Magneto-optical memory medium and apparatus for writing and reading information on and from the medium

Claim 2

A magneto-optical memory medium, consisting of a laminar structure comprising: a plurality of magneto-optical storage layers formed of a magneto-optical material; and at least one non-magnetic layer each of which is interposed between adjacent two layers of said plurality of storage layers, information being written on and read from selected one of said plurality of magneto-optical storage layers.

Claim 3

A magneto-optical memory medium according to claim 1, wherein said laminar structure comprises: a reflector layer reflecting a light beam; a non-magnetic layer formed on said reflector layer; a second magneto-optical layer formed on said non-magnetic layer; another non-magnetic layer formed on said second magneto-optical layer; and a first magneto-optical layer formed on said another non-magnetic layer, information being stored on said first and second magneto-optical storage layers through magnetization thereof in one of opposite directions normal to their surfaces, the information stored on said first and second storage layers being read out through detection of changes in the Kerr rotation angles of a first and a second beam of light of different wavelengths applied to the medium, respectively, said Kerr rotation angles of said first and second beams of light being changed depending upon the direction of magnetization of said first and second storage layers, said first magneto-optical storage layer having a thickness determined so that the change in the Kerr rotation angle of said first beam of light represents the direction of magnetization of said first storage layer, irrespective of the direction of magnetization of said second storage layer, while the change in the Kerr rotation angle of said second beam of light represents the direction of magnetization of said second storage layer, irrespective of the direction of magnetization of said first storage layer.

Claim 4

A magneto-optical memory medium according to claim 1, wherein each of said plurality of magneto-optical storage layers consists of a first magneto-optical film having a comparatively low Curie point, and a second magneto-optical film formed in contact with said first magneto-optical layer, said second magneto-optical film having a comparatively high magneto-optical effect.

Claim 5

A magneto-optical memory medium according to claim 1, wherein said plurality of magneto-optical storage layers have different Curie points.

Claim 6

A magneto-optical apparatus for recording information on a magneto-optical memory medium, comprising: a laser device for emitting a laser beam and directing the laser beam toward said memory medium, for writing information on selected one of a plurality of magneto-optical storage layers which are separated from each other by at least one non-magnetic layer; and means for converging said laser beam selectively on said selected one of the storage layers of the memory medium.

Claim 7

A magneto-optical apparatus for recording information on a magneto-optical memory medium, comprising: a laser device for emitting a laser beam and directing the laser beam toward said memory medium, for writing information on selected one of a plurality of magneto-optical storage layers which are separated from each other by at least one non-magnetic layer; and means for converging said laser beam selectively on said selected one of the storage layers of the memory medium.

Claim 8

A magneto-optical apparatus according to claim 5, wherein said converging means comprises an object lens which has a depth of focus which is smaller than a thickness of each of said at least one non-magnetic layer.

Claim 9

A magneto-optical apparatus for recording information on a magneto-optical memory medium, comprising: at least one light source for emitting a laser beam toward said memory medium, for writing information on selected one of a plurality of magneto-optical storage layers which are separated from each other by at least one non-magnetic layer; an optical device including an object lens positioned opposite to said memory medium, for convering said laser beam; selector means for selecting a focal point of said laser beam on said selected one of the storage layers of the memory medium; and magnetic-field generating means for generating a magnetic field to magnetize a part of said selected one of the storage layers at which said laser beam is converged, in one of opposite directions normal to the surface of the selected storage layer, said one of opposite directions representing the information to be written on said part.

Claim 10

A magneto-optical apparatus for recording information on a magneto-optical memory medium, comprising: at least one light source for emitting a laser beam toward said memory medium, for writing information on selected one of a plurality of magneto-optical storage layers which are separated from each other by at least one non-magnetic layer; an optical device including an object lens positioned opposite to said memory medium, for convering said laser beam; selector means for selecting a focal point of said laser beam on said selected one of the storage layers of the memory medium; and magnetic-field generating means for generating a magnetic field to magnetize a part of said selected one of the storage layers at which said laser beam is converged, in one of opposite directions normal to the surface of the selected storage layer, said one of opposite directions representing the information to be written on said part.

Claim 11

A magneto-optical apparatus according to claim 7, wherein said at least one light source consists of a single laser light source for emitting a single laser beam, and said selector means comprises positioning means for positioning said object lens relative to the memory medium along an optical axis of said object lens, and thereby positioning the focal point of said single laser beam on said selected storage layer of the memory medium.

Claim 12

A magneto-optical apparatus according to claim 7, wherein said at least one light source consists of a plurality of laser light sources for emitting laser beams corresponding to said plurality of storage layers of the memory medium, said optical device including a plurality of stationary object lenses positioned opposite to said memory medium and spaced apart from each other along the surface of the memory medium, for converging said laser beams on said plurality of storage layers, respectively, said selector means comprising a shutter device associated with said laser light sources, for allowing only one of said laser light sources corresponding to said selected storage layer of the medium, to emit the corresponding laser light beam therethrough toward the medium.

Claim 13

A magneto-optical apparatus according to claim 7, wherein said at least one light source consists of a plurality of laser light sources for emitting laser beams corresponding to said plurality of storage layers of the memory medium, said object lens of the optical device being positioned stationary relative to said memory medium and converging said laser beams on said plurality of storage layers, respectively, at the same position as viewed in a plane parallel to the surface of the storage medium, said selector means comprising a power switch which activates only one of said laser light sources to emit the laser beam corresponding to said selected storage layer of the medium.

Claim 14

A magneto-optical apparatus according to claim 7, wherein said at least one light source consists of a single laser light source for emitting a single laser beam, and said selector means comprises positioning means for positioning said single laser light source relative to said object lens along an optical axis of said object lens, and thereby positioning said focal point of said single laser beam on said selected storage layer of the memory medium.

Claim 15

A magneto-optical apparatus for recording information on a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical storage layers having different Curie points, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said plurality of magneto-optical storage layers, said apparatus comprising a laser light source for emitting a laser beam toward said memory medium for writing information on selected one of said plurality of storage layers, said apparatus further comprising means for changing an intensity of said laser beam, to heat said storage layers to different temperatures and thereby prepare for effecting the writing of information selectively on said storage layers of the memory medium.

Claim 16

A magneto-optical apparatus for recording information on a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical storage layers having different Curie points, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said plurality of magneto-optical storage layers, said apparatus comprising a laser light source for emitting a laser beam toward said memory medium for writing information on selected one of said plurality of storage layers, said apparatus further comprising means for changing an intensity of said laser beam, to heat said storage layers to different temperatures and thereby prepare for effecting the writing of information selectively on said storage layers of the memory medium.

Claim 17

A magneto-optical apparatus according to claim 12, wherein said intensity of the laser beam is reduced so as to write the information on the storage layers, in the order of the Curie point of the storage layers, beginning with the storage layer having the highest Curie point.

Claim 18

A magneto-optical apparatus, comprising: a laser light source for emitting a laser beam toward a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical storage layers having different Curie points, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said plurality of magneto-optical storage layers; an optical device including an object lens for converging said laser beam on said memory medium, to heat said storage layers of the memory medium in a direction perpendicular to the surface of the memory medium; means for changing an intensity of said laser beam so that a temperature of said storage layers is changed between a first level higher than the highest Curie point of the storage layers, and a second level lower than said highest Curie point; and magnetic-field generating means for generating a magnetic field to magnetize a part of selected one of the storage layers at which said laser beam is converged, in one of opposite directions normal to the surface of the selected storage layer, said one of the opposite directions representing the information to be written on said part.

Claim 19

A magneto-optical apparatus, comprising: a laser light source for emitting a laser beam toward a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical storage layers having different Curie points, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said plurality of magneto-optical storage layers; an optical device including an object lens for converging said laser beam on said memory medium, to heat said storage layers of the memory medium in a direction perpendicular to the surface of the memory medium; means for changing an intensity of said laser beam so that a temperature of said storage layers is changed between a first level higher than the highest Curie point of the storage layers, and a second level lower than said highest Curie point; and magnetic-field generating means for generating a magnetic field to magnetize a part of selected one of the storage layers at which said laser beam is converged, in one of opposite directions normal to the surface of the selected storage layer, said one of the opposite directions representing the information to be written on said part.

Claim 20

A magneto-optical apparatus for reading information from a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical layers, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said magneto-optical storage layers, said apparatus comprising means for applying to said memory medium a plurality of laser beams of different wavelengths corresponding to said plurality of storage layers, and further comprising means for reading information from selected one of said storage layers of the memory medium, based on a change of corresponding one of said plurality of laser beams which occurs due to magneto-optical anisotropy of the selected storage layer.

Claim 21

A magneto-optical apparatus for reading information from a magneto-optical memory medium which consists of a laminar structure including a plurality of magneto-optical layers, and at least one non-magnetic layer each of which is interposed between adjacent two layers of said magneto-optical storage layers, said apparatus comprising means for applying to said memory medium a plurality of laser beams of different wavelengths corresponding to said plurality of storage layers, and further comprising means for reading information from selected one of said storage layers of the memory medium, based on a change of corresponding one of said plurality of laser beams which occurs due to magneto-optical anisotropy of the selected storage layer.

Claim 22

A magneto-optical apparatus for reading information from a magneto-optical memory medium of a laminar structure, comprising: an optical system including a plurality of laser light sources which emits a plurality of laser beams of different wavelengths corresponding to a plurality of magneto-optical layers of said memory medium which are separated from each other by at least one non-magnetic layer, said optical system further including means for applying said plurality of laser beams, as linearly polarized light beams, to said memory medium; and detecting means for detecting angles of the Kerr rotation of said plurality of laser beams which have been transmitted through or reflected from said memory medium, and detecting changes in the Kerr rotation angles of the laser beams which occur due to magneto-optical anisotropy of said plurality of storage layers of the memory medium, whereby information stored in each of said storage layers is read out by detecting the change in the Kerr rotation angle of the corresponding laser beam.

Claim 23

A magneto-optical apparatus for reading information from a magneto-optical memory medium of a laminar structure, comprising: an optical system including a plurality of laser light sources which emits a plurality of laser beams of different wavelengths corresponding to a plurality of magneto-optical layers of said memory medium which are separated from each other by at least one non-magnetic layer, said optical system further including means for applying said plurality of laser beams, as linearly polarized light beams, to said memory medium; and detecting means for detecting angles of the Kerr rotation of said plurality of laser beams which have been transmitted through or reflected from said memory medium, and detecting changes in the Kerr rotation angles of the laser beams which occur due to magneto-optical anisotropy of said plurality of storage layers of the memory medium, whereby information stored in each of said storage layers is read out by detecting the change in the Kerr rotation angle of the corresponding laser beam.