Magneto-optical recording medium, recording and playback method and apparatus for the same

A recording and playback apparatus for a magneto-optical recording medium including a transparent substrate, and a transparent interference layer, a first magneto-optical layer having a first Curie temperature, a second magneto-optical layer containing a perpendicularly magnetizable amorphous alloy as a main component thereof having a second Curie temperature lower than the first Curie temperature, a third magneto-optical layer containing a perpendicularly magnetizable amorphous alloy as a main component thereof having a third Curie Temperature lower than the first Curie temperature and higher than the second Curie temperature, and a dielectric protective layer which are laminated in this order on said substrate, said first magneto-optical layer, second magneto-optical layer and third magneto-optical layer being exchanged-coupled at a temperature ranging from approximately 10.degree. C. to approximately 90.degree. C., said transparent substrate having a plurality of test regions each for providing a test signal, said apparatus comprising:

• a first laser source for irradiating a main laser beam through said transparent substrate to a first track of said first magneto-optical layer while moving said main laser beam relative to said magneto-optical recording medium, the main laser beam having an amount of energy for substantially diminishing magnetization of said second magneto-optical layer in a first portion of a main beam area irradiated by said main laser beam and leaving magnetization of said second magneto-optical layer unchanged in a second portion of said main beam area;
• a second laser source for irradiating at least one sub-main laser beam through said transparent substrate to a second track of said first magneto-optical layer adjacent to the first track while moving said sub-main laser beam relative to said magneto-optical recording medium in the direction of said relative movement of said main laser beam, said sub-main laser beam having an amount of energy for substantially diminishing magnetization of said second magneto-optical layer at least in a portion of a sub-main beam area irradiated by said sub-main laser beam, said sub-main beam area being adjacent to said second portion in the direction perpendicular to said relative movement;
• magnetic field providing means for applying a bias magnetic field to a space including said first magneto-optical layer simultaneously with said irradiating of said main laser beam, thereby deforming magnetization of said first magneto-optical layer in said first portion of said main beam area;
• test signal evaluating means for reading said test signals and calculating a bit error rate by comparing said test signals with a predetermined signal corresponding to said test signals;
• and
• power adjusting means for adjusting at least one of the energies of said main and sub-main laser beams and deciding an optimum energy of said laser beams generating a minimum bit error rate.

A recording and playback apparatus for a magneto-optical recording medium including a transparent substrate, and a transparent interference layer, a first magneto-optical layer having a first Curie temperature, a second magneto-optical layer containing a perpendicularly magnetizable amorphous alloy as a main component thereof having a second Curie temperature lower than the first Curie temperature, a third magneto-optical layer containing a perpendicularly magnetizable amorphous alloy as a main component thereof having a third Curie Temperature lower than the first Curie temperature and higher than the second Curie temperature, and a dielectric protective layer which are laminated in this order on said substrate, the first magneto-optical layer, second magneto-optical layer and third magneto-optical layer being exchanged-coupled at a temperature ranging from approximately 10.degree. C. to approximately 90.degree. C., said apparatus comprising

• a first laser source for irradiating a first laser beam for reading use through said transparent substrate to said first magneto-optical layer, the power of said first laser beam being enough for substantially diminishing magnetization of said second magneto-optical layer in a portion of laser beam area irradiated by said first laser beam;
• first magnetic field providing means comprising a permanent magnet for applying a bias magnetic field for reading use to a space including said first magneto-optical layer simultaneously with said irradiating of said first laser beam, thereby deforming the magnetization of said first magneto-optical layer in said portion of said laser beam area;
• a second laser source, separately from said first laser source, for irradiating a laser beam for writing use;
• and
• second magnetic field providing means comprising an electromagnet, separately from said first magnetic field providing means, for applying a writing bias magnetic field for writing use.