Optomagnetic recording, reading and erasing method and implementing apparatus which permits overwriting of previously recorded information

Claim 1

An optomagnetic recording and reading apparatus comprising: an optical head for applying a laser beam onto a recording medium for heating the recording medium and for receiving the laser beam after passing through or reflecting from the recording medium in reading information; a servo control unit responsive to the transmitted or reflected laser beam received by said optical head for reducing focussing and/or tracking errors; and means for applying an external magnetic field to the recording medium, said applying means comprising a pair of permanent magnet assemblies disposed respectively at the opposite sides of the recording medium, each of said permanent magnet assemblies having a permanent magnet and a magnetic core equipped with a wire winding, and an electric current source supplying electric current to the wire windings of the permanent magnet assemblies.

Claim 19

An apparatus for recording and reading a perpendicularly magnetizable magneto-optical recording medium, including an optical head applying a laser beam onto the recording medium and receiving the laser beam after it has passed through or been reflected from the recording medium, and means for applying an external magnetic field to the recording medium in the neighborhood of a domain where the laser beam is impinged onto the recording medium, characterized in that, said means for applying an external magnetic field comprises a first permanent magnet assembly and a second permanent magnet assembly each consisting of a permanent magnet and a core of high permeability material having a winding thereabout and disposed respectively at the opposite sides of the recording medium, and, said windings being connected to such an electric current source that energizes said windings of the first and second permanent magnet assemblies alternately so that the first permanent magnet assembly creates a magnetic field having a predetermined intensity of magnetic flux and passing through the recording medium in a first direction and the second permanent magnet assembly creates a magnetic field having a predetermined intensity of magnetic flux and passing through the recording medium in a second direction which is opposite to the first direction.

Claim 20

An apparatus for recording and reading a perpendicularly magnetizable magneto-optical recording medium, including an optical head applying a laser beam onto the recording medium and receiving the laser beam after it has passed through or been reflected from the recording medium, and means for applying an external magnetic field to the recording medium in the neighborhood of a domain where the laser beam is impinged onto the recording medium, characterized in that, said means for applying an external magnetic field comprises a first permanent magnet assembly and a second permanent magnet assembly each consisting of a permanent magnet and a core of high permeability material having a winding thereabout and disposed respectively at the opposite sides of the recording medium, and, said windings being connected to such an electric current source that energizes said windings of the first and second permanent magnet assemblies alternately so that the first permanent magnet assembly creates a magnetic field having a predetermined intensity of magnetic flux and passing through the recording medium in a first direction and the second permanent magnet assembly creates a magnetic field having a predetermined intensity of magnetic flux and passing through the recording medium in a second direction which is opposite to the first direction.