JP3999978B2 - Magneto-optical recording medium - Google Patents

Description

【００３６】
以上の如き膜構成の光磁気ディスク１に、最短マーク長が0.38μｍのランダムデータを光変調記録し、線速7.5 ｍ／ｓで再生して評価した。再生時には記録マークの記録方向と同方向の再生磁界を300 Ｏｅで印加した。再生レーザ光は光磁気ディスク１の基板１２側から照射された。図２は、図１の光磁気ディスクの膜構成及び再生時の磁化状態を示す図であり、再生層，中間層及び記録層のみを示し、その他の膜層は省略している。図２に示すように、光磁気ディスク１が回転し、再生用レーザ光が磁性層に照射されたとき温度分布が生じる。低温領域では、中間層１５と記録層１６との間に作用する交換結合力よりも再生磁界が大きい場合に、中間層１５の磁化方向が再生磁界と同方向に揃う。中間層１５と交換結合した再生層１４の磁化方向は記録マークと無関係に再生磁界と逆方向に揃い、これによりフロントマスクが形成される。高温領域では、再生層１４と中間層１５との間に作用する交換結合力が切断され、再生層の磁化方向が再生磁界と同方向に揃うことによりリアマスクが形成される。中間温度領域では、再生層１４、中間層１５及び記録層１６間に再生磁界よりも大きな交換結合力がはたらいており、記録層１６の磁化方向が再生層１４に転写される。
【００３７】
このように光磁気ディスク１の磁気光学的出力を検出した場合に、レーザスポット内において低温領域及び高温領域にはマスクが形成されているので光磁気信号を読出すことはなく、中間温度領域のみから光磁気信号を読出すことができる。
【００３８】
図３は、光磁気ディスク１のジッタの記録パワーマージンを示すグラフである。縦軸はランダムジッタを示し、横軸はレーザ光の記録パワーを示している。実用上はランダムジッタが12.5％以下であることが好ましい。グラフから、光磁気ディスク１のジッタの記録パワーマージンは±１１％を示していることが判る。これは実用上十分な値である。
【００３９】
このように、実施の形態１の光磁気ディスク１は、トラックピッチが0.9 μｍで最短記録マークが0.38μｍであるので、1.3 ＧＢの記録容量を有する高密度記録の光磁気ディスクの再生が、十分なジッタの記録パワーマージンを有して実現できたと言える。
【００４０】
上述した如き膜構成の光磁気ディスクで、高密度記録された情報のＭＳＲ再生が可能となる磁性膜の磁気特性を調べた。まず、300 Ｏｅの再生磁界の印加で再生できる各磁性層の飽和磁化の範囲を調べた。図４は、再生層の組成によるリアマスク形成の必要再生磁界の変化を示すグラフである。縦軸はリアマスクを形成するために必要な再生磁界Ｈrearを示し、横軸は再生層の飽和磁化Ｍｓ１を示している。グラフから、300 Ｏｅ以内の磁界で再生するためには再生層１４の飽和磁化Ｍｓ１は８emu/cc以上の値が必要であることが判る。
【００４１】
再生層１４の飽和磁化が大きくなると、再生信号の品質劣化の程度が大きくなる。図５は、再生層の飽和磁化と再生信号品質との関係を示すグラフである。縦軸は、基準ＣＮＲとの差であるΔＣＮＲを示し、横軸は再生層の飽和磁化Ｍｓ１を示している。ΔＣＮＲは、最適記録パワーに対して略13％増しの消去パワーで10万回連続消去したときの信号品質の劣化の度合いを測定している。グラフから、ΔＣＮＲの許容範囲である１ｄＢ以内で、再生層１４の飽和磁化Ｍｓ１は100 emu/cc以下であることが判る。
【００４２】
図６は、中間層の組成によるフロントマスク形成の必要再生磁界の変化を示すグラフである。縦軸はフロントマスクを形成するために必要な再生磁界Ｈfront を示し、横軸は中間層の飽和磁化Ｍｓ２を示している。グラフから、300 Ｏｅ以内の磁界で再生するためには中間層１５の飽和磁化Ｍｓ２は140 emu/cc以上の値が必要であることが判る。図７は、中間層の飽和磁化と再生信号品質との関係を示すグラフである。縦軸は、基準ＣＮＲとの差であるΔＣＮＲを示し、横軸は中間層の飽和磁化Ｍｓ２を示している。ΔＣＮＲは、最適記録パワーに対して略13％増しの消去パワーで10万回連続消去したときの信号品質の劣化の度合いを測定している。グラフから、ΔＣＮＲの許容範囲である１ｄＢ以内で、中間層１５の飽和磁化Ｍｓ２は250 emu/cc以下であることが判る。
【００４３】
図８は、記録層の組成によるフロントマスク形成の必要再生磁界の変化を示すグラフである。縦軸はフロントマスクを形成するために必要な再生磁界Ｈfront を示し、横軸は記録層の飽和磁化Ｍｓ３を示している。グラフから、300 Ｏｅ以内の磁界で再生するためには記録層１６の飽和磁化Ｍｓ３は50emu/cc以上の値が必要であることが判る。図９は、記録層の飽和磁化と再生信号品質との関係を示すグラフである。縦軸は、基準ＣＮＲとの差であるΔＣＮＲを示し、横軸は記録層の飽和磁化Ｍｓ３を示している。ΔＣＮＲは、最適記録パワーに対して略13％増しの消去パワーで10万回連続消去したときの信号品質の劣化の度合いを測定している。グラフから、ΔＣＮＲの許容範囲である１ｄＢ以内で、記録層１６の飽和磁化Ｍｓ３は150 emu/cc以下であることが判る。
【００４４】
以上のことから、1.3 ＧＢ程度の記録容量を有する光磁気ディスクを、300 Ｏｅ以下の再生磁界の印加で再生できる各磁性層の飽和磁化の範囲は、再生層１４は８emu/cc〜100 emu/ccであり、中間層１５は140 emu/cc〜250 emu/ccであり、記録層１６は50emu/cc〜150 emu/ccであると言える。上述した実施の形態１の光磁気ディスク１はこの条件を満たしている。
【００４５】
次に、現行の光磁気ドライブを用いて再生できる各磁性層のキュリー温度の範囲を調べた。図１０は、記録層のキュリー温度に対して変化する、記録パワーの室温における感度を示すグラフである。3.5 インチの最外周条件においての値である。縦軸はレーザ光の記録パワーを示し、横軸は記録層１６のキュリー温度Ｔｃ３を示している。記録パワー感度は、信号が出始めるパワーＰwth と十分に信号が得られるパワーＰｗとの両方を示している。図１１は光磁気ディスクの環境温度と記録パワーとの関係を示すグラフである。縦軸は記録パワーを示し、横軸は環境温度を示している。線速12.6ｍ／ｓでの測定結果である。図１１から、環境温度が低いほど、より高い記録パワーが必要であることが判る。
【００４６】
図１０に示すように、光磁気ドライブが有するレーザダイオードのパワー限界が略13ｍＷである場合、記録パワーＰwth に関してはキュリー温度Ｔｃ３は450 ℃まで許容されると言えるが、実際には十分に信号が得られる記録パワーが用いられること、また図１１に示すように、環境温度が０℃まで動作を保証するためにはより高い記録パワーが必要であることから、記録層１６のキュリー温度Ｔｃ３は350 ℃が上限であると言える。
【００４７】
図１２は、中間層のキュリー温度に対して変化する、再生パワーの感度を示すグラフである。縦軸はレーザ光の再生パワーを示し、横軸は中間層１５のキュリー温度Ｔｃ２を示している。再生パワー感度は、信号が出始めるパワーＰrth について環境温度が０℃と２５℃との場合を示し、０℃で十分に信号が得られるパワーＰｒについても示している。グラフから判るように、２５℃よりも０℃の方がより高い再生パワーが必要になる。実際に十分に信号が得られる再生パワーＰｒはさらに高い値を示しており、高周波重畳の限界が6.4 ｍＷである場合に、中間層１５のキュリー温度Ｔｃ２は220 ℃が上限であると言える。
【００４８】
図１３は、中間層の磁化容易軸特性と再生磁界との関係を示すグラフである。縦軸は再生磁界を示し、横軸は中間層１５が面内磁化から垂直磁化に変わる温度を示している。グラフから判るように、中間層が垂直磁化に変わる温度が高温になるほど再生磁界の値は低くなる。300 Ｏｅ以下の再生磁界で再生するためには、垂直磁化に変わる温度は130 ℃以上が必要であることが判る。また、図１４は、中間層のキュリー温度と磁化容易軸特性との関係を示すグラフである。縦軸は中間層１５が面内磁化から垂直磁化に変わる温度を示し、横軸は中間層１５のキュリー温度Ｔｃ２を示している。グラフから、垂直磁化に変わる温度が130 ℃以上である中間層１５のキュリー温度Ｔｃ２は160 ℃以上であることが判る。
【００４９】
中間層１５のキュリー温度Ｔｃ２が160 ℃以上である場合の再生パワーＰrth は、図１２に示すように、略4.1 ｍＷ以上である。再生信号が見えてから消え始めるまでに±２０％程度の十分な再生パワーマージンを確保するためには、再生信号が4.1 ｍＷから見え始めた場合は、消え始める再生パワーＰeth は6.2 ｍＷとなる。図１５は、記録層のキュリー温度とレーザ光のパワーとの関係を示すグラフである。縦軸はレーザ光のパワーを示し、横軸は記録層１６のキュリー温度Ｔｃ３を示している。グラフから、再生パワーＰeth が6.2 ｍＷ以上では、記録層１６のキュリー温度Ｔｃ３は240 ℃以上が必要であることが判る。
【００５０】
再生層１４は記録層１６に形成された記録マークを再生する必要があるので、再生層１４のキュリー温度Ｔｃ１の範囲は記録層１６と同じであり、240 ℃〜350 ℃である。
【００５１】
以上のことから、1.3 ＧＢ程度の記録容量を有する光磁気ディスクを、現行の光磁気ドライブを使用して再生できる各磁性層のキュリー温度の範囲は、再生層１４は240 ℃〜350 ℃であり、中間層１５は160 ℃〜220 ℃であり、記録層１６は240 ℃〜350 ℃であると言える。上述した実施の形態１の光磁気ディスク１は、この条件を満たしている。
【００５２】
このような飽和磁化及びキュリー温度の範囲から外れた磁性層を有する比較例の光磁気ディスクについて、実施の形態１と同様に形成された記録マークを再生し、評価した。この光磁気ディスクは実施の形態１と同様の基板を備え、再生層１４及び記録層１６は補償組成、即ち自発磁化Ｍｓの値がほぼ零であり、中間層１５のキュリー温度Ｔｃ２は150 ℃である。図１６は、比較例の光磁気ディスクのジッタの記録パワーマージン及び必要再生磁界を示すグラフである。縦軸はランダムジッタを示し、横軸はレーザ光の記録パワーを示している。グラフ中、‘○’は再生磁界が300 Ｏｅの場合を、‘△’は350 Ｏｅの場合を、‘□’は400 Ｏｅの場合を示している。
【００５３】
比較例の光磁気ディスクは、繰り返し連続消去における耐久性は高く、10万回消去後でも信号品質の劣化はほとんど見られなかった。しかしながら、実施の形態１の光磁気ディスクと比較して（図３参照）ボトムジッタの値が高い。また、ランダムジッタが12.5％以下である記録パワーマージンは±8.3 ％であり、実施の形態１の光磁気ディスク１よりも狭いことが判った。さらに、再生磁界は300 Ｏｅでは再生できず、350 Ｏｅ以上が必要であった。
【００５４】
実施の形態２．
実施の形態１と同様の膜構成を有する光磁気ディスクを、トラックピッチが異なる基板を用いて形成し、２Ｔ＝0.4 μｍのマークを記録した。夫々の光磁気ディスクについて、必要再生磁界及びＣＮＲを調べた。図１７はその結果を示すグラフであり、縦軸はＣＮＲ及び必要再生磁界Ｈrth を示し、横軸はトラックピッチを示している。グラフから、トラックピッチが狭くなるほどＣＮＲが低下する傾向が見られる。特に、トラックピッチが0.9 μｍより狭い場合は1.1 μｍの場合と比較して1.5 ｄＢ以上、ＣＮＲが劣化していると言える。必要再生磁界はトラックピッチに対して大きな変化はなかった。
【００５５】
次に、実施の形態１と同様の膜構成を有する光磁気ディスクを、トラックピッチが異なるグルーブ基板を用いて形成し、夫々について同様に必要再生磁界及びＣＮＲを調べた。図１８はその結果を示すグラフであり、縦軸はＣＮＲ及び必要再生磁界Ｈrth を示し、横軸はトラックピッチを示している。グルーブ基板を用いた場合は、グラフから、トラックピッチが1.1 μｍから0.85μｍまでＣＮＲの低下は見られないが、0.9 μｍ以下で必要再生磁界が急激に大きくなっていることが判る。図１７及び図１８から、この膜構成の光磁気ディスクを用いて１ＧＢ以上の記録容量を実現するために、トラックピッチは0.9 μｍまで狭くできることが判る。また、ランド基板を用いることにより、狭いトラックピッチで、300 Ｏｅ以下の再生磁界でのＭＳＲ再生が可能であると言える。
【００５６】
さらに狭いトラックピッチでの再生を可能とするために、上述したグルーブ基板を用いて、フロントマスク及びリアマスク夫々について必要再生磁界を調べた。図１９はその結果を示すグラフであり、縦軸は必要再生磁界を示し、横軸はトラックピッチを示している。グラフから明らかなように、トラックピッチが0.9 μｍよりも狭いときに、フロントマスクの形成に必要な再生磁界が急激に大きくなっている。このことから、トラックピッチが狭くなると必要再生磁界が増大する原因は、フロントマスク形成のためであることが判る。そこで、フロントマスクを形成するための再生磁界を低減できる記録層１６の組成について調べた。図２０はその結果を示すグラフであり、縦軸はフロントマスクを形成するために必要な再生磁界を示し、横軸は記録層１６のＴｂ含有量を示している。グラフ中、‘○’はランド基板、‘×’はグルーブ基板についてのものである。グラフから、300 Ｏｅ以下の再生磁界で再生可能な記録層１６の組成範囲は、ランド基板と比較してグルーブ基板の方が狭いことが判る。
【００５７】
以上、図１８〜図２０に示すことから、0.9 μｍ程度の狭いトラックピッチで、300 Ｏｅ以下の再生磁界を用いてのＭＳＲ再生は、グルーブ基板よりもランド基板の方が適していると言える。また、グルーブ基板であっても記録層１６のＴｂ含有量を調整することにより上述のＭＳＲ再生は可能であるが、記録層１６の組成マージンはランド基板よりもグルーブ基板の方が狭いことが判った。また、これらのことから、ランド基板及びグルーブ基板のいずれにおいても、記録層１６の飽和磁化を調整することにより必要再生磁界の大きさを調整できることが判る。即ち、基板のトラックピッチに応じて記録層１６の組成を設定し、所望の大きさの再生磁界を印加してＭＳＲ再生できる。
【００５８】
実施の形態３．
上述した実施の形態１と同様の光磁気ディスクを、ＡｌＣｒからなる熱伝導層１８の膜厚のみを異ならせて形成し、記録パワー感度及び信号品質としてＳＮＲを測定した。その結果、熱伝導層１８の膜厚が８ｎｍのものは、20ｎｍのものよりもＳＮＲが２ｄＢ程度低く、そのためにジッタの極小値が十分に低い値を示していない。また、熱伝導層１８の膜厚が10ｎｍ以上のものは、実施の形態１と同程度の低いジッタを示した（図３参照）。さらに、熱伝導層１８の膜厚が30ｎｍのものは、８ｎｍのものよりも記録パワー感度が２ｍＷ程度悪く、そのために現行の光磁気ドライブを用いての再生が困難である。これらのことから、ＡｌＣｒの熱伝導層１８の膜厚は10ｎｍ〜25ｎｍが好ましいことが判る。
【００５９】
また、熱伝導層１８としてＡｌＴｉ膜を用いた場合でも、光磁気ディスクは実施の形態１と同様の再生特性を示した。そして、ＡｌＴｉ膜の膜厚のみを異ならせて光磁気ディスクを形成し、その膜厚に対する記録パワー感度及びＳＮＲを測定した。その結果、熱伝導層１８の膜厚が３ｎｍのものは、15ｎｍのものよりもＳＮＲが２ｄＢ程度低く、そのためにジッタの極小値が十分に低い値を示していない。また、熱伝導層１８の膜厚が25ｎｍのものは、３ｎｍのものよりも記録パワー感度が２ｍＷ程度悪く、そのために現行の光磁気ドライブを用いての再生が困難である。これらのことから、ＡｌＴｉの熱伝導層１８の膜厚は５ｎｍ〜20ｎｍが好ましいことが判る。従って、本発明に係る光磁気ディスクの熱伝導層１８の膜厚の最適な範囲は５ｎｍ〜25ｎｍであると言える。
【００６０】
実施の形態４．
上述した実施の形態１と同様の光磁気ディスク１を、ＳｉＮからなる下地誘電体層１３の膜厚のみを異ならせて形成し、反射率、記録パワー感度及びＳＮＲを測定した。その結果、下地誘電体層１３の膜厚が75ｎｍ近傍のものが反射率の極小値を示した。下地誘電体層１３の膜厚が60ｎｍのものは、90ｎｍのものよりもＳＮＲが1.6 ｄＢ程度低く、また下地誘電体層１３の膜厚が98ｎｍのものは、60ｎｍのものよりも記録パワー感度が1.5 ｍＷ程度悪化した。これらのことから、光磁気ディスク１の下地誘電体層１３の膜厚は65ｎｍ〜95ｎｍが好ましいことが判った。但し、この範囲は熱伝導層１８をＡｌＣｒ膜で形成した場合である。熱伝導層１８をＡｌＴｉで形成した場合は、下地誘電体層１３の膜厚が105 ｎｍで十分な記録パワーが得られ、115 ｎｍで許容範囲外であった。従って、本発明に係る光磁気ディスクの下地誘電体層１３の膜厚の最適な範囲は65ｎｍ〜110 ｎｍであると言える。
【００６１】
次に、実施の形態１と同様の光磁気ディスクを、ＳｉＮからなる上地誘電体層１７の膜厚のみを異ならせて形成し、記録パワー感度及び環境温度耐久性を測定した。その結果、上地誘電体層１７の膜厚が15ｎｍのものは、温度80℃，湿度85％の環境下で200 時間後に腐食のような欠陥が生じた。また、上地誘電体層１７の膜厚が65ｎｍのものは、20ｎｍのものよりも記録パワー感度が２ｍＷ程度悪化した。これらのことから、本発明に係る光磁気ディスクの上地誘電体層１７の膜厚は20ｎｍ〜60ｎｍが好ましいと言える。
【００６２】
実施の形態５．
上述した実施の形態１と同様の光磁気ディスクを、基板１２のみを異ならせて形成した。実施の形態５の基板は、グルーブの深さは93ｎｍ（λ／（4.4n）ｎｍ），ランド幅は0.75μｍのポリカーボネート製のランド基板である。その他の寸法及び構成は実施の形態１と同様であり、その説明を省略する。このような光磁気ディスクについてランダムジッタを評価した。図２１はその結果を示すグラフである。縦軸はランダムジッタを示し、横軸はレーザ光の記録パワーを示している。グラフから、ランダムジッタが12.5％以下である記録パワーマージンは、±11％であることが判る。従って、高密度記録された実施の形態５の光磁気ディスクのジッタの記録パワーマージンは±１１％を示していることが判る。これは実用上十分な値である。
【００６３】
実施の形態６．
図２２は実施の形態６の光磁気ディスクの膜構成を示す断面図である。光磁気ディスク２はポリカーボネート製の基板１２上に、ＡｌＣｒからなる熱伝導層１８、ＳｉＮからなる下地誘電体層１３、ＴｂＦｅＣｏからなる記録層１６、ＧｄＦｅＣｏＳｉからなる中間層１５、ＧｄＦｅＣｏからなる再生層１４及びＳｉＮからなる上地誘電体層１７を積層して構成されており、光磁気ディスク２の最外層、即ち基板１２と上地誘電体層１７との夫々の表面が第１及び第２の紫外線硬化膜１１，１９で被覆されている。光磁気ディスク２は膜の積層順序が異なることの他は図１に示す光磁気ディスク１と同様であり、各磁性膜の飽和磁化，キュリー温度などの磁気特性及び膜厚、並びに基板仕様については説明を省略する。
【００６４】
以上の如き膜構成の光磁気ディスク２に、最短マーク長が0.38μｍのランダムデータを光変調記録し、線速7.5 ｍ／ｓで再生して評価した。再生時には記録マークの記録方向と同方向の再生磁界を300 Ｏｅで印加した。また、再生レーザ光は基板１２から遠い側、即ち再生層１４に近い側から照射された。その結果、1.3 ＧＢの記録容量を有する高密度記録の光磁気ディスク２の再生が、実施の形態１と同様に、十分なジッタの記録パワーマージンを有して実現できることが判った。
【００６５】
なお、本発明の光磁気記録媒体の再生層、中間層及び記録層は、上述した実施の形態１〜実施の形態６の光磁気ディスクに用いた磁性膜には限らない。上述した範囲の磁気特性を有する磁性膜であれば、3.5 インチ径で片面1.3 ＧＢの高密度記録された媒体をＭＳＲ再生できる。
【００６６】
【発明の効果】
以上のように、本発明においては、所定範囲の飽和磁化を有する磁性膜を用いて光磁気記録媒体を形成してあるので、トラックピッチが0.9 μｍ、最短マーク長が0.38μｍ程度の高密度記録媒体を、再生磁界が300 Ｏｅ以下でＭＳＲ再生することが可能となる。また、所定範囲のキュリー温度を有する磁性膜を用いて光磁気記録媒体を形成してあるので、現行の光磁気ドライブを用いての再生が可能となり、現状媒体との互換性を保つことができる。さらに、このような光磁気記録媒体は、繰り返し記録／再生に対する耐久性に優れている。さらにまた、磁性膜をその飽和磁化が所定の値になるように成膜することにより、所望の磁気特性を有する光磁気記録媒体を再現性良く製造でき、高密度記録再生が確実となる等、本発明は優れた効果を奏する。
【図面の簡単な説明】
【図１】本発明の光磁気ディスクの膜構成を示す断面図である。
【図２】本発明の光磁気ディスクの膜構成と再生時の磁化状態を示す図である。
【図３】実施の形態１の光磁気ディスクのジッタの記録パワーマージンを示すグラフである。
【図４】再生層の飽和磁化とマスク形成の必要再生磁界との関係を示すグラフである。
【図５】再生層の飽和磁化と再生信号品質との関係を示すグラフである。
【図６】中間層の飽和磁化とマスク形成の必要再生磁界との関係を示すグラフである。
【図７】中間層の飽和磁化と再生信号品質との関係を示すグラフである。
【図８】記録層の飽和磁化とマスク形成の必要再生磁界との関係を示すグラフである。
【図９】記録層の飽和磁化と再生信号品質との関係を示すグラフである。
【図１０】記録層のキュリー温度と記録パワーとの関係を示すグラフである。
【図１１】光磁気ディスクの環境温度と記録パワーとの関係を示すグラフである。
【図１２】中間層のキュリー温度と再生パワーとの関係を示すグラフである。
【図１３】中間層の磁化容易軸特性と再生磁界との関係を示すグラフである。
【図１４】中間層のキュリー温度と磁化容易軸特性との関係を示すグラフである。
【図１５】記録層のキュリー温度とレーザ光のパワーとの関係を示すグラフである。
【図１６】比較例のジッタの記録パワーマージン及び必要再生磁界を示すグラフである。
【図１７】実施の形態２のランド記録ディスクのトラックピッチに対する再生特性及び必要再生磁界を示すグラフである。
【図１８】実施の形態２のグルーブ記録ディスクのトラックピッチに対する再生特性及び必要再生磁界を示すグラフである。
【図１９】実施の形態２のトラックピッチに対するマスク形成の必要再生磁界の関係を示すグラフである。
【図２０】実施の形態２の記録層とマスク形成の必要再生磁界の関係を示すグラフである。
【図２１】実施の形態５の光磁気ディスクのジッタの記録パワーマージンを示すグラフである。
【図２２】実施の形態６の光磁気ディスクの膜構成を示す断面図である。
【符号の説明】
１，２ 光磁気ディスク
１１，１９ 紫外線硬化膜
１２ 基板
１３ 下地誘電体層
１４ 再生層
１５ 中間層
１６ 記録層
１７ 上地誘電体層
１８ 熱伝導層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magneto-optical recording medium such as a magneto-optical disk, a magneto-optical tape, and a magneto-optical card, and more particularly to a magneto-optical recording medium capable of reproducing magnetically super resolution (Magnetically Induced Super Resolution).
[0002]
[Prior art]
The magneto-optical disk is positioned as a central existence of a memory for storing a large amount of data in preparation for the future multimedia age, and further increase in recording capacity is demanded. In order to increase the recording density of the magneto-optical disk, it is necessary to make the recording mark length shorter than the spot diameter of the laser beam and reduce the recording mark interval. It is relatively easy to form such a fine recording mark, but when reproducing a fine recording mark, reproduction is possible due to the restriction of the wavelength λ of the laser beam to be irradiated and the numerical aperture NA of the objective lens. There was a limit to the length of various recording marks.
[0003]
Therefore, various magnetic super-resolution (MSR) reproducing methods capable of reproducing a recording mark smaller than the laser beam diameter have been proposed. In these methods, a temperature distribution is generated in the circumferential direction of the magneto-optical disk by irradiating the reproducing laser light while rotating the magneto-optical disk in which a plurality of magnetic layers including a recording layer and a reproducing layer are laminated. A small recording mark is read using this temperature distribution. As a result, the same resolution as that obtained when reproducing with a light spot substantially smaller than the spot diameter of the reproduction laser beam can be obtained.
[0004]
However, these conventional methods have some problems as described below. First, the method of reading the recording mark from the low temperature region in the spot is excellent in the resolution in the circumferential direction, but the crosstalk affected by the adjacent track is large. In addition, the method of reading the recording mark from the high temperature area in the spot reduces the crosstalk, but it is necessary to use a large initialization magnet of 3.5 to 4 kOe to initialize the reproducing layer, and the apparatus is downsized. Can not. Furthermore, in the method in which the recording mark is read from the area where the magnetization direction of the reproducing layer changes from the in-plane direction to the vertical direction due to the temperature distribution, reproduction can be performed without using a large initialization magnet. However, high playback output cannot be obtained. Further, in order to narrow the transferred area in the spot and increase the resolution, a method of reading the recording mark from only the intermediate temperature region has been proposed. However, a reproducing magnetic field of several hundred Oe is applied and several kOe of several kOe is applied. An initialization magnet was required.
[0005]
Therefore, the applicant of the present application has proposed an MSR regeneration method that can solve these problems (Japanese Patent Laid-Open No. 7-244877). By this reproducing method, information is read from the intermediate temperature region by applying a reproducing magnetic field of several hundred Oe, that is, a double mask is formed, and high-resolution reproduction is realized without using an initialization magnet. The magneto-optical disk used in this reproducing method includes a reproducing layer, an intermediate layer, and a recording layer made of a rare earth-transition metal alloy. A front mask is formed in the low temperature region and a rear mask is formed in the high temperature region by utilizing the temperature distribution in the laser spot generated by rotating the medium and irradiating the reproducing laser beam. In the intermediate temperature region, the magnetization direction of the recording layer is transferred to the reproducing layer.
[0006]
When the magneto-optical output of the magneto-optical disk is detected, the magneto-optical signal is not read out because the mask is formed in the low-temperature region and the high-temperature region in the laser spot, and only from the intermediate temperature region. Can be read out. As described above, in the magneto-optical disk proposed by the applicant of the present application, a recording mark can be formed from an area substantially smaller than the beam spot by applying a magnetic field of several hundred Oe during reproduction without providing a large initialization magnet. It can be read with high resolution.
[0007]
[Problems to be solved by the invention]
The track pitch of the current magneto-optical disk having a recording capacity of 640 MB on one side is 1.1 μm, and the shortest mark length of the recording mark recorded on this is 0.64 μm. In order to further increase the recording capacity and to record a capacity of 1.0 GB or more on one side of a 3.5 inch size, it is necessary to reproduce smaller recording marks with a narrower track pitch. For example, for 1 GB single side, the track pitch is 1.0 μm and the shortest mark length is 0.43 μm. For 1.1 GB, the track pitch is 1.0 μm, the shortest mark length is 0.41 μm, and for 1.2 GB, the track pitch is 0.95 μm. , The shortest mark length is 0.38μm. Further, in order to realize a recording capacity of 1.3 GB, it is necessary to be able to reproduce a recording mark having a minimum length of 0.38 μm with a track pitch of 0.9 μm.
[0008]
When a capacity of 1.0 GB or more as described above is recorded on the above-described magneto-optical disk capable of reproducing MSR, the mask formation state becomes unstable due to the narrow track pitch, and the recording layer, intermediate layer, Depending on the magnetic characteristics of the reproducing layer, there has been a problem that the recording power margin of jitter becomes low. In addition, the current magneto-optical drive has a maximum output magnetic field of about 300 Oe in order to reduce the size and reduce power consumption. However, depending on the magnetic characteristics of the recording layer, intermediate layer, and reproducing layer, a reproducing magnetic field higher than 300 Oe is required. There was a case. Furthermore, depending on the magnetic characteristics of the recording layer, intermediate layer, and reproducing layer, there has been a problem that the quality of the reproduced signal is likely to deteriorate and the durability is lowered when information recorded at high density is repeatedly recorded / reproduced. .
[0009]
The present invention has been made in view of such circumstances, and by providing a magnetic film having a predetermined range of saturation magnetization and by providing a magnetic film having a predetermined range of Curie temperature, a single-sided surface of 3.5 inches can be obtained. It is an object of the present invention to provide a magneto-optical recording medium capable of reproducing information recorded at a density higher than GB with a magnetic power of 300 Oe or less and having a recording power margin of a practical level of jitter and super-resolution. To do. It is another object of the present invention to provide a high-density recorded magneto-optical recording medium having high durability against repeated recording / reproduction. It is another object of the present invention to provide a magneto-optical recording medium having desired magnetic characteristics by defining the magnetic film not by elemental composition but by saturation magnetization.
[0010]
[Means for Solving the Problems]
The magneto-optical recording medium according to the first invention comprises a magnetic laminated film comprising at least a reproducing layer, an intermediate layer and a recording layer. Preparation The reproducing layer and the recording layer are magnetic films having easy magnetization characteristics in the stacking direction, and the intermediate layer is a magnetic film having easy magnetization characteristics in the in-plane direction at room temperature. In a magneto-optical recording medium capable of reading The reproducing layer and the recording layer are each made of a rare earth transition metal containing GdFeCo and TbFeCo, and the intermediate layer is made of a rare earth transition metal containing GdFeCo selected from the group consisting of Si, Al and Cr. The magnetic multilayer film is formed on a substrate having a groove portion and a land portion, and the groove portion or the land portion has a width dimension of 0.72 μm to 0.76 μm and is approximately 0.9 μm. Formed with a track pitch, The reproducing layer, the intermediate layer, and the recording layer have a saturation magnetization of 8 emu / cc to 100 emu / cc, 140 emu / cc to 250 emu / cc, and 50 emu / cc to 150 emu / cc, respectively, at room temperature. And Curie temperatures of 240 ° C. to 350 ° C., 160 ° C. to 220 ° C. and 240 ° C. to 350 ° C. And a mask is formed by the saturation magnetization of the intermediate layer and the recording layer in the low temperature region generated by the laser light irradiation, and a mask is formed by the saturation magnetization of the reproducing layer in the high temperature region generated by the laser light irradiation. It is characterized by having a configuration.
[0011]
In the first invention, by specifying the saturation magnetization ranges of the reproducing layer, the intermediate layer, and the recording layer, it is possible to reproduce the high-density recorded MSR medium by applying a reproducing magnetic field of 300 Oe or less. The front mask formed in the low temperature region during reproduction is related to the saturation magnetization of the intermediate layer and the recording layer, and the rear mask formed in the high temperature region is related to the saturation magnetization of the reproduction layer. In each magnetic film, the saturation magnetization value at which a mask on each side can be formed with a reproducing magnetic field of 300 Oe or less is the lower limit. Further, the saturation magnetization value that does not deteriorate the reproduction quality even when repeatedly recorded / reproduced is the upper limit value.
[0012]
In addition, the magnitude of the reproducing magnetic field for forming the front mask during reproduction is related to the saturation magnetization of the recording layer. By specifying the saturation magnetization range of the recording layer, the front mask can be formed even with a small reproducing magnetic field. In addition, since the formation of the front mask greatly affects the reproduction of fine recording marks, the magnitude of the reproducing magnetic field for MSR reproduction can be adjusted by adjusting the saturation magnetization of the recording layer.
[0014]
Also By limiting the range of the Curie temperature of the reproducing layer, the intermediate layer, and the recording layer, it is possible to reproduce an MSR medium on which high density recording has been performed, using an existing magneto-optical drive. The Curie temperature range of each magnetic layer is determined in consideration of the power limit of the light source provided in the magneto-optical drive, enabling the formation of a double mask with a reproducing magnetic field of 300 Oe or less, and obtaining a sufficient reproducing power margin. Yes.
[0016]
Also By adding a nonmagnetic metal to the intermediate layer, the Curie temperature of the intermediate layer can be lowered while maintaining other magnetic properties.
[0017]
First 2 The magneto-optical recording medium according to the invention is: 1st invention The substrate further includes a substrate, a protective resin layer, and a heat conductive layer, and the reproduction layer, the intermediate layer, the recording layer, and the heat conductive layer are stacked in this order from the substrate side, and the outermost layers on both sides are the protective resin layers. It is characterized by being coated.
[0018]
First 2 In the invention, recording / reproduction is performed by irradiating the light beam from the substrate side of the magneto-optical recording medium. Heat is diffused in the in-plane direction of the medium by the heat conductive layer, and the durability of the magneto-optical recording medium is improved. Further, since a protective resin layer such as an ultraviolet curable resin layer is coated on both surfaces of the medium, wrinkles, abrasion, and the like from the outside are prevented with respect to the substrate and the magnetic layer, and durability is improved.
[0019]
First 3 The magneto-optical recording medium according to the invention is: 1st invention The substrate further includes a substrate, a protective resin layer, and a heat conductive layer. The heat conductive layer, the recording layer, the intermediate layer, and the reproduction layer are stacked in this order from the substrate side, and the outermost layers on both sides are the protective resin layers. It is characterized by being coated.
[0020]
First 3 In the invention, recording / reproduction is performed by irradiating the light beam from the side opposite to the substrate of the magneto-optical recording medium. Heat is diffused in the in-plane direction of the medium by the heat conductive layer, and the durability of the magneto-optical recording medium is improved. Further, since a protective resin layer such as an ultraviolet curable resin layer is coated on both surfaces of the medium, wrinkles, abrasion, and the like from the outside are prevented with respect to the substrate and the magnetic layer, and durability is improved.
[0021]
First 4 The magneto-optical recording medium according to the invention is 2 Or the second 3 In the present invention, the heat conductive layer has a thickness of 5 nm to 25 nm.
[0022]
First 4 In the invention, the thickness of the heat conductive layer is preferably 5 nm to 25 nm. For example, when AlTi is used as the heat conductive layer, the signal quality is not sufficient when it is formed thinner than 5 nm, and when AlCr is used as it is formed thicker than 25 nm, the recording power sensitivity tends to deteriorate.
[0023]
First 5 The magneto-optical recording medium according to the invention is 2 Or the second 4 In the present invention, a first dielectric layer is provided between the substrate and the reproducing layer, and a second dielectric layer is provided between the recording layer and the heat conductive layer, and the first dielectric layer has a thickness of 65 nm to The second dielectric layer has a thickness of 110 nm, and the second dielectric layer has a thickness of 20 nm to 60 nm.
[0024]
First 5 In the invention, the film thickness of the first dielectric layer is preferably 65 nm to 110 nm, and the film thickness of the second dielectric layer is preferably 20 nm to 60 nm. For example, when AlCr is used as the heat conductive layer, the signal quality is not sufficient when the first dielectric layer is formed thinner than 65 nm, and when AlTi is used as the heat conductive layer, the first dielectric layer is not formed. If it is formed thicker than 110 nm, the recording power sensitivity tends to deteriorate. Even if the heat conductive layer is either AlCr or AlTi, if the second dielectric layer is thinner than 20 nm, the environmental durability is not sufficient, and if it is thicker than 60 nm, the recording power sensitivity tends to deteriorate. It is in.
[0025]
First 6 The magneto-optical recording media according to the present invention are first to second. 5 In any of the invention ,in front It is characterized in that a recording mark is formed on the land portion.
[0026]
First 6 In the invention, the recording mark is formed in the land portion, and the groove portion is used for tracking control. In such a land-recording magneto-optical recording medium, even when the track pitch is as narrow as 0.85 μm to 0.9 μm, a front mask and a rear mask can be formed by applying a low reproducing magnetic field of 300 Oe or less, and high-density recording is performed. Information on the MSR medium can be reproduced.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing the film configuration of the magneto-optical disk of the present invention. The magneto-optical disk 1 includes a substrate 12 made of polycarbonate, a base dielectric layer 13 made of SiN, a reproduction layer 14 made of GdFeCo, an intermediate layer 15 made of GdFeCoSi, a recording layer 16 made of TbFeCo, and an upper dielectric made of SiN. The body layer 17 and the heat conductive layer 18 made of AlCr are sequentially laminated. The outermost layers on both surfaces of the magneto-optical disk 1, that is, the surfaces of the substrate 12 and the heat conductive layer 18 are the first and second layers. Are coated with ultraviolet curable films 11 and 19.
[0030]
The substrate 12 is a land substrate having a groove for tracking. The land portion is formed with a track size of 3.5 inches in diameter, a thickness of 1.2 mm, a depth of the groove of 67 nm, and 0.9 μm. Is 0.73 μm. Here, the depth of the groove is λ / (6.5 n) nm (λ is the wavelength of the laser beam, λ = 685 nm, n is the refractive index of the substrate, n = 1.58), and the land width is the groove It is the half width for the depth.
[0031]
The reproduction layer 14 is a Gd24.6Fe61.8Co13.6 film having a thickness of 41 nm, has transition metal magnetization dominance (hereinafter referred to as TM rich), and has an easy axis in the vertical direction, that is, the stacking direction. The value of saturation magnetization at room temperature (10 ° C. to 35 ° C.) is lower than 100 emu / cc and increases with temperature up to around 170 ° C. The Curie temperature is approximately 270 ° C., and the coercive force at room temperature is within 1.5 kOe.
[0032]
The intermediate layer 15 is a (Gd33.8Fe62.4Co3.8) 92Si8 film having a thickness of 41 nm, and is a rare earth magnetization dominant (hereinafter referred to as RE-rich) in which no compensation temperature is seen up to the Curie temperature, and room temperature (10 ° C. to 35 ° C. ) Has an easy axis in the in-plane direction, and the easy axis changes from the in-plane direction to the vertical direction at a predetermined temperature higher than room temperature. The value of saturation magnetization at room temperature is within 250 emu / cc, and decreases monotonically to a Curie temperature of approximately 180 ° C. In order to set the Curie temperature low, the non-magnetic element Si is added to the intermediate layer 15. An element such as Al or Cr may be added instead of Si.
[0033]
The recording layer 16 is a Tb22.2Fe60.3Co17.5 film having a thickness of 50 nm, is TM rich, and has an easy magnetization axis in the perpendicular direction. The value of saturation magnetization at room temperature is within 150 emu / cc and increases with temperature up to about 150 ° C. The Curie temperature is approximately 270 ° C., and the coercive force at room temperature is 10 kOe or more. When the Curie temperatures of the reproducing layer 14, the intermediate layer 15, and the recording layer 16 are Tc1, Tc2, and Tc3, respectively, the relationship of Tc2 <Tc1, Tc2 <Tc3 is satisfied. Further, when the coercive force at room temperature of the reproducing layer 14 and the recording layer 16 is Hc1 and Hc3, the relationship of Hc3> Hc1 is satisfied.
[0034]
The underlying dielectric layer 13 has a thickness of 70 nm, the upper dielectric layer 17 has a thickness of 25 nm, and the heat conductive layer 18 has a thickness of 15 nm. These laminated films are sequentially formed by DC sputtering. Table 1 shows the sputtering conditions. The reproducing layer 14, the intermediate layer 15, and the recording layer 16 are set in advance with a film forming apparatus and film forming conditions so as to have the above-described value of saturation magnetization. Further, the lifetime of the target is also tested in advance, and is set so that the magnetic film having the saturation magnetization value described above is reliably formed.
[0035]
[Table 1]

[0036]
Random data with the shortest mark length of 0.38 μm was optically modulated and recorded on the magneto-optical disk 1 having the above-described film structure, and reproduced and evaluated at a linear velocity of 7.5 m / s. During reproduction, a reproducing magnetic field in the same direction as the recording direction of the recording mark was applied at 300 Oe. The reproduction laser beam was irradiated from the substrate 12 side of the magneto-optical disk 1. FIG. 2 is a diagram showing the film configuration of the magneto-optical disk of FIG. 1 and the magnetization state during reproduction. Only the reproducing layer, intermediate layer and recording layer are shown, and the other film layers are omitted. As shown in FIG. 2, when the magneto-optical disk 1 rotates and a reproducing laser beam is irradiated onto the magnetic layer, a temperature distribution is generated. In the low temperature region, when the reproducing magnetic field is larger than the exchange coupling force acting between the intermediate layer 15 and the recording layer 16, the magnetization direction of the intermediate layer 15 is aligned with the reproducing magnetic field. The magnetization direction of the reproducing layer 14 exchange-coupled to the intermediate layer 15 is aligned in the opposite direction to the reproducing magnetic field regardless of the recording mark, thereby forming a front mask. In the high temperature region, the exchange coupling force acting between the reproducing layer 14 and the intermediate layer 15 is cut, and the rear mask is formed by aligning the magnetization direction of the reproducing layer in the same direction as the reproducing magnetic field. In the intermediate temperature region, an exchange coupling force larger than the reproducing magnetic field is applied between the reproducing layer 14, the intermediate layer 15, and the recording layer 16, and the magnetization direction of the recording layer 16 is transferred to the reproducing layer 14.
[0037]
When the magneto-optical output of the magneto-optical disk 1 is detected in this way, the magneto-optical signal is not read out because the mask is formed in the low temperature region and the high temperature region in the laser spot, and only in the intermediate temperature region. Can read a magneto-optical signal.
[0038]
FIG. 3 is a graph showing the recording power margin of jitter of the magneto-optical disk 1. The vertical axis represents random jitter, and the horizontal axis represents the recording power of laser light. In practice, the random jitter is preferably 12.5% or less. From the graph, it can be seen that the recording power margin of jitter of the magneto-optical disk 1 is ± 11%. This is a practically sufficient value.
[0039]
Thus, since the magneto-optical disk 1 of Embodiment 1 has a track pitch of 0.9 μm and a shortest recording mark of 0.38 μm, reproduction of a high-density recording magneto-optical disk having a recording capacity of 1.3 GB is sufficient. It can be said that it was realized with a recording power margin of a large jitter.
[0040]
The magnetic characteristics of the magnetic film capable of MSR reproduction of information recorded at high density on the magneto-optical disk having the film structure as described above were examined. First, the saturation magnetization range of each magnetic layer that can be reproduced by applying a reproduction magnetic field of 300 Oe was examined. FIG. 4 is a graph showing the change in the required reproducing magnetic field for forming the rear mask depending on the composition of the reproducing layer. The vertical axis represents the reproducing magnetic field Hrear necessary for forming the rear mask, and the horizontal axis represents the saturation magnetization Ms1 of the reproducing layer. From the graph, it can be seen that the saturation magnetization Ms1 of the reproducing layer 14 needs to be 8 emu / cc or more in order to reproduce with a magnetic field within 300 Oe.
[0041]
As the saturation magnetization of the reproduction layer 14 increases, the degree of quality degradation of the reproduction signal increases. FIG. 5 is a graph showing the relationship between the saturation magnetization of the reproduction layer and the reproduction signal quality. The vertical axis represents ΔCNR, which is the difference from the reference CNR, and the horizontal axis represents the saturation magnetization Ms1 of the reproducing layer. ΔCNR measures the degree of signal quality degradation when erasing 100,000 times continuously with an erasing power that is approximately 13% higher than the optimum recording power. From the graph, it can be seen that the saturation magnetization Ms1 of the reproducing layer 14 is 100 emu / cc or less within 1 dB which is the allowable range of ΔCNR.
[0042]
FIG. 6 is a graph showing a change in the necessary reproducing magnetic field for forming the front mask depending on the composition of the intermediate layer. The vertical axis represents the reproducing magnetic field Hfront necessary for forming the front mask, and the horizontal axis represents the saturation magnetization Ms2 of the intermediate layer. From the graph, it can be seen that the saturation magnetization Ms2 of the intermediate layer 15 requires a value of 140 emu / cc or more in order to reproduce with a magnetic field within 300 Oe. FIG. 7 is a graph showing the relationship between the saturation magnetization of the intermediate layer and the reproduction signal quality. The vertical axis represents ΔCNR, which is the difference from the reference CNR, and the horizontal axis represents the saturation magnetization Ms2 of the intermediate layer. ΔCNR measures the degree of signal quality degradation when erasing 100,000 times continuously with an erasing power that is approximately 13% higher than the optimum recording power. From the graph, it can be seen that the saturation magnetization Ms2 of the intermediate layer 15 is 250 emu / cc or less within 1 dB which is the allowable range of ΔCNR.
[0043]
FIG. 8 is a graph showing a change in the necessary reproducing magnetic field for forming the front mask depending on the composition of the recording layer. The vertical axis represents the reproducing magnetic field Hfront necessary for forming the front mask, and the horizontal axis represents the saturation magnetization Ms3 of the recording layer. From the graph, it can be seen that the saturation magnetization Ms3 of the recording layer 16 requires a value of 50 emu / cc or more in order to reproduce with a magnetic field within 300 Oe. FIG. 9 is a graph showing the relationship between the saturation magnetization of the recording layer and the reproduction signal quality. The vertical axis represents ΔCNR, which is the difference from the reference CNR, and the horizontal axis represents the saturation magnetization Ms3 of the recording layer. ΔCNR measures the degree of signal quality degradation when erasing 100,000 times continuously with an erasing power that is approximately 13% higher than the optimum recording power. From the graph, it can be seen that the saturation magnetization Ms3 of the recording layer 16 is 150 emu / cc or less within 1 dB which is the allowable range of ΔCNR.
[0044]
From the above, the saturation magnetization range of each magnetic layer capable of reproducing a magneto-optical disk having a recording capacity of about 1.3 GB by applying a reproducing magnetic field of 300 Oe or less is 8 emu / cc to 100 emu / It can be said that the intermediate layer 15 is 140 emu / cc to 250 emu / cc, and the recording layer 16 is 50 emu / cc to 150 emu / cc. The magneto-optical disk 1 according to Embodiment 1 described above satisfies this condition.
[0045]
Next, the range of the Curie temperature of each magnetic layer that can be reproduced using the current magneto-optical drive was examined. FIG. 10 is a graph showing the sensitivity of the recording power at room temperature, which varies with the Curie temperature of the recording layer. This is the value at the outermost circumference of 3.5 inches. The vertical axis represents the recording power of the laser beam, and the horizontal axis represents the Curie temperature Tc3 of the recording layer 16. The recording power sensitivity indicates both the power Pwth at which a signal starts to appear and the power Pw at which a signal can be sufficiently obtained. FIG. 11 is a graph showing the relationship between the ambient temperature of the magneto-optical disk and the recording power. The vertical axis indicates the recording power, and the horizontal axis indicates the environmental temperature. It is a measurement result at a linear velocity of 12.6 m / s. From FIG. 11, it can be seen that the lower the environmental temperature, the higher the recording power required.
[0046]
As shown in FIG. 10, when the power limit of the laser diode of the magneto-optical drive is about 13 mW, it can be said that the Curie temperature Tc3 is allowed up to 450 ° C. with respect to the recording power Pwth. Since the obtained recording power is used and, as shown in FIG. 11, a higher recording power is required to guarantee the operation up to the ambient temperature of 0 ° C., the Curie temperature Tc3 of the recording layer 16 is 350. It can be said that the upper limit is ° C.
[0047]
FIG. 12 is a graph showing the reproduction power sensitivity that changes with respect to the Curie temperature of the intermediate layer. The vertical axis represents the reproduction power of the laser beam, and the horizontal axis represents the Curie temperature Tc2 of the intermediate layer 15. The reproduction power sensitivity indicates the case where the ambient temperature is 0 ° C. and 25 ° C. with respect to the power Prth at which a signal starts to be output, and also shows the power Pr that can sufficiently obtain a signal at 0 ° C. As can be seen from the graph, higher reproduction power is required at 0 ° C. than at 25 ° C. Actually, the reproduction power Pr at which a sufficient signal can be obtained shows a higher value. When the limit of high frequency superposition is 6.4 mW, the upper limit of the Curie temperature Tc2 of the intermediate layer 15 is 220 ° C.
[0048]
FIG. 13 is a graph showing the relationship between the easy axis characteristics of the intermediate layer and the reproducing magnetic field. The vertical axis represents the reproducing magnetic field, and the horizontal axis represents the temperature at which the intermediate layer 15 changes from in-plane magnetization to perpendicular magnetization. As can be seen from the graph, the value of the reproducing magnetic field decreases as the temperature at which the intermediate layer changes to perpendicular magnetization becomes higher. It can be seen that in order to reproduce with a reproducing magnetic field of 300 Oe or less, the temperature changed to perpendicular magnetization needs to be 130 ° C. or more. FIG. 14 is a graph showing the relationship between the Curie temperature of the intermediate layer and the easy axis characteristics. The vertical axis represents the temperature at which the intermediate layer 15 changes from in-plane magnetization to perpendicular magnetization, and the horizontal axis represents the Curie temperature Tc2 of the intermediate layer 15. From the graph, it can be seen that the Curie temperature Tc2 of the intermediate layer 15 where the temperature changing to the perpendicular magnetization is 130 ° C. or higher is 160 ° C. or higher.
[0049]
When the Curie temperature Tc2 of the intermediate layer 15 is 160 ° C. or higher, the reproduction power Prth is about 4.1 mW or higher as shown in FIG. In order to secure a sufficient reproduction power margin of about ± 20% from when the reproduction signal is seen until it starts to disappear, when the reproduction signal starts to appear from 4.1 mW, the reproduction power Peth that begins to disappear becomes 6.2 mW. FIG. 15 is a graph showing the relationship between the Curie temperature of the recording layer and the power of the laser beam. The vertical axis represents the power of the laser beam, and the horizontal axis represents the Curie temperature Tc3 of the recording layer 16. From the graph, it can be seen that when the reproduction power Peth is 6.2 mW or more, the Curie temperature Tc3 of the recording layer 16 needs to be 240 ° C. or more.
[0050]
Since the reproducing layer 14 needs to reproduce the recording mark formed on the recording layer 16, the range of the Curie temperature Tc1 of the reproducing layer 14 is the same as that of the recording layer 16, and is 240 ° C. to 350 ° C.
[0051]
From the above, the range of Curie temperature of each magnetic layer that can reproduce a magneto-optical disk having a recording capacity of about 1.3 GB using the current magneto-optical drive is 240 ° C. to 350 ° C. for the reproducing layer 14. The intermediate layer 15 is 160 ° C. to 220 ° C., and the recording layer 16 is 240 ° C. to 350 ° C. The magneto-optical disk 1 according to Embodiment 1 described above satisfies this condition.
[0052]
With respect to the magneto-optical disk of the comparative example having the magnetic layer outside the range of the saturation magnetization and the Curie temperature, the recording mark formed in the same manner as in the first embodiment was reproduced and evaluated. This magneto-optical disk is provided with the same substrate as in Embodiment 1, the reproducing layer 14 and the recording layer 16 have a compensation composition, that is, the value of the spontaneous magnetization Ms is almost zero, and the Curie temperature Tc2 of the intermediate layer 15 is 150 ° C. is there. FIG. 16 is a graph showing the recording power margin of jitter and the necessary reproducing magnetic field of the magneto-optical disk of the comparative example. The vertical axis represents random jitter, and the horizontal axis represents the recording power of laser light. In the graph, “◯” indicates the case where the reproducing magnetic field is 300 Oe, “Δ” indicates the case where 350 Oe, and “□” indicates the case where 400 Oe.
[0053]
The magneto-optical disk of the comparative example had high durability in repeated continuous erasure, and signal quality was hardly deteriorated even after erasing 100,000 times. However, the bottom jitter value is higher than that of the magneto-optical disk of the first embodiment (see FIG. 3). The recording power margin with random jitter of 12.5% or less was ± 8.3%, which was found to be narrower than that of the magneto-optical disk 1 of the first embodiment. Furthermore, the reproducing magnetic field could not be reproduced at 300 Oe, and 350 Oe or more was necessary.
[0054]
Embodiment 2. FIG.
A magneto-optical disk having the same film configuration as that of the first embodiment was formed using substrates having different track pitches, and a mark of 2T = 0.4 μm was recorded. The required reproducing magnetic field and CNR were examined for each magneto-optical disk. FIG. 17 is a graph showing the results. The vertical axis represents CNR and the required reproducing magnetic field Hrth, and the horizontal axis represents the track pitch. From the graph, it can be seen that the CNR tends to decrease as the track pitch becomes narrower. In particular, when the track pitch is narrower than 0.9 μm, it can be said that the CNR is deteriorated by 1.5 dB or more as compared with the case of 1.1 μm. The required reproducing magnetic field did not change greatly with respect to the track pitch.
[0055]
Next, magneto-optical disks having the same film configuration as in the first embodiment were formed using groove substrates having different track pitches, and the necessary reproducing magnetic field and CNR were similarly examined for each. FIG. 18 is a graph showing the results. The vertical axis represents CNR and the required reproducing magnetic field Hrth, and the horizontal axis represents the track pitch. When a groove substrate is used, it can be seen from the graph that although the CNR does not decrease from 1.1 μm to 0.85 μm, the required reproducing magnetic field rapidly increases below 0.9 μm. 17 and 18, it can be seen that the track pitch can be reduced to 0.9 μm in order to realize a recording capacity of 1 GB or more by using the magneto-optical disk having this film configuration. Further, it can be said that MSR reproduction is possible with a reproducing magnetic field of 300 Oe or less with a narrow track pitch by using a land substrate.
[0056]
In order to enable reproduction at a narrower track pitch, the necessary reproducing magnetic field was examined for each of the front mask and the rear mask using the above-described groove substrate. FIG. 19 is a graph showing the results. The vertical axis represents the required reproducing magnetic field, and the horizontal axis represents the track pitch. As is apparent from the graph, when the track pitch is narrower than 0.9 μm, the reproducing magnetic field necessary for forming the front mask increases rapidly. From this, it can be seen that the cause of the increase in the required reproducing magnetic field when the track pitch is narrowed is the formation of the front mask. Therefore, the composition of the recording layer 16 that can reduce the reproducing magnetic field for forming the front mask was examined. FIG. 20 is a graph showing the results. The vertical axis represents the reproducing magnetic field necessary for forming the front mask, and the horizontal axis represents the Tb content of the recording layer 16. In the graph, “◯” indicates a land substrate, and “×” indicates a groove substrate. From the graph, it can be seen that the composition range of the recording layer 16 that can be reproduced with a reproducing magnetic field of 300 Oe or less is narrower on the groove substrate than on the land substrate.
[0057]
18 to 20, it can be said that the land substrate is more suitable than the groove substrate for MSR reproduction using a reproducing magnetic field of 300 Oe or less at a narrow track pitch of about 0.9 μm. Further, even with a groove substrate, the above-described MSR reproduction can be performed by adjusting the Tb content of the recording layer 16, but it can be seen that the composition margin of the recording layer 16 is narrower for the groove substrate than for the land substrate. It was. From these facts, it can be understood that the magnitude of the necessary reproducing magnetic field can be adjusted by adjusting the saturation magnetization of the recording layer 16 in both the land substrate and the groove substrate. That is, MSR reproduction can be performed by setting the composition of the recording layer 16 according to the track pitch of the substrate and applying a reproducing magnetic field having a desired magnitude.
[0058]
Embodiment 3 FIG.
Magneto-optical disks similar to those in the first embodiment described above were formed by changing only the film thickness of the heat conductive layer 18 made of AlCr, and SNR was measured as recording power sensitivity and signal quality. As a result, when the thickness of the heat conductive layer 18 is 8 nm, the SNR is about 2 dB lower than that of the 20 nm layer, and therefore the minimum value of jitter does not show a sufficiently low value. Further, when the film thickness of the heat conductive layer 18 was 10 nm or more, the jitter was as low as that of the first embodiment (see FIG. 3). Further, when the thickness of the heat conductive layer 18 is 30 nm, the recording power sensitivity is about 2 mW lower than that of the 8 nm layer, so that reproduction using the current magneto-optical drive is difficult. From these facts, it is understood that the film thickness of the AlCr heat conduction layer 18 is preferably 10 nm to 25 nm.
[0059]
Further, even when an AlTi film was used as the heat conductive layer 18, the magneto-optical disk showed the same reproduction characteristics as in the first embodiment. Then, magneto-optical disks were formed by changing only the thickness of the AlTi film, and the recording power sensitivity and SNR with respect to the thickness were measured. As a result, when the thickness of the heat conductive layer 18 is 3 nm, the SNR is about 2 dB lower than that of the 15 nm layer, and therefore the jitter minimum value does not show a sufficiently low value. Further, when the thermal conductive layer 18 has a film thickness of 25 nm, the recording power sensitivity is about 2 mW lower than that of the 3 nm film, so that reproduction using the current magneto-optical drive is difficult. From these facts, it is understood that the thickness of the AlTi heat conduction layer 18 is preferably 5 nm to 20 nm. Therefore, it can be said that the optimum range of the film thickness of the heat conductive layer 18 of the magneto-optical disk according to the present invention is 5 nm to 25 nm.
[0060]
Embodiment 4 FIG.
The magneto-optical disk 1 similar to that of the first embodiment described above was formed by changing only the thickness of the base dielectric layer 13 made of SiN, and the reflectance, recording power sensitivity, and SNR were measured. As a result, the thickness of the underlying dielectric layer 13 in the vicinity of 75 nm showed a minimum reflectance. When the thickness of the underlying dielectric layer 13 is 60 nm, the SNR is about 1.6 dB lower than that of 90 nm, and when the thickness of the underlying dielectric layer 13 is 98 nm, the recording power sensitivity is higher than that of 60 nm. It deteriorated by about 1.5 mW. From these facts, it was found that the thickness of the underlying dielectric layer 13 of the magneto-optical disk 1 is preferably 65 nm to 95 nm. However, this range is the case where the heat conductive layer 18 is formed of an AlCr film. When the heat conductive layer 18 was formed of AlTi, a sufficient recording power was obtained when the thickness of the underlying dielectric layer 13 was 105 nm, which was outside the allowable range at 115 nm. Therefore, it can be said that the optimum range of the film thickness of the underlying dielectric layer 13 of the magneto-optical disk according to the present invention is 65 nm to 110 nm.
[0061]
Next, magneto-optical disks similar to those of the first embodiment were formed by changing only the film thickness of the upper dielectric layer 17 made of SiN, and recording power sensitivity and environmental temperature durability were measured. As a result, when the thickness of the upper dielectric layer 17 was 15 nm, defects such as corrosion occurred after 200 hours in an environment of a temperature of 80 ° C. and a humidity of 85%. Further, when the film thickness of the upper dielectric layer 17 was 65 nm, the recording power sensitivity was deteriorated by about 2 mW compared with the film having a thickness of 20 nm. From these facts, it can be said that the thickness of the upper dielectric layer 17 of the magneto-optical disk according to the present invention is preferably 20 nm to 60 nm.
[0062]
Embodiment 5 FIG.
A magneto-optical disk similar to that of the first embodiment described above was formed by changing only the substrate 12. The substrate of the fifth embodiment is a polycarbonate land substrate having a groove depth of 93 nm (λ / (4.4n) nm) and a land width of 0.75 μm. Other dimensions and configurations are the same as those in the first embodiment, and a description thereof will be omitted. Random jitter was evaluated for such a magneto-optical disk. FIG. 21 is a graph showing the results. The vertical axis represents random jitter, and the horizontal axis represents the recording power of laser light. From the graph, it can be seen that the recording power margin where the random jitter is 12.5% or less is ± 11%. Therefore, it can be seen that the jitter recording power margin of the magneto-optical disk of Embodiment 5 recorded with high density shows ± 11%. This is a practically sufficient value.
[0063]
Embodiment 6 FIG.
FIG. 22 is a sectional view showing the film configuration of the magneto-optical disk according to the sixth embodiment. The magneto-optical disk 2 is formed on a polycarbonate substrate 12, a heat conductive layer 18 made of AlCr, a base dielectric layer 13 made of SiN, a recording layer 16 made of TbFeCo, an intermediate layer 15 made of GdFeCoSi, and a reproducing layer 14 made of GdFeCo. And an upper dielectric layer 17 made of SiN. The outermost layers of the magneto-optical disk 2, that is, the surfaces of the substrate 12 and the upper dielectric layer 17 are the first and second ultraviolet rays. It is covered with cured films 11 and 19. The magneto-optical disk 2 is the same as the magneto-optical disk 1 shown in FIG. 1 except that the stacking order of the films is different. The magnetic characteristics and film thicknesses such as saturation magnetization and Curie temperature of each magnetic film and the substrate specifications are as follows. Description is omitted.
[0064]
Random data with the shortest mark length of 0.38 μm was optically modulated and recorded on the magneto-optical disk 2 having the above-described film structure, and reproduced and evaluated at a linear velocity of 7.5 m / s. During reproduction, a reproducing magnetic field in the same direction as the recording direction of the recording mark was applied at 300 Oe. Further, the reproduction laser beam was irradiated from the side far from the substrate 12, that is, the side near the reproduction layer 14. As a result, it has been found that reproduction of the high-density magneto-optical disk 2 having a recording capacity of 1.3 GB can be realized with a sufficient recording power margin of jitter as in the first embodiment.
[0065]
The reproducing layer, the intermediate layer, and the recording layer of the magneto-optical recording medium of the present invention are not limited to the magnetic films used in the magneto-optical disks of the first to sixth embodiments described above. With a magnetic film having magnetic characteristics in the above-described range, a medium recorded with a high density of 3.5 GB and a single side of 1.3 GB can be reproduced by MSR.
[0066]
【The invention's effect】
As described above, in the present invention, a magneto-optical recording medium is formed using a magnetic film having a saturation magnetization in a predetermined range, so that high-density recording with a track pitch of 0.9 μm and a shortest mark length of about 0.38 μm. The medium can be reproduced by MSR with a reproducing magnetic field of 300 Oe or less. In addition, since the magneto-optical recording medium is formed using a magnetic film having a Curie temperature within a predetermined range, reproduction using the existing magneto-optical drive is possible, and compatibility with the current medium can be maintained. . Further, such a magneto-optical recording medium is excellent in durability against repeated recording / reproduction. Furthermore, by forming the magnetic film so that the saturation magnetization thereof has a predetermined value, a magneto-optical recording medium having desired magnetic characteristics can be manufactured with good reproducibility, high-density recording / reproduction is ensured, etc. The present invention has an excellent effect.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a film configuration of a magneto-optical disk of the present invention.
FIG. 2 is a diagram showing a film configuration of a magneto-optical disk of the present invention and a magnetization state during reproduction.
3 is a graph showing a recording power margin of jitter of the magneto-optical disk of Embodiment 1. FIG.
FIG. 4 is a graph showing the relationship between the saturation magnetization of the reproducing layer and the necessary reproducing magnetic field for mask formation.
FIG. 5 is a graph showing the relationship between the saturation magnetization of the reproduction layer and the reproduction signal quality.
FIG. 6 is a graph showing the relationship between the saturation magnetization of the intermediate layer and the necessary reproducing magnetic field for mask formation.
FIG. 7 is a graph showing the relationship between the saturation magnetization of the intermediate layer and the reproduction signal quality.
FIG. 8 is a graph showing the relationship between the saturation magnetization of the recording layer and the necessary reproducing magnetic field for mask formation.
FIG. 9 is a graph showing the relationship between the saturation magnetization of the recording layer and the reproduction signal quality.
FIG. 10 is a graph showing the relationship between the Curie temperature of the recording layer and the recording power.
FIG. 11 is a graph showing the relationship between the environmental temperature and recording power of a magneto-optical disk.
FIG. 12 is a graph showing the relationship between the Curie temperature of the intermediate layer and the reproduction power.
FIG. 13 is a graph showing the relationship between the easy axis characteristics of the intermediate layer and the reproducing magnetic field.
FIG. 14 is a graph showing the relationship between the Curie temperature of the intermediate layer and the easy axis characteristics.
FIG. 15 is a graph showing the relationship between the Curie temperature of the recording layer and the power of the laser beam.
FIG. 16 is a graph showing a recording power margin of jitter and a necessary reproducing magnetic field in a comparative example.
FIG. 17 is a graph showing the reproduction characteristics and the necessary reproduction magnetic field with respect to the track pitch of the land recording disk of the second embodiment.
FIG. 18 is a graph showing the reproduction characteristics and the necessary reproduction magnetic field with respect to the track pitch of the groove recording disk of the second embodiment.
FIG. 19 is a graph showing the relationship of the necessary reproducing magnetic field for mask formation with respect to the track pitch in the second embodiment.
20 is a graph showing the relationship between the recording layer of Embodiment 2 and the necessary reproducing magnetic field for mask formation. FIG.
FIG. 21 is a graph showing a recording power margin of jitter of the magneto-optical disk according to the fifth embodiment.
22 is a cross-sectional view showing a film configuration of a magneto-optical disk according to Embodiment 6. FIG.
[Explanation of symbols]
1, 2 magneto-optical disk
11, 19 UV cured film
12 Substrate
13 Underlying dielectric layer
14 Playback layer
15 Middle layer
16 Recording layer
17 Upper dielectric layer
18 Thermal conduction layer

Claims (6)

At least reproducing layer, an intermediate layer and a recording layer magnetic laminated film by laminating, the reproducing layer and the recording layer are magnetic films having an easy magnetization characteristic in the stacking direction, the intermediate layer plane direction of easy magnetization at room temperature In a magneto-optical recording medium, which is a magnetic film having characteristics, and capable of reading a magneto-optical signal by irradiation with a reproduction laser beam,
The reproducing layer and the recording layer are each formed of a rare earth transition metal containing GdFeCo and TbFeCo,
The intermediate layer includes a non-magnetic metal selected from the group consisting of Si, Al, and Cr in the rare earth transition metal including GdFeCo,
The magnetic laminated film is formed on a substrate having a groove portion and a land portion, and the groove portion or the land portion has a width dimension of 0.72 μm to 0.76 μm and is formed with a track pitch of about 0.9 μm. The reproducing layer, the intermediate layer, and the recording layer have a saturation magnetization of 8 emu / cc to 100 emu / cc, 140 emu / cc to 250 emu / cc, and 50 emu / cc to 150 emu / cc, respectively , and 240 ° C. to 350 at room temperature. And a Curie temperature of 160 ° C. to 220 ° C. and 240 ° C. to 350 ° C., and a mask is formed by saturation magnetization of the intermediate layer and the recording layer in a low temperature region generated by the laser light irradiation. A magneto-optical recording medium characterized in that a mask is formed by saturation magnetization of the reproducing layer in a high temperature region generated by irradiation. Furthermore, a substrate, a protective resin layer, and a heat conductive layer are provided, and the reproduction layer, the intermediate layer, the recording layer, and the heat conductive layer are laminated in this order from the substrate side, and the outermost layers on both sides are covered with the protective resin layer. The magneto-optical recording medium according to claim 1, wherein Further, a substrate, a protective resin layer, and a heat conductive layer are provided, and the heat conductive layer, the recording layer, the intermediate layer, and the reproducing layer are laminated in this order from the substrate side, and the outermost layers on both sides are covered with the protective resin layer. The magneto-optical recording medium according to claim 1, wherein The thermally conductive layer is a magneto-optical recording medium according to claim 2 or 3, wherein the has a thickness of 5 nm to 25 nm. A first dielectric layer is provided between the substrate and the reproducing layer, and a second dielectric layer is provided between the recording layer and the heat conductive layer, and the first dielectric layer is a film having a thickness of 65 nm to 110 nm. has a thickness, said second dielectric layer is a magneto-optical recording medium according to claim 2 or 4, wherein the film having a thickness of 20 nm to 60 nm. Magneto-optical recording medium according to any one of claims 1 to 5, characterized in that are no to form a recording mark before Symbol land portion.

Images