Magneto-optical recording medium capable of super resolution reproduction and information reproduction method using the same

Claim 2

A magneto-optical recording medium comprising: a first magnetic layer which becomes an in-plane magnetization film at room temperature, and a perpendicular magnetization film at a temperature between room temperature and the Curie temperature of said layer; a second magnetic layer which has a Curie temperature lower than the Curie temperature of said first magnetic layer, remains a perpendicular magnetization film from room temperature to the Curie temperature thereof, and is stacked on said first magnetic layer; and a third magnetic layer which is arranged between said first and second magnetic layers and has a Curie temperature lower than the Curie temperatures of said first and second magnetic layers, wherein said first magnetic layer is magnetostatically coupled with said second magnetic layer in a region where the temperature of said third magnetic layer has reached a temperature not less than the Curie temperature thereof.

Claim 3

A medium according to claim 1, wherein said first, second, and third magnetic layers consist of rare earth-transition metal element amorphous alloys.

Claim 4

A medium according to claim 1, wherein said first magnetic layer has a compensation temperature between room temperature and the Curie temperature.

Claim 5

A medium according to claim 3, wherein the compensation temperature is set to be not less than the Curie temperature of said second magnetic layer.

Claim 6

A medium according to claim 4, wherein the compensation temperature is higher than the Curie temperature of said second magnetic layer by not less than 20° C.

Claim 7

A medium according to claim 1, wherein the region satisfies Hst+Hleak>Hwb for Hwb=σwb/2Ms1·r where σwb is a Bloch magnetic wall energy, r is a radius of a magnetic domain, Ms1 is the saturation magnetization of said first magnetic layer, Hwb is the magnetic field generated by the Bloch magnetic wall energy, Hleak is the leakage magnetic field, and Hst is the static magnetic field.

Claim 8

A medium according to claim 3, wherein magnetization of said first magnetic layer is oriented in one direction in a region where the following condition is satisfied, Hst+Hleak+Hwb>Hcl for Hwb=σwb/2Ms1·r σwb is a Bloch magnetic wall energy, r is a radius of a magnetic domain, Ms1 is the saturation magnetization of said first magnetic layer, Hwb is the magnetic field generated by the Bloch magnetic wall energy Hleak is the leakage magnetic field of said first magnetic layer, Hst is the static magnetic field applied form said second magnetic layer to said first magnetic layer, and Hc1 is the coercive force of said first magnetic layer.

Claim 9

An information reproduction method of reproducing information from a magneto-optical recording medium including: a first magnetic layer which becomes an in-plane magnetization film at room temperature, and a perpendicular magnetization film at a temperature between room temperature and the Curie temperature of the layer, a second magnetic layer which has a Curie temperature lower than the Curie temperature of the first magnetic layer, remains a perpendicular magnetization film from room temperature to the Curie temperature thereof, and is stacked on the first magnetic layer, and a third magnetic layer which is arranged between the first and second magnetic layers and has a Curie temperature lower than the Curie temperature of the first and second magnetic layer, the first magnetic layer being magnetostatically coupled with the second magnetic layer in a region where the temperature of the third magnetic layer has become not less than the Curie temperature thereof, said method comprising: the step of irradiating the medium with a beam spot; the step of raising the temperature of only a region of the third magnetic layer, which corresponds to portion of the beam spot, to a temperature not less than the Curie temperature thereof to magnetostatically couple the first and second magnetic layers with each other, and transferring information stored in the second magnetic layer to the first magnetic layer; and the step of reproducing the transferred information on the basis of light reflected by the medium.

Claim 10

An information reproduction method of reproducing information from a magneto-optical recording medium including: a first magnetic layer which becomes an in-plane magnetization film at room temperature, and a perpendicular magnetization film at a temperature between room temperature and the Curie temperature of the layer, a second magnetic layer which has a Curie temperature lower than the Curie temperature of the first magnetic layer, remains a perpendicular magnetization film from room temperature to the Curie temperature thereof, and is stacked on the first magnetic layer, and a third magnetic layer which is arranged between the first and second magnetic layers and has a Curie temperature lower than the Curie temperature of the first and second magnetic layer, the first magnetic layer being magnetostatically coupled with the second magnetic layer in a region where the temperature of the third magnetic layer has become not less than the Curie temperature thereof, said method comprising: the step of irradiating the medium with a beam spot; the step of raising the temperature of only a region of the third magnetic layer, which corresponds to portion of the beam spot, to a temperature not less than the Curie temperature thereof to magnetostatically couple the first and second magnetic layers with each other, and transferring information stored in the second magnetic layer to the first magnetic layer; and the step of reproducing the transferred information on the basis of light reflected by the medium.

Claim 11

An information reproduction method of reproducing information from a magneto-optical recording medium including: a first magnetic layer which becomes an in-plane magnetization film at room temperature, and a perpendicular magnetization film at a temperature between room temperature and the Curie temperature of the layer, the first magnetic layer having compensation temperature between room temperature and the Curie temperature, a second magnetic layer which has a Curie temperature lower than the Curie temperature of the first magnetic layer, remains a perpendicular magnetization film from room temperature to the Curie temperature thereof, and is stacked on the first magnetic layer, and a third magnetic layer which is arranged between the first and second magnetic layers and has a Curie temperature lower than the Curie temperatures of the first and second magnetic layers, the first magnetic layer being magnetostatically coupled with the second magnetic layer in a region where the temperature of the third magnetic layer has become not less than the Curie temperature thereof, said method comprising: the step of irradiating the medium with a beam spot; and the step of keeping the in-plane magnetization of the first magnetic layer in a first region in the beam spot, raising the temperature of the third magnetic layer in a second region in the beam spot to a temperature not less than the Curie temperature thereof to magnetostatically couple the first and second magnetic layers with each other, transferring information stored in the second magnetic layer to the first magnetic layer, and raising the temperature of the first magnetic layer to a temperature not less than the compensation temperature thereof in a third region in the beam spot to orient the magnetization of the first magnetic layer in a predetermined direction; and the step of reproducing the transferred information on the basis of light reflected by the medium, wherein the second region is sandwiched between the first and third regions in a traveling direction of the beam spot.

Claim 12

An information reproduction method of reproducing information from a magneto-optical recording medium including: a first magnetic layer which becomes an in-plane magnetization film at room temperature, and a perpendicular magnetization film at a temperature between room temperature and the Curie temperature of the layer, the first magnetic layer having compensation temperature between room temperature and the Curie temperature, a second magnetic layer which has a Curie temperature lower than the Curie temperature of the first magnetic layer, remains a perpendicular magnetization film from room temperature to the Curie temperature thereof, and is stacked on the first magnetic layer, and a third magnetic layer which is arranged between the first and second magnetic layers and has a Curie temperature lower than the Curie temperatures of the first and second magnetic layers, the first magnetic layer being magnetostatically coupled with the second magnetic layer in a region where the temperature of the third magnetic layer has become not less than the Curie temperature thereof, said method comprising: the step of irradiating the medium with a beam spot; and the step of keeping the in-plane magnetization of the first magnetic layer in a first region in the beam spot, raising the temperature of the third magnetic layer in a second region in the beam spot to a temperature not less than the Curie temperature thereof to magnetostatically couple the first and second magnetic layers with each other, transferring information stored in the second magnetic layer to the first magnetic layer, and raising the temperature of the first magnetic layer to a temperature not less than the compensation temperature thereof in a third region in the beam spot to orient the magnetization of the first magnetic layer in a predetermined direction; and the step of reproducing the transferred information on the basis of light reflected by the medium, wherein the second region is sandwiched between the first and third regions in a traveling direction of the beam spot.