Magneto-optical recording medium whereon recording is carried out with an overwriting function

A magneto-optical recording medium provided with a substrate through which a light beam is to be transmitted and a recording-reproduction layer whereon information is recorded,

• said recording-reproduction layer comprising:
• a recording layer made of rare earth-transition metal alloys having a Curie temperature, easy magnetization axis thereof exhibiting a magnetization perpendicular to said recording layer within a range between a first temperature and the Curie temperature, and the easy magnetization axis thereof exhibiting a magnetization parallel to said recording layer at temperature below the first temperature while keeping components of a perpendicular magnetization, the first temperature being set within a range between room temperature and the Curie temperature;
• and
• writing layer made of rare earth-transition metal alloys having a Curie temperature above the Curie temperature of said recording layer and such coercive force that a magnetization direction thereof is switched by an external magnetic field at room temperature,
• said recording layer and said writing layer being laminated in this order on the substrate,
• wherein as the temperature of said recording-reproduction layer is raised within a range between the Curie temperature of said recording layer and the Curie temperature of said writing layer by irradiating thereon with a light beam, the magnetization direction of said recording layer is arranged in a magnetization direction of said writing layer, and as the temperature of said recording-reproduction layer is raised above the Curie temperature of said writing layer, a magnetization direction of said recording layer is arranged in the magnetization direction of an external recording magnetic field.

A system for recording and reproducing information, comprising:

• a magneto-optical recording medium provided with a substrate through which a light beam is to be transmitted and a recording-reproduction layer whereon information is recorded magneto-optically;
• and
• a recording and reproduction device;
• said recording and reproduction device including:
• means for projecting light beams having a plurality of light intensities on said magneto-optical recording medium;
• means for applying initialization-use magnetic field to the magneto-optical recording medium;
• and
• means for applying recording magnetic field to the magneto-optical recording medium;
• said recording and reproduction layer including:
• a recording layer for storing information, said recording layer being made of rare earth-transition metal alloys having Curie temperature;
• a readout layer made of rare earth-transition metal alloys having Curie temperature below the Curie temperature of said recording layer, an easy magnetization axis of said readout layer exhibiting a magnetization perpendicular to said recording layer within a range between a first temperature and a second temperature, and the easy magnetization axis of said readout layer exhibiting a magnetization parallel to said recording layer when the temperature is below the first temperature, the first temperature being set below the second temperature and both the first and the second temperatures being set within the range between room temperature and the Curie temperature of said readout layer;
• and
• writing layer made of rare earth-transition metal alloys having Curie temperature that is above the Curie temperature of said recording layer and such coercive force that a magnetization direction thereof is switched by an external magnetic field at room temperature,
• said readout layer, said recording layer and said writing layer being laminated in this order,
• wherein as the temperature of said recording-reproduction layer is raised to a temperature within the range between the Curie temperature of said recording layer and the Curie temperature of said writing layer by irradiating thereon with a light beam, the magnetization direction of said recording layer is arranged in a magnetization direction of said writing layer, and as the temperature of said recording-reproduction layer is raised above the Curie temperature of said writing layer, a magnetization direction of said recording layer is arranged in the magnetization direction of an external recording magnetic field.

A method for recording using an overwriting function on a magneto-optical recording medium comprising a recording-reproduction layer including a recording layer and a writing layer made of rare earth-transition metal alloys whose Curie temperature is above Curie temperature of said recording layer, comprising the steps of:

• arranging a magnetization direction of the writing layer in a magnetization direction of an initialization-use magnetic field by initialization-use magnetic field generation means;
• projecting a light beam on the magneto-optical recording medium;
• raising a temperature of said recording-reproduction layer to a temperature within a range between the Curie temperature of said recording layer and the Curie temperature of said writing layer by irradiation thereon with the light beam;
• making the magnetization direction of said recording layer coincident with the magnetization direction of said writing layer;
• raising the temperature of said recording-reproduction layer above the Curie temperature of said writing layer by irradiating thereon with the light beam;
• and
• making respective magnetization directions of said writing layer and said recording layer opposite to the magnetization direction of the initialization-use magnetic field by an external recording magnetic field.