Multilayered magnetooptical recording medium

Claim 2

A magnetooptical recording medium having at least a first layer and a second layer which is laminated on the first layer and which satisfies the following formulas at room temperature: ##EQU10## where, H c1 : the coercivity of first layer H c2 : the coercivity of second layer M s1 : the saturation magnetic moment of first layer M s2 : the saturation magnetic moment of second layer t 1 : the film thickness of first layer t 2 : the film thickness of second layer T r : room temperature T c1 : the Curie temperature of first layer T c2 : the Curie temperature of second layer σ w : the interface magnetic wall energy between the first layer and the second layer.

Claim 3

A multilayered magnetooptical recording medium comprising a first layer as a recording layer and a second layer as an auxiliary reference layer, wherein said first and second layers are magnetically coupled and the magnetization direction of said reference layer is capable of being oriented in a predetermined direction without changing the magnetization direction of said recording layer, and wherein the oriented state of the magnetization direction of said reference layer is maintained at room temperature in a condition in which an external magnetic field is zero.

Claim 4

A multilayered magnetooptical recording medium comprising a first layer as a recording layer and a second layer as an auxiliary reference layer, wherein said first and second layers are magnetically coupled and the magnetization direction of said reference layer is capable of being oriented in a predetermined direction without changing the magnetization direction of said recording layer, and wherein the oriented state of the magnetization direction of said reference layer is maintained at room temperature in a condition in which an external magnetic field is zero.

Claim 5

An over-write capable multilayered magnetooptical recording medium comprising a first layer as a recording layer and a second layer as an auxiliary reference layer, wherein said first and second layers are magnetically coupled and the magnetization direction of said reference layer is capable of being oriented in a predetermined direction without changing the magnetization direction of said recording layer, and wherein the oriented state of the magnetization direction of said reference layer is maintained at room temperature in a condition in which an external magnetic field is zero.

Claim 6

An over-write capable multilayered magnetooptical recording medium comprising a first layer as a recording layer and a second layer as an auxiliary reference layer, wherein said first and second layers are magnetically coupled and the magnetization direction of said reference layer is capable of being oriented in a predetermined direction without changing the magnetization direction of said recording layer, and wherein the oriented state of the magnetization direction of said reference layer is maintained at room temperature in a condition in which an external magnetic field is zero.

Claim 7

A medium according to claim 2 or 3, wherein said first layer is a thin magnetic film having a high coercivity at room temperature and a low Curie temperature and said second layer is a thin magnetic film having a lower coercivity at room temperature and a higher Curie temperature than said first layer.

Claim 8

A medium according to claim 2 or 3, wherein when a temperature at which said first and second layers are magnetically coupled is given by T s1 , and a temperature at which the direction of magnetization of said second layer is reversed by a bias field is given by T s2 , said first layer has a higher coercivity at room temperature, said second layer has a lower coercivity at room temperature, and T S1 <T S2 .

Claim 9

A medium according to claim 2 or 3, wherein both said first and second layers consist of a material selected from transition metal-heavy rare earth metal alloy compositions.

Claim 10

A medium according to claim 2 or 3, wherein both said first and second layers consist of a material selected from transition metal-heavy rare earth metal alloy compositions.

Claim 11

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <Tcomp.1<T.sub.c1 ≈T.sub.L ≈Tcomp.2<T.sub.c2 ≈T.sub.H ( 1) and satisfies the following formulas at room temperature: H.sub.c1 >H.sub.c2 +(σ.sub.w /2M.sub.s1 t.sub.1)+(σ.sub.w /2M.sub.s2 t.sub.2) (2) H.sub.c1 >(σ.sub.w /2M.sub.s1 t.sub.1) (3) H.sub.c2 >(σ.sub.w /2M.sub.s2 t.sub.2) (4) H.sub.c2 +(σ.sub.w /2M.sub.s2 t.sub.2)<|Hini.|<H.sub.c1 -(σ.sub.w /2M.sub.s1 t.sub.1) (5) where T R : room temperature Tcomp.1: compensation temperature of first layer Tcomp.2: compensation temperature of second layer T c1 : Curie temperature of first layer T c2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H c1 : coercivity of first layer H c2 : coercivity of second layer M s1 : saturation magnetization of first layer M s2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 12

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.c1 ≈T.sub.L ≈Tcomp.2<T.sub.c2 ≈T.sub.H ( 1) and satisfies the following formulas at room temperature: H.sub.c1 >H.sub.c2 +(σ.sub.w /2M.sub.s1 t.sub.1)+(σ.sub.w /2M.sub.s2 t.sub.2) (2) H.sub.c1 >(σ.sub.w /2M.sub.s1 t.sub.1) (3) H.sub.c2 >(σ.sub.w /2M.sub.s2 t.sub.2) (4) H.sub.c2 +(σ.sub.w /2M.sub.s2 t.sub.2)<|Hini.|<H.sub.c1 -(σ.sub.w /2M.sub.s1 t.sub.1) (5) where T R : room temperature Tcomp.2: compensation temperature of second layer T c1 : Curie temperature of first layer T c2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H c1 : coercivity of first layer H c2 : coercivity of second layer M s1 : saturation magnetization of first layer M s2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 13

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <Tcomp.1<T.sub.c1 ≈T.sub.L <T.sub.c2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.c1 H.sub.c2 +(σ.sub.w /2M.sub.s1 t.sub.1)+(σ.sub.w /2M.sub.s2 t.sub.2) (2) H.sub.c1 >(σ.sub.w /2M.sub.s1 t.sub.1) (3) H.sub.c2 >(σ.sub.w /2M.sub.s2 t.sub.2) (4) H.sub.c +(σ.sub.w /2M.sub.s2 t.sub.2)<|Hini.|<H.sub.c1 -(σ.sub.w /2M.sub.s1 t.sub.1) (5) where T R : room temperature Tcomp.1: compensation temperature of first layer T c1 : Curie temperature of first layer T c2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H c1 : coercivity of first layer H c2 : coercivity of second layer M s1 : saturation magnetization of first layer M s2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 14

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.c1 ≈T.sub.L <T.sub.c2 <T.sub.H ( 1) and satisfies the following formulas at room temperature: H.sub.C1 >H.sub.C2 +(σ.sub.w /2M.sub.S1 t.sub.1)+(σ.sub.w /2M.sub.S2 t.sub.2) (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S2 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 -(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T r : room temperature T C : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coercivity of first layer H C2 : coercivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 15

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <Tcomp.1<T.sub.C1 ≈T.sub.L <T.sub.C2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.C1 >H.sub.C2 +|(σ.sub.w /2M.sub.S1 t.sub.1)-(σ.sub.w /2M.sub.S2 t.sub.2)| (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S2 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 +(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T R : room temperature Tcomp.1: compensation temperature of first layer T C1 : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coercivity of first layer H C2 : coercivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 16

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.C1 ≈T.sub.L <T.sub.C2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.C1 >H.sub.C2 +|(σ.sub.w /2M.sub.S1 t.sub.1)-(σ.sub.w /2M.sub.S2 t.sub.2)| (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S2 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 +(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T R : room temperature T C1 : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coercivity of first layer H C2 : coercivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 17

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.C1 ≈T.sub.L <T.sub.C2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.C1 >H.sub.C2 +(σ.sub.w /2M.sub.S1 t.sub.1)+(σ.sub.w /2M.sub.S2 t.sub.2) (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S1 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 -(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T R : room temperature T C1 : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coercivity of first layer H C2 : coercivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 18

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has a compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.C1 ≈T.sub.L =Tcomp.2<T.sub.C2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.C1 H.sub.C2 +|(σ.sub.w /2M.sub.S1 t.sub.1)-(σ.sub.w /2M.sub.S2 t.sub.2)| (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S2 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 +(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T R : room temperature Tcomp.2: compensation temperature of second layer T C1 : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coersivity of first layer H C2 : coersivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 19

A medium according to claim 2 or 3, wherein said first layer consists of a transition metal-heavy rare earth metal alloy, which is transition metal rich and has no compensation temperature between room temperature and a Curie temperature, and said second layer consists of a transition metal-heavy rare earth metal alloy, which is heavy rare earth metal rich and has no compensation temperature between room temperature and a Curie temperature, and which satisfies the following formula: T.sub.R <T.sub.C1 ≈T.sub.L <T.sub.C2 ≈T.sub.H( 1) and satisfies the following formulas at room temperature: H.sub.C1 >H.sub.C2 +|(σ.sub.w /2M.sub.S1 t.sub.1)-(σ.sub.w /2M.sub.S2 t.sub.2)| (2) H.sub.C1 >(σ.sub.w /2M.sub.S1 t.sub.1) (3) H.sub.C2 >(σ.sub.w /2M.sub.S2 t.sub.2) (4) H.sub.C2 +(σ.sub.w /2M.sub.S2 t.sub.2)<|Hini.|<H.sub.C1 +(σ.sub.w /2M.sub.S1 t.sub.1) (5) where T R : room temperature T C1 : Curie temperature of first layer T C2 : Curie temperature of second layer T L : temperature of recording medium when irradiated with low-level laser beam T H : temperature of recording medium when irradiated with high-level laser beam H C1 : coercivity of first layer H C2 : coercivity of second layer M S1 : saturation magnetization of first layer M S2 : saturation magnetization of second layer t 1 : film thickness of first layer t 2 : film thickness of second layer σ w : interface wall energy Hini.: initial field.

Claim 20

A medium according to claim 2 or 3, wherein a direction of magnetization of said reference layer in at least a part of the medium orients to an A-direction.

Claim 21

A multilayered magnetooptical recording medium according to claim 17, wherein after a beam of high intensity level is radiated to said part of the medium, which is moving under a bias magnetic field, a bit having a non-A-direction magnetization is formed in said reference layer and a bit having a direction of magnetization controlled by said reference layer is formed in said recording layer, and after a beam of low intensity level is radiated to said part of the medium which is moving, a bit having an A-direction magnetization is formed in said reference layer and a bit having a direction of magnetization controlled by said reference layer is formed in said recording layer.