Magneto-optical recording medium

Claim 1

A magneto-optical recording medium which has, on a transparent substrate (1), a magneto-optical recording layer consisting of a first magnetic film (11), a second magnetic film (12) and a third magnetic film (13) which are magnetically coupled to one another at room temperature, T RT , wherein the Curie point, T c1 , T c2 and T c3 of the first, second and third magnetic films, respectively, have the relationships of 60°C ≦ T c2 ≦ 200°C, T c2 < T c1 and T c2 < T c3 , and the coercive force, H c1 , of the first magnetic film is so selected as to be small in the vicinity of the Curie point, T c2 , of the second magnetic film and the coercive force, H c3 , of the third magnetic film is so selected as to be larger than a required minimum magnetic field intensity within a temperature range between said room temperature T RT , and a predetermined temperature, T PB , which is higher than the Curie point, T c2 , of the second magnetic film, wherein the first magnetic film is mainly composed of GdFeCo and the saturation magnetization, M s1 , of the first magnetic film is not greater than 200 emu/cc when the sublattice of the transition metals is more predominant than that of the rare earth element or when the sublattice of the rare earth element is more predominant than the sublattice of the transition metals, and wherein the third magnetic film is mainly composed of TbFeCo and the saturation magnetization, M s3 , of the third magnetic film is not greater than 300 emu/cc when the sublattice of the transition metals is more predominant than the sublattice of the rare earth element or not greater than 160 emu/cc when the sublattice of the rare earth element is more predominant than sublattice of the transition metals.

Claim 3

A method for reproducing a signal of a recorded magnetic domain from a magneto-optical recording medium having a first magnetic film, a second magnetic film and a third magnetic film which are magnetically coupled to one another at room temperature, T RT , wherein the Curie points, T c1 , T c2 and T c3 of the first, second and third magnetic films, respectively, have the relationships of T c2 > T RT , T c2 < T c1 and T c2 < T c3 , and the coercive force, H c1 , of the first magnetic film is so selected as to be small in the vicinity of the Curie point, T c2 , of the second magnetic film and the coercive force, H c3 , of the third magnetic film is so selected as to be larger than a required minimum magnetic field intensity within a temperature range between said room temperature T RT , and a predetermined temperature, T PB , which is higher than the Curie point, T c2 , of the second magnetic film, wherein the first magnetic film is mainly composed of GdFeCo and the saturation magnetization, M s1 , of the first magnetic film is not greater than 200 emu/cc when the sublattice of the transition metals is more predominant than that of the rare earth element or when the sublattice of the rare earth element is more predominant than the sublattice of the transition metals, and wherein the third magnetic film is mainly composed of TbFeCo and the saturation magnetization, M s3 , of the third magnetic film is not greater than 300 emu/cc when the sublattice of the transition metals is more predominant than the sublattice of the rare earth element or not greater than 160 emu/cc when the sublattice of the rare earth element is more predominant than sublattice of the transition metals, which method comprising, upon the reproduction of the signal from the magneto-optical recording medium, heating the medium to the predetermined temperature, T PB , to interrupt the magnetic coupling between the first and third magnetic films with application of a magnetic field for demagnetizing magnetic fields or stray magnetic fields from the recording medium and an external magnetic field sufficient to provide the required magnetic intensity to change a domain size in the first magnetic film.

Claim 4

A method for reproducing a signal of a recorded magnetic domain from a magneto-optical recording medium having a first magnetic film, a second magnetic film and a third magnetic film which are magnetically coupled to one another at room temperature, T RT , wherein the Curie points, T c1 , T c2 and T c3 of the first, second and third magnetic films, respectively, have the relationships of T c2 > T RT , T c2 < T c1 and T c2 < T c3 , and the coercive force, H c1 , of the first magnetic film is so selected as to be small in the vicinity of the Curie point, T c2 , of the second magnetic film and the coercive force, H c3 , of the third magnetic film is so selected as to be larger than a required minimum magnetic field intensity within a temperature range between said room temperature T RT , and a predetermined temperature, T PB , which is higher than the Curie point, T c2 , of the second magnetic film, wherein the first magnetic film is mainly composed of GdFeCo and the saturation magnetization, M s1 , of the first magnetic film is not greater than 200 emu/cc when the sublattice of the transition metals is more predominant than that of the rare earth element or when the sublattice of the rare earth element is more predominant than the sublattice of the transition metals, and wherein the third magnetic film is mainly composed of TbFeCo and the saturation magnetization, M s3 , of the third magnetic film is not greater than 300 emu/cc when the sublattice of the transition metals is more predominant than the sublattice of the rare earth element or not greater than 160 emu/cc when the sublattice of the rare earth element is more predominant than sublattice of the transition metals, which method comprising, upon the reproduction of the signal from the magneto-optical recording medium, heating the medium to the predetermined temperature, T PB , to interrupt the magnetic coupling between the first and third magnetic films with application of a magnetic field for demagnetizing magnetic fields or stray magnetic fields from the recording medium and an external magnetic field sufficient to provide the required magnetic intensity to the first magnetic film to cause shrinking of the recorded magnetic domain.

Claim 5

A method for reproducing a signal of a recorded magnetic domain from a magneto-optical recording medium having a first magnetic film, a second magnetic film and a third magnetic film which are magnetically coupled to one another at room temperature, T RT , wherein the Curie points, T c1 , T c2 and T c3 of the first, second and third magnetic films, respectively, have the relationships of T c2 > T RT , T c2 < T c1 and T c2 < T c3 , and the coercive force, H c1 , of the first magnetic film is so selected as to be small in the vicinity of the Curie point, T c2 , of the second magnetic film and the coercive force, H c3 , of the third magnetic film is so selected as to be larger than a required minimum magnetic field intensity within a temperature range between said room temperature T RT , and a predetermined temperature, T PB , which is higher than the Curie point, T c2 , of the second magnetic film, wherein the first magnetic film is mainly composed of GdFeCo and the saturation magnetization, M s1 , of the first magnetic film is not greater than 200 emu/cc when the sublattice of the transition metals is more predominant than that of the rare earth element or when the sublattice of the rare earth element is more predominant than the sublattice of the transition metals, and wherein the third magnetic film is mainly composed of TbFeCo and the saturation magnetization, M s3 , of the third magnetic film is not greater than 300 emu/cc when the sublattice of the transition metals is more predominant than the sublattice of the rare earth element or not greater than 160 emu/cc when the sublattice of the rare earth element is more predominant than sublattice of the transition metals, which method comprising, upon the reproduction of the signal from the magneto-optical recording medium, heating the medium to the predetermined temperature, T PB , to interrupt the magnetic coupling between the first and third magnetic films with application of a magnetic field for demagnetizing magnetic fields or stray magnetic fields from the recording medium and an external magnetic field sufficient to provide the required magnetic intensity to the first magnetic film to expand the recorded magnetic domain.

Claim 6

A method according to any of Claims 3, 4 and 5, wherein the signal is obtained by detecting signal change upon change of the domain size.

Claim 7

A method for reproducing information signals from a magneto-optical recording medium having a first magnetic film, a second magnetic film and a third magnetic film magnetically coupled to each other at room temperature, T RT , wherein the Curie points, T c1 , T c2 and T c3 of the first, second and third magnetic films, respectively, have the relationships of 60°C ≦ T c2 ≦ 200°C, T c2 < T c1 and T c2 < T c3 , wherein the first magnetic film is mainly composed of GdFeCo and the saturation magnetization, M s1 , of the first magnetic film is not greater than 200 emu/cc when the sublattice of the transition metals is more predominant than that of the rare earth element or when the sublattice of the rare earth element is more predominant than the sublattice of the transition metals, and wherein the third magnetic film is mainly composed of TbFeCo and the saturation magnetization, M s3 , of the third magnetic film is not greater than 300 emu/cc when the sublattice of the transition metals is more predominant than the sublattice of the rare earth element or not greater than 180 emu/cc when the sublattice of the rare earth element is more predominant than sublattice of the transition metals, which method comprising irradiating the medium with a laser beam to cause a first portion where magnetic coupling of the first, second and third magnetic films are extinguished and a second portion where the magnetic coupling of the first, second and third magnetic films is maintained as it is to be formed within a laser beam spot, and reading out the signals from the second portion of the first magnetic film.