Magnetooptical recording medium allowing overwriting with two or more magnetic layers and recording method utilizing the same

Claim 2

A magnetooptical recording medium according to Claim I, wherein said first and second magnetic layers are both composed of alloys of a rare earth element and a transition metal, and one of said alloys has a composition rich in the rare earth element compared with the compensation composition, while the other has a composition rich in the transition metal compared with the compensation composition.

Claim 3

A magnetooptical recording medium according to Claim I, wherein said first and second magnetic layers are composed of alloys selected from GdCo, GdFe, TbFe, DyFe, GdTbFe, TbDyFe, GdFeCo, TbFeCo, GdTbCo, and GdTbFeCo.

Claim 4

A magnetooptical recording medium according to Claim I, which comprises satisfying following relations: wherein L 1 is the thickness of said first magnetic layer, and L 2 is the thickness of said second magnetic layer.

Claim 5

A magnetooptical recording medium according to Claim I, wherein said first magnetic layer has a Curie point in a range from 70 to 180°C, and said second magnetic layer has a Curie point in a range from 150 to 400°C.

Claim 6

A magnetooptical recording medium according to Claim I, wherein said first magnetic layer has a coercive force in a range from 3 to 10 KOe, and said second magnetic layer has a coercive force in a range from 0.5 to 2 KOe.

Claim 7

A magnetooptical recording medium according to Claim I, wherein said second magnetic layer has a compensation temperature T Hcomp higher than the Curie point of the first magnetic layer, and the coercive force H Lo of the second magnetic layer at a temperature T L satisfies a condition:

Claim 8

A magnetooptical recording medium according to Claim I, further comprising an adjusting layer between said first and second magnetic layer, for the purpose of adjusting said magnetic wall energy δ w .

Claim 9

A magnetooptical recording medium according to Claim 8, wherein said adjusting layer is composed of a material selected from Ti, Cr, AI, Ni, Fe, Co, rare earth elements and transition metals and has a thickness in a range from 5 to 50 A.

Claim 10

A magnetooptical recording medium according to Claim 8, wherein said adjusting layer is composed of a magnetic material exhibiting surfacial magnetic anisotropy at room temperature and vertical magnetic anisotropy at temperatures close to the Curie point of said first magnetic layer.

Claim 11

II. A magnetooptical recording medium according to Claim 10, wherein said first magnetic layer, second magnetic layer and adjusting layer are composed of alloys of rare earth element and transition metal, in which the first magnetic layer has a composition rich in the transition metal compared with the compensation composition, said second magnetic layer and adjusting layer have compositions both rich in the rare earth element compared with the compensation compositions.

Claim 12

A magnetooptical recording medium according to Claim I, further comprising a protective layer composed of dielectric at least on one side of said first and second magnetic layers.

Claim 13

A magnetooptical recording medium according to Claim 12, wherein said protective layer has a thickness at least equal to 200 A.

Claim 14

A magnetooptical recording medium according to Claim 12, comprising protective layers of a same material, provided on both external faces of said first and second magnetic layers.

Claim 15

An information recording process on a magnetooptical recording medium provided with a first magnetic layer and a second magnetic layer having a higher Curie point and a lower coercive force than those of said first magnetic layer, comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said second magnetic layer but insufficient for inverting the magnetization of said first magnetic layer; and (b) selectively effecting either a first type recording by irradiating said medium with a light beam of a power for heating the medium close to the Curie point of the first magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer while retaining the magnetization of the second magnetic layer, or a second type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point of the second magnetic layer, thereby inverting the magnetization of said second magnetic layer and simultaneously orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer, according to information signal.

Claim 16

A recording process according to Claim 15, which comprises satisfying conditions: wherein H H is the coercive force of the first magnetic layer, and B is the intensity of the first magnetic field.

Claim 17

A recording process according to Claim 16, wherein said first magnetic layer has a coercive force H H more than 5 KOe.

Claim 18

A magnetooptical recording apparatus comprising: means for irradiating a magnetooptical recording medium with a light beam which is intensity modulated between two non-zero values according to the information to be recorded; means of moving said medium relative to said light beam; first magnetic field generating means for applying a bias magnetic field of a predetermined direction to said medium at a position of light beam irradiation; and second magnetic field generating means for applying a bias magnetic field of a direction opposite to said predetermined direction, at a position of the medium different from said position of light beam irradiation.

Claim 19

A magnetooptical recording apparatus according to Claim 18, wherein said light beam irradiation means is an optical head comprising a light source and an optical system for focusing a light beam from said light source onto said medium.

Claim 20

A magnetooptical recording apparatus according to Claim 18, wherein said first and second magnetic field generating means are composed of magnets positioned close to said medium.

Claim 21

A magnetooptical recording medium provided with a first magnetic layer with a Curie point T 1 and a coercive force H 1 , and a second magnetic layer with a Curie point T 2 and a coercive force H 2 and exchangecoupled with said first magnetic layer, which comprises satisfying following conditions: at room temperature wherein M s2 is the saturation magnetization of the second magnetic layer, and Ow is the magnetic wall energy between two magnetic layers; and (B) T 1momp < room temp. < T 2comp < T 1 ≦ T 2 wherein T 1comp is the compensation temperature of the first magnetic layer; and T 2comp is the compensation temperature of the second magnetic layer.

Claim 22

A magnetooptical recording medium according to Claim 21, wherein said second magnetic layer has a compensation temperature T2comp in a range from 50 to 180°C.

Claim 23

A magnetooptical recording medium according to Claim 21, wherein said first and second magnetic layers are composed of materials selected from GdCo, GdFe, TbFe, DyFe, GdTbFe, TbDyFe, GdFeCo, TbFeCo, GdTbCo and GdTbFeCo.

Claim 24

An information recording process on a magnetooptical recording medium provided with a first magnetic layer with a Curie point T 1 and a coercive force H 1 , and a second magnetic layer with a Curie point T 2 and a coercive force H 2 and exchange-coupled with said first magnetic layer, and satisfying conditions: at room temperature wherein M s2 is the saturation magnetization of the second magnetic layer and σ w is the magnetic wall energy between two magnetic layers; and ( B ) T icom p < room temp. < T 2com p < T 1 ≦ T 2 wherein T 1comp is the compensation temperature of the first magnetic layer: and T 2comp is the compensation temperature of the second magnetic layer, comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said second magnetic layer but insufficient for inverting the magnetization of said first magnetic layer; and (b) selectively effecting either a first type recording by irradiating said medium with a light beam of a power for heating the medium close to the compensation temperature T 2comp of the first magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer while retaining the magnetization of the second magnetic layer, or a second type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point T 2 of the second magnetic layer, thereby inverting the magnetization of said second magnetic layer and simultaneously orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer, according to information signal.

Claim 25

An information recording process on a magnetooptical recording medium provided with a first magnetic layer and a second magnetic layer having a compensation temperature higher than the Curie point of said first magnetic layer and a coercive force lower than that of said first magnetic layer and exchange-coupled with said first magnetic layer, comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said second magnetic layer but insufficient for inverting the magnetization of said first magnetic layer; and (b) selectively effecting either a first type recording by irradiating said medium with a light beam of a power for heating the medium close to the Curie point of the first magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer while retaining the magnetization of the second magnetic layer, or a second type recording by irradiating the medium with a light beam of a power for heating the medium beyond the compensation temperature of the second magnetic layer, thereby inverting the magnetization of said second magnetic layer and simultaneously orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetization of the second magnetic layer, according to information signal.

Claim 26

A magnetooptical recording medium provided, in succession on a substrate, with a first magnetic layer with a high Curie point T H1 and a low coercive force H L1 , a second magnetic layer with a lower Curie point T L2 and a higher coercive force H H2 compared with those of said first magnetic layer, and a third magnetic layer with a higher Curie point T H3 and a lower coercive force H L3 compared with those of said second magnetic layer; wherein said three magnetic layers are mutually so coupled as to satisfy conditions: and wherein σ w12 is the magnetic wall energy of the first and second magnetic layers; σ w23 is the magnetic wall energy of the second and third magnetic layers; hi, h 2 and h 3 are respective thicknesses of the first, second and third magnetic layers; and M s1 , M s2 and M s3 are respectively saturation magnetizations of said layers.

Claim 27

A magnetooptical recording medium according to Claim 26, wherein the Curie points and coercive- forces of said first and third magnetic layers satisfy relations: and

Claim 28

A magnetooptical recording medium according to Claim 26, wherein the Curie points of said three magnetic layers are respectively in a range of 150 to 400°C for T H1 , 70 to 200°C for T H2 , and 100 to 250°C for T H3

Claim 29

A magnetooptical recording medium according to Claim 26, wherein the coercive forces of said three magnetic layers are respectively in a range of 0.1 to I KOe for H L1 , 2 to 10 KOe for H H2 , and 0.5 to 4 KOe for H L3 .

Claim 30

A magnetooptical recording medium according to Claim 26, wherein said first, second and third magnetic layers are composed of alloys of rare earth element and transition metal, wherein the first and second magnetic layers have compositions both rich in the rare earth element compared with the compensation composition, while the third magnetic layer has a composition rich in the transition metal compared with the compensation composition.

Claim 31

A magnetooptical recording medium according to Claim 26, wherein said first, second and third magnetic layers are composed of alloys of rare earth element and transition metal, wherein the first and second magnetic layers have compositions both rich in the transition metal compared with the compensation composition, while the third magnetic layer has a composition rich in the rare earth element compared with the compensation composition.

Claim 32

A magnetooptical recording medium according to Claim 26, wherein said first, second and third magnetic layers are composed of alloys selected from GdCo, GdFe, TbFe, DyFe, GdTbFe, TbDyFe, GdFeCo, TbFeCo, GdTbCo and GdTbFeCo.

Claim 33

An information recording process on a magnetooptical recording medium provided, in succession on a substrate, with a first magnetic layer with a high Curie point T H1 and a low coercive force H L1 , a second magnetic layer with a lower Curie point TL2 and a higher coercive force H H2 compared with those said first magnetic layer, and a third magnetic layer with a higher Curie point T H3 and a lower coercive force H L3 compared with those of said second magnetic layer, wherein said three magnetic layers are mutually socoupled as to satisfy conditions: and wherein σ w12 is the magnetic wall energy of the first and second magnetic layers; σ w23 is the magnetic wall energy of the second and third magnetic layers: hi, h 2 and h 3 are respective thicknesses of the first, second and third magnetic layers; and M s1 , M s2 and M s are respectively saturation magnetizations of said layers, comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said third magnetic layer but in capable of inverting the magnetization of said second magnetic layer; and (b) selectively effecting either a first type recording by irradiating said medium with a light beam of a power for heating the medium close to the Curie point T L2 of the second magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting the magnetizations of the first and second magnetic layer in a stable direction with respect to the-magnetization of the third magnetic layer while retaining the magnetization of the third magnetic layer, or a second type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point T H3 of the third magnetic layer, thereby inverting the magnetization of said third magnetic layer and simultaneously orienting the magnetizations of the first and second magnetic layers in a stable direction with respect to the magnetization of the third magnetic layer, according to information signal.

Claim 34

A magnetooptical recording medium provided, in succession on a substrate, with a first magnetic layer with a Curie point T 1 and a coercive force H 1 , a second magnetic layer with a Curie point T 2 and a coercive force H 2 and a third magnetic layer with a Curie point T 3 and a coercive force H 3 , which comprises satisfying conditions: (A) that each magnetic layer is composed principally of an amorphous alloy of rare earth element and transition metal; (B) that H 1 > H 3 > H 2 and (C) that the first magnetic layer has a composition rich in the transition metal compared with the compensation composition and the second and third magnetic layers have compositions both rich in the rare earth element, or that the first magnetic layer has a composition rich in the rare earth element and the second and third magnetic layers have compositions both rich in the transition metal.

Claim 35

A magnetooptical recording medium according to Claim 34, wherein the Curie points of said three magnetic layers are respectively in the ranges of 150 to 400°C for T 3 , 70 to 200°C for T 1 and 90 to 400°C for T 2 .

Claim 36

A magnetooptical recording medium according to Claim 34, wherein the coercive forces of said three magnetic layers are respectively in the ranges of 0.1 to I KOe for H 2 , 2 to 10 KOe for H 1 , and 0.5 to 4 KOe for H 3 .

Claim 37

An information recording process on a magnetooptical recording medium provided, in succession on a substrate, with a first magnetic layer with a Curie point T 1 and a coercive force H 1 , a second magnetic layer with a Curie point T 2 and a coercive force H2 and a third magnetic layer with a Curie point T 3 and a coercive force H 3 , and satisfying conditions: (A) that each magnetic layer is composed principally of an amorphous alloy of rare earth element and transition metal; (B) that H 1 > H 3 > H 2 and T 3 ≧ T 2 > T 1 ; and (C) that the first magnetic layer has a composition rich in the transition metal compared with the compensation composition while the second and third magnetic layers have compositions both rich in the rare earth element, or that the first magnetic layer has a composition rich in the rare earth element while the second and third magnetic layers have compositions both rich in the transition metal, comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said second and third magnetic layers but incapable of inverting the magnetization of said first magnetic layer; and (b) selectively effecting either a first type recording by irradiating said medium with a light beam of a power for heating the medium close to the Curie point T 1 of said first magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetizations of the second and third magnetic layer while retaining the magnetizations of the second and third magnetic layers, or a second type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point T 3 of the third magnetic layer thereby inverting the magnetization of said second and third magnetic layers and simultaneously orienting the magnetization of the first magnetic layer in a stable direction with respect to the magnetizations of the second and third magnetic layers, according to information signal.

Claim 38

A magnetooptical recording medium provided, on at least a substrate, with a quadraple-layered magnetic film consisting of a first magnetic layer with a Curie point T 1 , a coercive force H 1 , a thickness h 1 and a saturation magnetization M s1 , a second magnetic layer with a Curie point T 2 , a coercive force H 2 , a thickness h 2 and a saturation magnetization M s2 , a third magnetic layer with a Curie point T 3 , a coercive force H 3 , a thickness h 3 and a saturation magnetization M s3 , and a fourth magnetic layer with a Curie point T 4 , a coercive force H 4 , a thickness h 4 and a saturation magnetization M s4 , in which said magnetic layers are exchange-coupled, wherein said four magnetic layers are so coupled as to satisfy conditions: (I) as for the Curie points of the maqnetic lavers: (II) as for the coercive forces of the magnetic layers: (III) as for the thicknesses of the magnetic layers: and ( IV ) as for the saturation magnetizations, thicknesses, coercive forces and magnetic wall energies of the magnetic layers: wherein σ w12 , σσ w23 and δ w34 are magnetic wall energies respectively for the first and second magnetic layers, second and third magnetic layers, and third and fourth magnetic layers.

Claim 39

An information recording process on a magnetooptical recording medium provided, at least on a substrate, with a quadraple-layered magnetic film consisting of a first magnetic layer with a Curie point Ti, a coercive force Hi, a thickness hi and a saturation magnetization M s1 , a second magnetic layer with a Curie point T 2 , a coercive force H 2 , a thickness h 2 and a saturation magnetization M s2 , a third magnetic layer with a Curie point T s , a coercive force H 3 , a thickness h 3 and a saturation magnetization M s3 , and a fourth magnetic layer with a Curie point T 4 , a coercive force H 4 , a thickness h 4 and a saturation magnetization M s4 , in which said magnetic layer are so exchange-coupled as to satisfy following conditions: (I) as for the Curie points of the magnetic layers: (II) as for the coercive forces of the magnetic layers: (III) as for the thicknesses of the magnetic layers: and (IV) as for the saturation magnetizations, thicknesses, coercive forces and magnetic wall energies of the magnetic layers: wherein σ w12 , σ w23 and σ w34 are magnetic wall energies respectively for the first and second magnetic layers, second and third magnetic layers, and third and fourth magnetic layers comprising steps of: (a) applying a first magnetic field of a magnitude enough for uniformly magnetizing said fourth magnetic layer but incapable of inverting the magnetization of the second magnetic layer; and (b) selectively effecting either a first type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point T 2 of the second magnetic layer while applying a bias field opposite in direction to said first magnetic field, thereby orienting, across the third magnetic layer, the magnetizations of the first and second magnetic layer in a stable direction with respect to the magnetization of the fourth magnetic layer while retaining the magnetization of the fourth magnetic layer, or a second type recording by irradiating the medium with a light beam of a power for heating the medium close to the Curie point T 4 of the fourth magnetic layer thereby inverting the magnetization of said fourth magnetic layer and simultaneously orienting the magnetizations of the first, second and third magnetic layers in a stable direction with respect to the magnetization of said fourth magnetic layer, according to information signal.