２４】
また比較例１として、中間層１５、１５’の代わりに、アルゴンに３％の酸素を添加した混合ガスを用いて３ｎｍのＰｄ−１０ａｔ％Ｂ中間層を形成した媒体を作製した。作製条件は第４中間層以外は全て同じであり、本実施例１の媒体にはＲｕ第４中間層を用いたのに対し、比較例１の媒体にはＰｄＢ第４中間層を用いたところが相違点である。
【００２５】
表１に本実施例１と比較例１の静磁気特性を示す。静磁気特性の測定にはカー効果型磁力計を用い、磁界をサンプルの膜面垂直に印加しながらカー回転角を検出してカーループを測定した。磁界の掃印は一定速度でプラス１７５０ｋＡ／ｍからマイナス１７５０ｋＡ／ｍ、そしてマイナス１７５０ｋＡ／ｍからプラス１７５０ｋＡ／ｍまでを６４秒間で行った。表１に示すように、本実施例の媒体は比較例の媒体よりも保磁力、角形比が高い結果が得られた。
【００２６】
【表１】
表２に実施例１と比較例１のスピンスタンドにおけるＲ／Ｗ特性の評価結果を示す。この評価に用いたヘッドはシールドギャップ長６２ｎｍ、トラック幅１２０ｎｍの巨大磁気抵抗効果を利用した再生素子と、トラック幅１５０ｎｍの単磁極型書き込み素子からなる複合型ヘッドである。周速１０ｍ／ｓ、スキュー角０度、磁気スペーシング約１５ｎｍの条件で、再生出力、媒体ノイズと熱減磁特性を測定した。
【００２７】
出力分解能は２３６２０ｆｒ／ｍｍの線記録密度における再生出力と１９７０ｆｒ／ｍｍの線記録密度における再生出力の比であり、媒体ノイズは２３６２０ｆｒ／ｍｍの線記録密度におけるノイズとした。熱減磁特性は、３９４０ｆｒ／ｍｍの信号を記録してから１０００秒経過後の再生出力の変化量とした。これらの値は本実施例の値を１として、比較例１の値は相対値で示した。
【００２８】
【表２】
表２のように、本実施例のほうが出力分解能特性は高く、本発明によって角形比が向上した効果と考えられる。媒体ノイズは本実施例のほうが僅かながら低いことから、粒界偏析も促進されやすいと考えられる。また、再生出力の変化量は本実施例の媒体のほうが小さく、本発明の媒体は耐熱減磁特性にも優れていることがわかった。
【００２９】
ここで、第４中間層の効果について調べた。上記実施例１と同様な構造の媒体を作製し、第４中間層の膜厚を変えた場合の静磁気特性を図２に示す。第４中間層を形成することによって高い角形比が得られていることから、Ｒｕ第４中間層は垂直配向を高める効果があると考えられる。保磁力はＲｕ膜厚が０．５ｎｍで３００ｋＡ／ｍを越えることから、第４中間層には保磁力を増大する効果もあることがわかった。
【００３０】
表３に第４中間層の材料を変えた場合の静磁気特性を示す。大きな保磁力、角形比が得られたのは六方稠密構造を持つ材料であり、他の構造を持つ材料では高い保磁力、角形比を両立できるものはなかった。面心立方構造を持つ材料では保磁力はある程度高くなるが、角形比が０．９以下となる。これは、面心立方構造と六方稠密構造は二次元格子の原子配列は同じだが、記録層が六方稠密構造であるため、面心立方構造の中間層を用いると結晶構造の違いにより初期層で配向の乱れた結晶粒が生成されるため、角形比が高くならないと考えられる。
【００３１】
【表３】
さらに、第１中間層の効果について調べた。上記実施例１と同様な構造の媒体を作製し、第１中間層の材料を変えた場合の静磁気特性を表４に示す。大きな保磁力、角形比が得られたのは面心立方構造あるいは六方稠密構造を持つ材料を用いた場合であり、体心立方構造を持つ材料もしくはアモルファスな材料を用いた場合では保磁力、角形比ともに低い値しか得られなかった。
【００３２】
【表４】
表５に第１中間層の材料を変えた場合の媒体について、Ｘ線回折装置によって記録層の（０００１）面の回折強度を調べた結果を示す。この場合の回折強度はＰｄ中間層の場合を１とし、他の中間層の値は相対値で示した。
【００３３】
【表５】
低い保磁力しか得られなかった媒体では、（０００１）面がほとんど配向せず、アモルファスな材料は回折ピークが観察できなかった。大きな保磁力が得られた材料は面心立方構造と六方稠密構造であった。
【００３４】
次に、Ｐｄ第１中間層の膜厚を変えた場合の静磁気特性を図３に示す。Ｐｄが０．５ｎｍでも形成されていれば高保磁力、高角形比となり、どの膜厚においても角形比は高い値を維持している。また、Ｐｄ膜厚が５ｎｍの媒体について、実施例１と同様な作製方法で第１中間層まで形成した媒体を作成し、Ｘ線回折装置によってＰｄの配向を調べた。このときのＰｄは（１１１）配向しており、それ以外の回折ピークは見られなかった。このことから、第１中間層が（１１１）配向を維持していれば記録層の垂直配向が得られるとわかった。
【００３５】
次に、第２中間層の効果について調べた。表６に上記実施例１と同様な構造の媒体を作製し、第２中間層の材料を変えた場合の静磁気特性を示す。第２中間層を他の酸化物にした場合でも、実施例１と同等の静磁気特性が得られていることから、第２中間層はＭｇＯに限らず酸素含有層であればよいことがわかった。
【００３６】
【表６】
次に第３中間層の効果について調べた。表７に上記実施例１と同様な構造の媒体を作製し、第３中間層の材料を変えた場合の静磁気特性を示す。大きな保磁力、角形比が得られたのは面心立方構造あるいは六方稠密構造を持つ材料を用いた場合であり、体心立方構造もしくはアモルファスな材料を用いた場合では保磁力、角形比ともに低い値しか得られなかった。第１中間層で最稠密面である面心立方構造の（１１１）面あるいは六方稠密構造の（０００１）面が配向しているため、第３中間層も同じ原子配列をする材料を用いて同様な配向をさせる必要があるとわかった。
【００３７】
【表７】
次に、図４に第３中間層の膜厚を変えた場合の静磁気特性を示す。保磁力は０．５ｎｍ以上２．５ｎｍ以下で大きな値が得られ、Ｐｄ膜厚１．５ｎｍで最大となった。これらの媒体のＰｄ膜厚が１．５ｎｍ、３ｎｍの試料について断面構造を調べた。
【００３８】
図５に本実施例の媒体の断面構造を約１２５万倍の高倍率で観察した透過電子顕微鏡像を模式的に書き写した図を示す。図において、５０はＰｄ第１中間層、５１はＭｇＯ第２中間層、５２はＰｄ第３中間層、５３はＲｕ第４中間層、５４は記録層である。酸素を含有するＭｇＯ第２中間層５１は明るいコントラストで明瞭に観察される。島状金属層の役割を担うＰｄ第３中間層５２はＲｕ第４中間層５３とのコントラスト差が小さいことから明瞭に認識できない。記録層５４はＳｉＯ２によって粒界が明瞭に認識できる。
【００３９】
図５（ａ）に示すＰｄ第３中間層膜厚１．５ｎｍの場合では、ＭｇＯ第２中間層５１の表面から記録層５４の粒界までの平均膜厚が２．９ｎｍであった。この場合の第３中間層５２と第４中間層５３の膜厚の合計は４．５ｎｍであり、記録層５４の粒界が形成された部分は中間層５２および５３の膜厚が薄くなっていることがわかる。これは中間層に凹凸が付与された状態であることを示しており、凹部には粒界、凸部には結晶粒が形成されることがわかった。
【００４０】
一方、図５の（ｂ）に示すＰｄ第３中間層膜厚が３ｎｍの場合では、ＭｇＯ第２中間層５１の表面から記録層５４の粒界までの平均膜厚が５．４ｎｍであった。これはＰｄがほぼ連続膜となっており、凹凸形状がほとんどつかないことを示している。また、このことは記録層表面にも影響しており、膜厚を１．５ｎｍとした図５（ａ）に示すＰｄ第３中間層５２のほうが記録層表面の凹凸が大きく、第３中間層５２の凹凸が影響していると考えられる。
【００４１】
次に、図４に示す媒体について、ＭｇＯ中間層から記録層の粒界までの平均膜厚を調べた結果を図６に示す。Ｐｄ膜厚が薄い領域では平均膜厚はあまり増加しておらず、Ｐｄ膜厚が１．５ｎｍを超えたあたりから急激に増加することがわかる。図４の結果と比較すると、高い保磁力が得られる平均膜厚は０．５ｎｍ以上４．５ｎｍ以下であった。
【００４２】
次に、垂直記録層の組成について調べた。図７に上記実施例１と同様な構造の媒体について、ＳｉＯ２添加濃度を変えた場合の静磁気特性を示す。３００ｋＡ／ｍ以上の高い保磁力が得られるのはＳｉＯ２の添加濃度を１０ｍｏｌ％以上２０ｍｏｌ％以下とした場合であり、角形比はＳｉＯ２の添加濃度を２０ｍｏｌ％以上とすると劣化する。ＳｉＯ２濃度が低い領域で保磁力が低下するのは、形状的に粒界を形成しやすい中間層であっても粒界偏析する材料が不足するためと考えられる。逆にＳｉＯ２濃度が高い場合に保磁力、角型比が低下するのは、粒界偏析する材料が多すぎるために結晶粒サイズが小さくなりすぎたためと考えられる。
（実施例２）
図８は本発明の第２の実施例である磁気記録媒体の構成を模式的に示す断面図である。以下に、本実施例の磁気記録媒体の作製方法を述べる。
【００４３】
本実施例の垂直磁気記録媒体は第４中間層８５、８５’までは実施例１と同様の膜構成および同じプロセス条件で作製し、記録層８６、８６’についてはアルゴンガスに０．５％の酸素を添加したものをスパッタガスとして用い、ターゲットにはＣｏ−１３ａｔ％Ｃｒ−１４ａｔ％Ｐｔを用いて２０ｎｍ形成した。最後に、保護層８７、８７’としてＣを５ｎｍ形成した。
【００４４】
また比較例２として、第４中間層８５、８５’に、Ｒｕの代わりにＰｄ−１０ａｔ％Ｂ中間層を３％の酸素をアルゴンに添加した混合ガスを用いて３ｎｍ形成した媒体を作製した。作製条件は第４中間層以外、全て同じであり、本実施例２の媒体にはＲｕ第４中間層を用いたのに対し、比較例２の媒体にはＰｄＢ第４中間層を用いたところが相違点である。
【００４５】
表８に本実施例媒体と比較例２の静磁気特性を示す。測定条件は上記実施例１と同じとした。保磁力、角型比ともに実施例２のほうが高く、本発明中間層は記録層に酸化物を添加した場合だけでなく、記録層形成時に酸素を添加した場合にも適用できることがわかった。
【００４６】
【表８】
表９に本実施例２の媒体と比較例２のＲ／Ｗ特性を示す。測定条件は上記実施例１と同じとし、実施例２の値を１として比較例２の値は相対値で示した。本実施例のほうが出力分解能特性は高く、角型比が向上した効果と考える。媒体ノイズは本実施例のほうが低く、粒界偏析も促進されていると考える。また、再生出力の変化量は本実施例媒体のほうが小さく、本発明の媒体は耐熱減磁特性にも優れていることがわかった。酸素導入スパッタによってＣｏもしくはＣｒが酸化物となり、結晶粒界に偏析して粒間相互作用が低減された効果と考えられる。
【００４７】
【表９】
次に、上記実施例２と同様な構造の媒体において、第１中間層を形成する温度を変えた場合の静磁気特性を図９に示す。このときの基板温度は、軟磁性層加熱後の冷却時間を変えて中間層形成時の基板温度を変え、記録層形成時の基板温度が同じになるように記録層形成前に冷却をした。
【００４８】
保磁力は基板温度を２００℃以上とすると３００ｋＡ／ｍ以上となるが、角型比は基板温度を３５０℃以上とすると急激に劣化する。これは中間層を形成する温度によってＭｇＯ上に形成された中間層の凹凸形状が変化することが配向に影響すると考えられ、３５０℃以上の高温領域で急激に劣化するのは、隣接する層との反応が起こって配向が劣化するためと考えられる。
【００４９】
図１０に、記録層形成時の基板温度を変えた場合の静磁気特性を示す。記録層形成時の基板温度が１５０℃を超えると保磁力は３００ｋＡ／ｍ以下となり、基板温度が低くなるほど保磁力は向上する。記録層を形成するときの温度が高い場合、酸化物が結晶粒内に含まれたり、必要以上にＣｏの酸化が進むことによって磁気異方性が劣化すると考えられる。
（実施例３）
次に、上記実施例２と同様の膜構成の媒体において、記録層に人工格子膜を用いた実施例３を作製した。人工格子膜の形成は、毎分１００回転の速度で回転するマグネトロンカソードを用い、Ｃｏ−１０ａｔ％ＢターゲットとＰｄターゲットを同時に放電させることにより行った。その場合の膜厚はＣｏＢを０．３ｎｍ、Ｐｄを１．２ｎｍとし、それぞれ１５層ずつ積層した。スパッタガスにはアルゴンに酸素を１％添加した混合ガスを用い、ガス圧は７Ｐａとした。
【００５０】
表１０に実施例３と比較例２の静磁気特性を示す。実施例３の保磁力は５３０ｋＡ／ｍと高く、角形比は１．０であった。また、表１１に実施例３と比較例２のＲ／Ｗ特性を示す。測定条件は上記実施例１と同じとし、実施例３の値を１として比較例２の値は相対値で示した。本実施例３のほうが出力分解能特性は高く、媒体ノイズは本実施例のほうが低い。また、本実施例は再生出力の変化がほとんど無く、本発明の媒体は耐熱減磁特性にも優れていることがわかった。このことから、本発明の中間層は記録層を人工格子膜にした場合でも効果があると確認できた。
【００５１】
【表１０】
【表１１】
（実施例４）
前記実施例の磁気記録媒体は、図１１に一例を示すような磁気記憶装置に組み込むことによって性能を充分に発揮できる。この磁気記憶装置の上面図を図１１（ａ）に、そのＡＡ’線断面図を図１１（ｂ）に略示する。
【００５２】
磁気記録媒体１１０は、磁気記録媒体駆動部１１１に連結する保持具によって保持され、磁気記録媒体１１０のそれぞれの面に対向して磁気ヘッド１１２が配置される。磁気ヘッド１１２は磁気的浮上高さ０．０１５μｍ以下で安定低浮上させ、さらに０．０３μｍ以下のヘッド位置決め精度で所望のトラックに磁気ヘッド駆動部１１３により駆動される。
【００５３】
磁気ヘッド１１２によって再生した信号は、記録再生信号処理系１１４によって波形処理される。記録再生信号処理系１１４は増幅器、アナログ等化器、ＡＤコンバータ、ディジタル等化器、最尤復号器等で構成されている。磁気抵抗効果を利用したヘッドの再生波形は、ヘッドの特性により正と負の大きさが非対称となったり、記録再生系の周波数特性の影響を受けたりして、記録した信号とは異なった信号に読み誤られることがある。アナログ等化器は再生波形を整えて、これを修復する機能を有する。この修復された波形をＡＤコンバータを通してディジタル変換し、ディジタル等化器によってさらに波形を整える。最後にこの修復された信号を最尤復号器によって、最も確からしいデータに復調する。以上の構成の再生信号処理系によって、極めて低いエラーレートで信号の記録再生が行われる。なお、等化器や最尤復号器は既存のものを用いても構わない。
【００５４】
以上の装置構成にすることによって、１平方センチメートルあたりの記録密度を１５ギガビット以上に対応することができ、従来の磁気記憶装置に比べ３倍以上の記憶容量を持った高密度磁気記憶装置を実現することができた。また、記録再生信号処理系から最尤復号器を取り除き、従来の波形弁別回路に変えた場合にも従来に比べて２倍以上の記憶容量を持った磁気記憶装置を実現することができた。
【００５５】
【発明の効果】
基板上に軟磁性層と中間層と垂直記録層と保護層を有する構造の磁気記録媒体において、基板に近い側から第１の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とした金属層であり、第２の中間層は酸素含有層であり、第３の中間層はＰｄ、Ｐｔ、Ａｕ、Ａｇ、Ｒｈ、Ｒｕ、Ｔｉよりなる群から選ばれた少なくとも１種の元素を主成分とした金属層であり、第４の中間層はＣｏ、Ｃｒ、Ｒｕ、Ｔｉより選ばれた少なくとも１種の元素を主成分とする金属層であり、前記垂直記録層はＣｏを主成分とし、かつ酸素を含有することによって、高保磁力、高角形比を有しながら低ノイズであり、かつ熱揺らぎの影響が小さな垂直記録媒体を実現できる。
【００５６】
さらに、この磁気記録媒体と磁気抵抗効果を利用した再生専用の素子を有する磁気ヘッドとを組み合わせることによって、１平方センチメートルあたり１５ギガビット以上の記録密度を有する磁気記憶装置が得られる。
【図面の簡単な説明】
【図１】本発明の一実施例である垂直磁気記録媒体の断面模式図。
【図２】静磁気特性の第４中間層膜厚依存性を示す図。
【図３】静磁気特性の第１中間層膜厚依存性を示す図。
【図４】静磁気特性の第３中間層膜厚依存性を示す図。
【図５】本発明の一実施例である垂直磁気記録媒体の断面を透過型電子顕微鏡で観察したときの断面模写図。
【図６】ＭｇＯ中間層から記録層の粒界までの平均膜厚のＰｄ膜厚依存性を示す図。
【図７】静磁気特性の記録層へのＳｉＯ２濃度依存性を示す図。
【図８】本発明の一実施例である磁気記録媒体の断面模式図。
【図９】静磁気特性の中間層形成時の基板温度依存性を示す図。
【図１０】静磁気特性の記録層形成時の基板温度依存性を示す図。
【図１１】本発明の一実施例である磁気記憶装置の模式図。
【符号の説明】
１０…基板、１１，１１’…ＦｅＴａＣ軟磁性層、１２，１２’…Ｐｄ第１中間層、１３，１３’…ＭｇＯ第２中間層、１４，１４’…Ｐｄ第３中間層、１５，１５’…Ｒｕ第４中間層、１６，１６’…ＣｏＣｒＰｔＳｉＯ２記録層、１７，１７’…Ｃ保護層、５０…Ｐｄ第１中間層、５１…ＭｇＯ第２中間層、５２…Ｐｄ第３中間層、５３…Ｒｕ第４中間層、５４…記録層、８０…基板、８１，８１’…ＦｅＴａＣ軟磁性層、８２，８２’…Ｐｄ第１中間層、８３，８３’…ＭｇＯ第２中間層、８４，８４’…Ｐｄ第３中間層、８５，８５’…Ｒｕ第４中間層、８６，８６’…ＣｏＣｒＰｔＯ記録層、８７，８７’…Ｃ保護層、１１０…磁気記録媒体、１１１…磁気記録媒体駆動部、１１２…磁気ヘッド、１１３…磁気ヘッド駆動部、１１４…記録再生信号処理系。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a perpendicular magnetic recording medium suitable for ultra-high density recording of 15 gigabits per square centimeter or more, a method for manufacturing the same, and a magnetic storage device using the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the amount of information handled by a computer has increased, and a larger capacity of an auxiliary storage device has been demanded. The magnetic disk drive currently put to practical use employs an in-plane recording system, and its areal recording density has reached 4.7 gigabits / cm 2. However, in this in-plane recording method, since the recording magnetizations are adjacent to each other in opposite directions, it is necessary to increase the coercive force of the recording layer as the density increases. In addition, the recording bits become smaller as the density increases, and a high-sensitivity reproducing head is used. Therefore, it is essential to reduce the medium noise. For that purpose, it is necessary to reduce the thickness of the recording layer, and at the same time, there arises a problem that the recording magnetization is attenuated due to the influence of thermal fluctuation.
[0003]
On the other hand, the perpendicular recording method has a smaller demagnetizing field in the high-density region than the in-plane recording method, and is said to be advantageous in increasing the density as compared with the in-plane recording method. The perpendicular recording method includes a method using a single-layer perpendicular magnetization film and a method in which a soft magnetic underlayer and a perpendicular magnetization film are stacked. In the former case, a thin film ring head is used for recording. In the latter case, a steep vertical magnetic field gradient is obtained by combining with a single pole type recording head, and recording on a medium having a high coercive force becomes easy.
[0004]
Also in this perpendicular recording medium, reduction of medium noise is essential. For that purpose, miniaturization of magnetic crystal grains, reduction of interaction between grains, and the like are required, and noise reduction has been promoted by optimizing the elements added to the recording layer and the film structure of the medium. For example, a recording layer to which an oxide is added described in JP-A-2000-322726 or JP-A-2000-40216 easily forms a clear crystal grain boundary, and is said to be advantageous in reducing intergranular interaction. I have.
[0005]
[Problems to be solved by the invention]
Perpendicular recording media capable of high-density recording of 15 gigabits per square centimeter or more require further reduction in noise and improvement in heat-resistant demagnetization characteristics. To this end, while reducing the thickness of the intermediate layer that magnetically separates the soft magnetic layer and the recording layer, the magnetic crystal grains of the perpendicular recording layer are made finer, and the perpendicular magnetic anisotropy is increased. It is necessary to reduce intergranular interactions. However, in a medium in which an oxide is added to the recording layer for the purpose of reducing the intergranular interaction, it has been difficult to reduce the thickness of the intermediate layer.
[0006]
The inventors have previously formed a metal layer having an island-like isolated structure by laminating a metal layer on an oxygen-containing layer as an intermediate layer, and formed a recording layer using the isolated island structures as nuclei. By growing the crystal grains of the above, the crystal grain size of the recording layer is made finer, magnetically isolated and more uniform, and at the same time, by reducing the thickness of the intermediate layer, the medium noise is reduced, and the recording efficiency is increased. Moreover, it has been studied to obtain a perpendicular recording medium having a high recording resolution.
[0007]
In the intermediate layer, which has been studied so far, a metal layer is formed on an oxygen-containing layer, and B or Si is added to a noble metal element to contain oxygen, magnetic crystal grains are isolated, miniaturized, Although the uniformity is improved, a coercive force, a squareness ratio and a low noise property sufficient to achieve high density recording cannot be obtained at the same time.
[0008]
A first object of the present invention is to provide a perpendicular magnetic recording medium having a perpendicular recording layer capable of high-density recording of 15 gigabits or more per square centimeter and capable of holding recorded information for a long period of time.
[0009]
A second object of the present invention is to provide a magnetic storage device having a surface recording density of 15 gigabits per square centimeter or more by fully utilizing the performance of the perpendicular magnetic recording medium.
[0010]
[Means for Solving the Problems]
The above object is achieved by a magnetic recording medium having a structure in which a soft magnetic layer, an intermediate layer, a perpendicular recording layer, and a protective layer are provided on a substrate, wherein the first intermediate layer is formed of Pd, Pt, Au, Ag, Rh, A metal layer containing at least one element selected from the group consisting of Ru and Ti as a main component, a second intermediate layer being an oxygen-containing layer, and a third intermediate layer being composed of Pd, Pt, Au, and Ag. , Rh, Ru, Ti is a metal layer mainly composed of at least one element selected from the group consisting of, and the fourth intermediate layer is at least one element selected from Co, Cr, Ru, Ti. The perpendicular recording layer is achieved by containing Co as the main component and containing oxygen.
[0011]
The present inventors control the vertical alignment by the first intermediate layer, and form an island-like isolated structure (convex structure) between the oxygen-containing layer of the second intermediate layer and the metal layer of the third intermediate layer, By using the four-layer intermediate layer having the fourth intermediate layer of the hexagonal close-packed structure with the convex shape as a nucleus and containing oxygen in the recording layer, the coercive force and the squareness ratio of the recording layer are improved, and the medium noise is reduced. And improved heat-resistant demagnetization characteristics.
[0012]
It is preferable that the fourth intermediate layer uses a material having a hexagonal close-packed structure and a material different from that of the third intermediate layer. Although the vertical orientation and the crystal grain size can be controlled from the first intermediate layer to the third intermediate layer, it is necessary to form still another intermediate layer in order to obtain a larger coercive force and squareness ratio. is there.
[0013]
When a perpendicular recording layer is formed directly on the third intermediate layer, it is considered that crystal grains having deteriorated perpendicular orientation and grain boundary segregation are promoted in a portion where the oxygen-containing layer is exposed on the surface. If the recording layer is formed directly on the oxygen-containing layer, a large number of crystal grains that do not have a perpendicular orientation will be present, and the perpendicular magnetic anisotropy will be significantly deteriorated. Further, in the fourth intermediate layer in which B or Si is added to a noble metal element such as Pd, Pt, Au, or Ag, which has been studied, and oxygen is further contained, a certain coercive force can be obtained. , A sufficient squareness ratio could not be obtained.
[0014]
In the present invention, it has been found that a coercive force of 300 kA / m or more and a squareness of 0.95 or more can be simultaneously obtained by applying the fourth intermediate layer having a hexagonal close-packed structure. When the same material as that of the third intermediate layer is used for the fourth intermediate layer, the film thickness of the third intermediate layer is increased to exhibit substantially the same characteristics as when the fourth intermediate layer is not formed, and is equal to or more than 300 kA / m. And a squareness ratio of 0.95 or more are not obtained. Also, the fourth intermediate layer in which the material is differentiated from the third intermediate layer by adding B, O, or the like has a small increase in coercive force but little effect because the squareness ratio hardly increases. The fourth intermediate layer preferably contains Co, Cr, Ru, Ti, or the like as a main component and has a composition ratio of a six-method dense structure.
[0015]
The first intermediate layer preferably contains, as a main component, at least one element selected from the group consisting of Pd, Pt, Au, Ag, Rh, Ru, and Ti. According to the study performed by the inventors of the present application, it was found that the orientation of the first intermediate layer greatly affected the orientation of the recording layer. That is, if the (111) plane of the face-centered cubic structure or the (0001) plane of the hexagonal close-packed structure is oriented so as to be parallel to the substrate in the first intermediate layer, the (0001) orientation of the recording layer may be obtained. all right.
[0016]
When the first intermediate layer is an amorphous layer or an intermediate layer having a body-centered cubic structure, the recording layer is not vertically oriented, the coercive force is 100 kA / m or less, and the squareness ratio is 0.3 or less, which is not preferable. As a material of the first intermediate layer, it is preferable to use Pd, Au, Ag, Rh, Pt, Ru, Ti, or the like as a main component, but other face-centered cubic structures, hexagonal close-packed structures, or L10-type structures can be used. A material having such an ordered phase may be used. In this case, if the film thickness is 0.5 nm or more, a vertical orientation of the recording layer can be obtained.
[0017]
The second intermediate layer is preferably an oxygen-containing layer. This oxygen-containing layer has a small surface energy, and when a metal layer having a relatively large surface energy is formed on this surface, the metal layer does not cover the surface of the oxygen-containing layer in an area where the metal layer is thin, and is formed in an island shape. An isolated structure can be formed. Further, this structure can be controlled by the material, thickness, and formation temperature of the metal film. This oxygen-containing layer is made of MgO, SiO 2 , Al 2 O 3 , TiO, NiO or the like.
[0018]
The third intermediate layer preferably contains at least one element selected from the group consisting of Pd, Pt, Au, Ag, Rh, Ru, and Ti as a main component. Since the orientation of the third intermediate layer is determined by the first intermediate layer, it is preferable to use a material that maintains the orientation. In particular, when the same material as that of the first intermediate layer is used, the coercive force becomes the highest. However, a high coercive force can be obtained by using another material having a face-centered cubic structure or a hexagonal close-packed structure. The third intermediate layer becomes an island shape by being formed on the oxygen-containing layer, and its shape is determined by the melting point, the film thickness, and the substrate temperature of the material.
[0019]
The effect of the intermediate layer up to the above is increased by using Co as a main component as a perpendicular recording layer and containing oxygen. Since the oxide and the metal do not form a solid solution, when the oxide or the oxide is added to the recording layer to form the oxide, the oxide easily precipitates at the crystal grain boundary. In particular, since the intermediate layer has a structure in which a grain boundary is easily formed in shape, it is possible to form a recording layer in which the interaction between grains is sufficiently reduced. In this case, the substrate temperature for forming the recording layer needs to be 150 ° C. or lower. When the substrate temperature is high, oxides and oxygen are also present in the crystal grains, and the perpendicular magnetic anisotropy is greatly deteriorated, which is not preferable. It is more preferable to set the substrate temperature to 100 ° C. or lower, more preferably 70 ° C. or lower, because CoCrPt and oxides are completely separated.
[0020]
Further, a perpendicular magnetic recording medium of the present invention, a drive unit for driving the magnetic recording medium in a recording direction, a magnetic head including a recording unit and a reproducing unit, and the magnetic head relatively to the magnetic recording medium In a magnetic storage device including a moving unit and a recording / reproducing signal processing unit for performing waveform processing on an input signal and an output signal with respect to the magnetic head, a reproducing unit of the magnetic head includes a magnetoresistive element, Is a single pole type, a magnetic storage device having a recording density of 15 gigabits per square centimeter or more can be achieved.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
Hereinafter, a method for manufacturing the magnetic recording medium of this embodiment will be described. FIG. 1 is a sectional view schematically showing the configuration of a magnetic recording medium according to one embodiment of the present invention.
[0022]
After forming the Fe-8 at% Ta-12 at% C soft magnetic layers 11 and 11 'on a glass substrate 10 having an outer diameter of 65 mmφ by 400 nm, the substrate temperature is once increased to 440 ° C. and cooled to 280 ° C. The intermediate layers 12, 12 'were formed to a thickness of 1.5 nm. Next, the MgO second intermediate layers 13 and 13 'were formed to 1 nm, the Pd third intermediate layers 14 and 14' were formed to 1.5 nm, and the Ru fourth intermediate layers 15 and 15 'were formed to 3 nm. Further, after cooling the substrate temperature to 150 ° C. or lower, a magnetron cathode rotating in front of the substrate at a speed of 100 revolutions per minute in a circumferential direction is used to form a Co-13 at% Cr-20 at% Pt alloy target. SiO 2 The target was discharged simultaneously, and SiO2 was introduced into the CoCrPt alloy. 2 The recording layers 16 and 16 ′ were formed to a thickness of 20 nm by sputtering so that the content of the recording layers was 15 mol%. Finally, 5 nm of C was formed as the protective layers 17 and 17 '.
[0023]
In this embodiment, MgO and SiO 2 Was formed by the RF sputtering method, and in other cases, the film was formed by the DC magnetron sputtering method. Argon was used as a sputtering gas, and the pressure was set to 0.5 Pa when DC sputtering was performed, and to 2.0 Pa when performing MgO and RF sputtering at the time of forming the recording layer. Here, the numbers attached before the elements indicate the concentration of each element.
[0024]
Further, as Comparative Example 1, a medium in which a Pd-10 at% B intermediate layer having a thickness of 3 nm was formed using a mixed gas obtained by adding 3% oxygen to argon instead of the intermediate layers 15 and 15 '. The manufacturing conditions were the same except for the fourth intermediate layer. The medium of Example 1 used the Ru fourth intermediate layer, while the medium of Comparative Example 1 used the PdB fourth intermediate layer. It is a difference.
[0025]
Table 1 shows the magnetostatic characteristics of Example 1 and Comparative Example 1. A Kerr effect magnetometer was used to measure the magnetostatic characteristics, and a Kerr rotation angle was detected while applying a magnetic field perpendicular to the film surface of the sample, and a Kerr loop was measured. The sweep of the magnetic field was performed at a constant speed from plus 1750 kA / m to minus 1750 kA / m and from minus 1750 kA / m to plus 1750 kA / m in 64 seconds. As shown in Table 1, the medium of this example had higher coercive force and higher squareness than the medium of the comparative example.
[0026]
[Table 1]
Table 2 shows the evaluation results of the R / W characteristics of the spin stands of Example 1 and Comparative Example 1. The head used in this evaluation is a composite type head including a reproducing element utilizing a giant magnetoresistance effect having a shield gap length of 62 nm and a track width of 120 nm, and a single pole type writing element having a track width of 150 nm. Under the conditions of a peripheral speed of 10 m / s, a skew angle of 0 degree, and a magnetic spacing of about 15 nm, the reproduction output, medium noise, and thermal demagnetization characteristics were measured.
[0027]
The output resolution was the ratio of the reproduction output at a linear recording density of 23620 fr / mm to the reproduction output at a linear recording density of 1970 fr / mm, and the medium noise was noise at a linear recording density of 23620 fr / mm. The thermal demagnetization characteristic was defined as the amount of change in the reproduction output after a lapse of 1000 seconds from the recording of the signal of 3940 fr / mm. These values were set to 1 in the present example, and the values in Comparative Example 1 were indicated by relative values.
[0028]
[Table 2]
As shown in Table 2, this embodiment has higher output resolution characteristics, and is considered to be an effect of improving the squareness ratio according to the present invention. Since the medium noise is slightly lower in this embodiment, it is considered that grain boundary segregation is likely to be promoted. In addition, the amount of change in the reproduction output was smaller in the medium of the present example, and it was found that the medium of the present invention was also excellent in heat-resistant demagnetization characteristics.
[0029]
Here, the effect of the fourth intermediate layer was examined. FIG. 2 shows magnetostatic characteristics when a medium having the same structure as that of the first embodiment is manufactured and the thickness of the fourth intermediate layer is changed. Since a high squareness ratio is obtained by forming the fourth intermediate layer, it is considered that the Ru fourth intermediate layer has an effect of enhancing the vertical alignment. Since the coercive force exceeds 300 kA / m when the Ru film thickness is 0.5 nm, it was found that the fourth intermediate layer also has an effect of increasing the coercive force.
[0030]
Table 3 shows the magnetostatic characteristics when the material of the fourth intermediate layer is changed. A material having a large coercive force and a squareness ratio was obtained from a material having a hexagonal close-packed structure, and no material having another structure was able to achieve both a high coercive force and a squareness ratio. A material having a face-centered cubic structure has a high coercive force to some extent, but has a squareness of 0.9 or less. This is because the face-centered cubic structure and the hexagonal close-packed structure have the same atomic arrangement of the two-dimensional lattice, but the recording layer is a hexagonal close-packed structure. It is considered that since the crystal grains with disordered orientation are generated, the squareness ratio does not increase.
[0031]
[Table 3]
Further, the effect of the first intermediate layer was examined. Table 4 shows the magnetostatic characteristics when a medium having the same structure as that of the first embodiment was manufactured and the material of the first intermediate layer was changed. The large coercive force and squareness ratio were obtained when a material having a face-centered cubic structure or a hexagonal close-packed structure was used, and when a material having a body-centered cubic structure or an amorphous material was used, the coercive force and squareness were obtained. Only low values were obtained for both ratios.
[0032]
[Table 4]
Table 5 shows the results of examining the diffraction intensity of the (0001) plane of the recording layer with an X-ray diffractometer for the medium in which the material of the first intermediate layer was changed. In this case, the diffraction intensity was 1 in the case of the Pd intermediate layer, and the values of the other intermediate layers were indicated by relative values.
[0033]
[Table 5]
In the medium in which only a low coercive force was obtained, the (0001) plane was hardly oriented, and no diffraction peak could be observed in an amorphous material. The materials from which a large coercive force was obtained had a face-centered cubic structure and a hexagonal close-packed structure.
[0034]
Next, the magnetostatic characteristics when the thickness of the Pd first intermediate layer is changed are shown in FIG. If Pd is formed even at 0.5 nm, a high coercive force and a high squareness ratio are obtained, and the squareness ratio maintains a high value at any film thickness. Further, for a medium having a Pd film thickness of 5 nm, a medium was formed up to the first intermediate layer by the same manufacturing method as in Example 1, and the orientation of Pd was examined by an X-ray diffractometer. At this time, Pd had a (111) orientation, and no other diffraction peaks were observed. From this, it was found that the vertical orientation of the recording layer was obtained if the first intermediate layer maintained the (111) orientation.
[0035]
Next, the effect of the second intermediate layer was examined. Table 6 shows magnetostatic characteristics when a medium having the same structure as that of the first embodiment was manufactured and the material of the second intermediate layer was changed. Even when the second intermediate layer is made of another oxide, the same magnetostatic characteristics as those of Example 1 are obtained, indicating that the second intermediate layer is not limited to MgO but may be an oxygen-containing layer. Was.
[0036]
[Table 6]
Next, the effect of the third intermediate layer was examined. Table 7 shows the magnetostatic characteristics when a medium having the same structure as that of the first embodiment was manufactured and the material of the third intermediate layer was changed. The large coercive force and squareness ratio were obtained when using a material having a face-centered cubic structure or a hexagonal close-packed structure, and the coercive force and squareness ratio were low when using a body-centered cubic structure or an amorphous material. Only values were obtained. Since the (111) plane of the face-centered cubic structure or the (0001) plane of the hexagonal dense structure, which is the closest dense surface in the first intermediate layer, is oriented, the third intermediate layer is also made of a material having the same atomic arrangement. It was found that it was necessary to make a proper orientation.
[0037]
[Table 7]
Next, FIG. 4 shows the magnetostatic characteristics when the thickness of the third intermediate layer is changed. A large coercive force was obtained at 0.5 nm or more and 2.5 nm or less, and became maximum at a Pd film thickness of 1.5 nm. The cross-sectional structures of the samples having a Pd film thickness of 1.5 nm and 3 nm of these media were examined.
[0038]
FIG. 5 schematically shows a transmission electron microscope image obtained by observing the cross-sectional structure of the medium of this embodiment at a high magnification of about 1.25 million times. In the figure, 50 is a Pd first intermediate layer, 51 is a MgO second intermediate layer, 52 is a Pd third intermediate layer, 53 is a Ru fourth intermediate layer, and 54 is a recording layer. The MgO second intermediate layer 51 containing oxygen is clearly observed with bright contrast. The Pd third intermediate layer 52 serving as the island-shaped metal layer cannot be clearly recognized because the contrast difference between the Pd third intermediate layer 52 and the Ru fourth intermediate layer 53 is small. The recording layer 54 is made of SiO 2 Thereby, the grain boundaries can be clearly recognized.
[0039]
In the case of the Pd third intermediate layer thickness of 1.5 nm shown in FIG. 5A, the average thickness from the surface of the MgO second intermediate layer 51 to the grain boundary of the recording layer 54 was 2.9 nm. In this case, the total thickness of the third intermediate layer 52 and the fourth intermediate layer 53 is 4.5 nm, and the thickness of the intermediate layers 52 and 53 is reduced in the portion where the grain boundary of the recording layer 54 is formed. You can see that there is. This indicates that the intermediate layer is provided with irregularities, and it has been found that grain boundaries are formed in the concave portions and crystal grains are formed in the convex portions.
[0040]
On the other hand, when the thickness of the Pd third intermediate layer shown in FIG. 5B is 3 nm, the average thickness from the surface of the MgO second intermediate layer 51 to the grain boundary of the recording layer 54 is 5.4 nm. . This indicates that Pd is a substantially continuous film, and the uneven shape is hardly formed. This also affects the surface of the recording layer, and the Pd third intermediate layer 52 having a thickness of 1.5 nm shown in FIG. It is considered that the unevenness of 52 is affecting.
[0041]
Next, FIG. 6 shows the result of examining the average film thickness from the MgO intermediate layer to the grain boundary of the recording layer for the medium shown in FIG. It can be seen that in the region where the Pd film thickness is small, the average film thickness does not increase so much, and increases sharply when the Pd film thickness exceeds about 1.5 nm. As compared with the results in FIG. 4, the average film thickness at which a high coercive force was obtained was 0.5 nm or more and 4.5 nm or less.
[0042]
Next, the composition of the perpendicular recording layer was examined. FIG. 7 shows a medium having the same structure as in the first embodiment, 2 This shows the magnetostatic characteristics when the addition concentration is changed. High coercive force of 300 kA / m or more can be obtained by SiO 2 And the squareness ratio is SiO 2 or more. 2 If the additive concentration of is 20 mol% or more, it deteriorates. SiO 2 It is considered that the coercive force decreases in the low concentration region because the material that segregates at the grain boundaries is insufficient even in the intermediate layer in which the grain boundaries are easily formed in shape. Conversely, SiO 2 It is considered that the reason why the coercive force and the squareness ratio decrease when the concentration is high is that the crystal grain size becomes too small due to too much material that segregates at the grain boundaries.
(Example 2)
FIG. 8 is a sectional view schematically showing a configuration of a magnetic recording medium according to a second embodiment of the present invention. Hereinafter, a method for manufacturing the magnetic recording medium of this embodiment will be described.
[0043]
The perpendicular magnetic recording medium of this embodiment is manufactured with the same film configuration and the same process conditions as those of the first embodiment up to the fourth intermediate layers 85 and 85 ', and the recording layers 86 and 86' are formed by adding 0.5% of argon gas to argon gas. Was used as a sputtering gas, and Co-13 at% Cr-14 at% Pt was used as a target to form a film having a thickness of 20 nm. Finally, 5 nm of C was formed as the protective layers 87 and 87 '.
[0044]
Further, as Comparative Example 2, a medium in which a Pd-10 at% B intermediate layer was formed in the fourth intermediate layers 85 and 85 'in a thickness of 3 nm using a mixed gas in which 3% oxygen was added to argon instead of Ru was produced. The manufacturing conditions were the same except for the fourth intermediate layer. The medium of Example 2 used the Ru fourth intermediate layer, whereas the medium of Comparative Example 2 used the PdB fourth intermediate layer. It is a difference.
[0045]
Table 8 shows the magnetostatic characteristics of this example medium and Comparative Example 2. The measurement conditions were the same as in Example 1 above. Both the coercive force and the squareness ratio were higher in Example 2, and it was found that the intermediate layer of the present invention was applicable not only when an oxide was added to the recording layer but also when oxygen was added during the formation of the recording layer.
[0046]
[Table 8]
Table 9 shows the R / W characteristics of the medium of Example 2 and Comparative Example 2. The measurement conditions were the same as those in Example 1 described above, and the value in Example 2 was set to 1 and the value in Comparative Example 2 was shown as a relative value. This embodiment is considered to have an effect that the output resolution characteristic is higher and the squareness ratio is improved. It is considered that the medium noise is lower in this embodiment, and that the grain boundary segregation is promoted. Also, the amount of change in the reproduction output was smaller in the medium of the present example, and it was found that the medium of the present invention was also excellent in the heat-resistant demagnetization characteristics. It is considered that Co or Cr is converted into an oxide by the oxygen-introduced sputtering, segregated at the crystal grain boundaries, and the intergranular interaction is reduced.
[0047]
[Table 9]
Next, FIG. 9 shows the magnetostatic characteristics of the medium having the same structure as that of the second embodiment when the temperature for forming the first intermediate layer is changed. At this time, the substrate temperature during the formation of the intermediate layer was changed by changing the cooling time after heating the soft magnetic layer, and cooling was performed before the formation of the recording layer so that the substrate temperature during the formation of the recording layer was the same.
[0048]
The coercive force becomes 300 kA / m or more when the substrate temperature is set to 200 ° C. or more, but the squareness ratio rapidly deteriorates when the substrate temperature is set to 350 ° C. or more. This is thought to be due to the fact that the uneven shape of the intermediate layer formed on MgO changes depending on the temperature at which the intermediate layer is formed, which affects the orientation. It is considered that the above reaction occurs to deteriorate the orientation.
[0049]
FIG. 10 shows the magnetostatic characteristics when the substrate temperature during the formation of the recording layer is changed. If the substrate temperature exceeds 150 ° C. when forming the recording layer, the coercive force becomes 300 kA / m or less, and the coercive force increases as the substrate temperature decreases. When the temperature at the time of forming the recording layer is high, it is considered that the magnetic anisotropy is deteriorated due to the inclusion of the oxide in the crystal grains or the oxidization of Co more than necessary.
(Example 3)
Next, in a medium having the same film configuration as that of the above-mentioned Example 2, Example 3 was manufactured using an artificial lattice film as a recording layer. The formation of the artificial lattice film was performed by simultaneously discharging a Co-10 at% B target and a Pd target using a magnetron cathode rotating at a speed of 100 rotations per minute. In this case, the film thickness was set to 0.3 nm for CoB and 1.2 nm for Pd, and 15 layers each were laminated. As a sputtering gas, a mixed gas obtained by adding 1% of oxygen to argon was used, and the gas pressure was 7 Pa.
[0050]
Table 10 shows the magnetostatic properties of Example 3 and Comparative Example 2. The coercive force of Example 3 was as high as 530 kA / m, and the squareness ratio was 1.0. Table 11 shows the R / W characteristics of Example 3 and Comparative Example 2. The measurement conditions were the same as those in Example 1 described above, and the values in Example 3 were set to 1 and the values in Comparative Example 2 were indicated by relative values. The third embodiment has a higher output resolution characteristic, and the medium noise is lower in the third embodiment. Further, in this example, there was almost no change in the reproduction output, and it was found that the medium of the present invention was also excellent in the heat-resistant demagnetization characteristics. From this, it was confirmed that the intermediate layer of the present invention was effective even when the recording layer was an artificial lattice film.
[0051]
[Table 10]
[Table 11]
(Example 4)
The magnetic recording medium of the above embodiment can sufficiently exhibit its performance by being incorporated in a magnetic storage device as shown in an example in FIG. FIG. 11A is a top view of the magnetic storage device, and FIG. 11B is a cross-sectional view taken along the line AA ′.
[0052]
The magnetic recording medium 110 is held by a holder connected to the magnetic recording medium driving unit 111, and a magnetic head 112 is arranged to face each surface of the magnetic recording medium 110. The magnetic head 112 is stably and low-flying at a magnetic flying height of 0.015 μm or less, and is driven by the magnetic head drive unit 113 to a desired track with a head positioning accuracy of 0.03 μm or less.
[0053]
The signal reproduced by the magnetic head 112 is subjected to waveform processing by a recording / reproducing signal processing system 114. The recording / reproducing signal processing system 114 includes an amplifier, an analog equalizer, an AD converter, a digital equalizer, a maximum likelihood decoder, and the like. The reproduced waveform of the head using the magnetoresistive effect is different from the recorded signal because the positive and negative magnitudes are asymmetrical due to the characteristics of the head and the frequency characteristics of the recording / reproducing system affect it. May be misread. The analog equalizer has a function of adjusting a reproduced waveform and restoring the waveform. The restored waveform is converted into a digital signal through an AD converter, and the waveform is further adjusted by a digital equalizer. Finally, the restored signal is demodulated by the maximum likelihood decoder into the most likely data. With the reproduction signal processing system having the above configuration, recording and reproduction of signals are performed at an extremely low error rate. Note that existing equalizers and maximum likelihood decoders may be used.
[0054]
With the above-described device configuration, the recording density per square centimeter can correspond to 15 gigabits or more, and a high-density magnetic storage device having a storage capacity three times or more that of a conventional magnetic storage device is realized. I was able to. Further, even when the maximum likelihood decoder is removed from the recording / reproducing signal processing system and replaced with a conventional waveform discriminating circuit, a magnetic storage device having a storage capacity twice or more as compared with the conventional one can be realized.
[0055]
【The invention's effect】
In a magnetic recording medium having a structure having a soft magnetic layer, an intermediate layer, a perpendicular recording layer, and a protective layer on a substrate, the first intermediate layer is formed of Pd, Pt, Au, Ag, Rh, Ru, and Ti from the side near the substrate. A metal layer mainly containing at least one element selected from the group consisting of: a second intermediate layer is an oxygen-containing layer; and a third intermediate layer is Pd, Pt, Au, Ag, Rh, Ru. , Ti is a metal layer mainly containing at least one element selected from the group consisting of Ti, and the fourth intermediate layer is mainly composed of at least one element selected from Co, Cr, Ru, and Ti. The perpendicular recording layer has a high coercive force and a high squareness ratio, has low noise, and has little influence of thermal fluctuation, because the perpendicular recording layer contains Co as a main component and contains oxygen. Can be realized.
[0056]
Further, by combining this magnetic recording medium with a magnetic head having a read-only element utilizing the magnetoresistance effect, a magnetic storage device having a recording density of 15 gigabits per square centimeter or more can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a perpendicular magnetic recording medium according to an embodiment of the present invention.
FIG. 2 is a diagram showing the dependence of magnetostatic characteristics on a fourth intermediate layer thickness.
FIG. 3 is a diagram showing the dependence of magnetostatic characteristics on the thickness of a first intermediate layer.
FIG. 4 is a diagram showing the dependence of magnetostatic characteristics on the thickness of a third intermediate layer.
FIG. 5 is a schematic cross-sectional view of a cross section of a perpendicular magnetic recording medium according to one embodiment of the present invention when observed with a transmission electron microscope.
FIG. 6 is a diagram showing the dependence of the average film thickness from the MgO intermediate layer to the grain boundary of the recording layer on the Pd film thickness.
FIG. 7 is a diagram showing the dependency of magnetostatic characteristics on the concentration of SiO 2 in a recording layer.
FIG. 8 is a schematic sectional view of a magnetic recording medium according to an embodiment of the present invention.
FIG. 9 is a view showing the substrate temperature dependence of magnetostatic characteristics when an intermediate layer is formed.
FIG. 10 is a diagram showing the substrate temperature dependence of magnetostatic characteristics when a recording layer is formed.
FIG. 11 is a schematic view of a magnetic storage device according to an embodiment of the present invention.
[Explanation of symbols]
Reference numeral 10: substrate, 11, 11 ': FeTaC soft magnetic layer, 12, 12': Pd first intermediate layer, 13, 13 ': MgO second intermediate layer, 14, 14': Pd third intermediate layer, 15, 15 '... Ru fourth intermediate layer, 16,16' ... CoCrPtSiO2 recording layer, 17,17 '... C protective layer, 50 ... Pd first intermediate layer, 51 ... MgO second intermediate layer, 52 ... Pd third intermediate layer, 53: Ru fourth intermediate layer, 54: recording layer, 80: substrate, 81, 81 ': FeTaC soft magnetic layer, 82, 82': Pd first intermediate layer, 83, 83 ': MgO second intermediate layer, 84 , 84 '... Pd third intermediate layer, 85, 85'... Ru fourth intermediate layer, 86, 86 '... CoCrPtO recording layer, 87, 87'... C protective layer, 110.. Driving unit, 112: magnetic head, 113: magnetic head driving unit, 114: recording / reproducing signal processing System.