Magneto-optical recording media and apparatus

A magneto-optical recording system for recording information with bits having upward magnetization and having downward magnetization on a recording layer of a magneto-optical recording medium, comprising:

• a magneto-optical recording medium having a first magnetic layer with perpendicular magnetic anisotropy, said first magnetic layer having a Curie temperature Tc1, a second magnetic layer disposed on this first magnetic layer and coupled to said first magnetic layer by an exchange force, said second magnetic layer having a Curie temperature Tc2, a third magnetic layer disposed on this second magnetic layer and coupled to said second magnetic layer by an exchange force, said third magnetic layer having a Curie temperature Tc3, and a fourth magnetic layer disposed on this third magnetic layer and coupled to said third magnetic layer by an exchange force, said fourth magnetic layer having a Curie temperature Tc4;
• a laser for emitting a laser beam;
• a means for directing the laser beam onto the medium;
• and a means for modulating said beam to heat said magneto-optical recording medium to at least two values according to binary information to be recorded;
• said magneto-optical recording medium satisfying:
• Tc4>Tc1,
• Tc4>Tc3,
• Tc2>Tc1, and
• Tc2>Tc3,
• a magnetization of the first magnetic layer being not reversed by magnetic reversal of the second magnetic layer at room temperature,
• wherein
• a sublattice magnetization direction of each of the second magnetic layer, the third magnetic layer, and the fourth magnetic layer is initialized so as to be aligned in one of two opposite directions at room temperature after recording, and
• under illumination by the laser beam that heats said magneto-optical medium to the higher temperature of said two laser beam values, a magnetization value of the fourth magnetic layer is reduced as compared to a magnetization value of the fourth magnetic layer in the vicinity of room temperature, whereby a stray magnetic field generated by said magneto-optical recording medium acts so that the sublattice magnetization direction of the second magnetic layer is recorded in the direction opposite to said initialization direction.

A magneto-optical recording medium for use in a system for recording information as regions having a first magnetization direction and other regions having a second magnetization direction, comprising:

• a first magnetic layer having vertical magnetic anisotropy, having a magnetization and having a Curie temperature Tc1;
• a second magnetic layer disposed on the first magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc2, and having a magnetization with a direction which is more easily reversed than the magnetization of the first magnetic layer;
• a third magnetic layer disposed on the second magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc3;
• and
• a fourth magnetic layer disposed on the third magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc4, and having a magnetization with a direction that does not change while recording information and which has a first value at room temperature and which has a second value less than the first value at a predetermined temperature elevated above room temperature, whereby a magnetic field near a region of the fourth magnetic layer heated to the predetermined, temperature acts to magnetize the second magnetic layer in a direction opposite the constant direction;
• said Curie temperatures satisfying:
• Tc4>Tc1,
• Tc4>Tc3,
• Tc2>Tc1, and
• Tc2>Tc3.

A magneto-optical recording medium for use in a system for recording information as regions having a first magnetization direction and other regions having a second magnetization direction, comprising:

• a first magnetic layer having vertical magnetic anisotropy, having a magnetization and having a Curie temperature Tc1;
• a second magnetic layer disposed on the first magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc2, and having a magnetization with a direction which is more easily reversed than the magnetization of the first magnetic layer;
• a third magnetic layer disposed on the second magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc3;
• and
• a fourth magnetic layer disposed on the third magnetic layer and coupled thereto by an exchange force, having vertical magnetic anisotropy, having a Curie temperature Tc4;
• said Curie temperatures satisfying:
• Tc4>Tc1,
• Tc4>Tc3,
• Tc2>Tc1, and
• Tc2>Tc3;
• and
• wherein the fourth magnetic layer has a magnetization at a predetermined temperature greater than room temperature that is less than the magnetization at room temperature, and the magnetization has a direction at the predetermined temperature which is the same as the direction at room temperature.

A magneto-optical recording medium for use in a system for recording information as region have a first magnetization direction and other regions having a second magnetization direction, comprising:

• a first magnetic layer have a Curie temperature Tc1;
• a second magnetic layer disposed on the first magnetic layer having a Curie temperature Tc2;
• a third magnetic layer disposed on the second magnetic layer having a Curie temperature Tc3;
• and a fourth magnetic layer disposed on the third magnetic layer having a Curie temperature Tc4;
• said magnetic layers having vertical magnetic anisotropy, and adjacent magnetic layers coupled each to the other by an exchange force;
• said Curie temperatures satisfying:
• Tc4>Tc1,
• Tc4>Tc3,
• Tc2>Tc1, and
• Tc2>Tc3;
• wherein the fourth magnetic layer has a magnetization at predetermined temperature greater than room temperature that is less than the magnetization at room temperature, and the magnetization has a direction at the predetermining temperature which is the same as the direction at room temperature, whereby a field magnetostatically coupled from the fourth layer to the second layer at the predetermined temperature has a field direction that is opposite to the field direction at room temperature;
• and
• wherein the magnetization of the second magnetic layer has a direction which is more easily reversed than the magnetization of the first magnetic layer, and further wherein the magnetization direction of the second magnetic layer is easily oriented by the field magnetostatically coupled from the fourth magnetic layer.