Static information storage and retrieval – Magnetic bubbles – Detectors
Patent
1984-08-20
1987-02-10
Moffitt, James W.
Static information storage and retrieval
Magnetic bubbles
Detectors
365122, G11C 1908
Patent
active
046427953
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermomagnetic recording system in which the recording of an information on an optical magnetic memory is carried out by the irradiation of light and the information bits thus recorded can be moved to another position.
BACKGROUND ART
There is a known thermomagnetic recording system which uses a layer of soft magnetic material having an easy axis of magnetization normal to the layer surface on which the thermomagnetic recording is performed by irradiating a laser light thereon. The system is disclosed in the publicated document of Japanese Kokai No. 158005/1982 (Japanese patent application, No. 45232/1981) filed by the present applicant. The layer of soft magnetic material having an easy axis of magnetization normal to the layer surface used therein is a layer made of soft magnetic material, for example, YSmCaFeGe-series garnet such as (YSmCa).sub.3 (FeGe).sub.5 O.sub.12 or the like, having uniaxial magnetic anisotropy strong in the direction normal to the layer surface and an easy axis of magnetization normal to the layer surface. The layer of soft magnetic material having an easy axis of magnetization normal to the layer surface is required to have such soft magnetic property that when this layer is used as a recording medium, the diameter of information bits to be written therein is practically determined only by a bias magnetic field, and the coercive force thereof is desired to be less than about 3 Oe, preferably about 1 Oe or below. This layer of soft magnetic material having an easy axis of magnetization normal to the layer surface is formed by growing on a crystalline substrate of rare-earth gallium garnet such as non-magnetic gadolinium gallium garnet (GGG) by the liquid phase epitaxial (LPE) growth of YSmCaFeGe-series garnet crystal or the like. The writing an information on that layer is carried out such that a bias magnetic field of a predetermined strength is first applied to the layer of the soft magnetic material so as to make the layer magnetized to have a single magnetic domain over the whole layer surface thereof and magnetization directed to the direction perpendicular to the layer surface. Then, under this state, when an optical pulse is incident on the layer surface under being focussed thereon, this light energy is converted to heat energy so as to generate heat by which bits (magnetic bubbles) are formed, or the writing of an information on the layer can be carried out. The bits thus written are cylindrical magnetic domains each having a predetermined diameter and the magnetization directed to the direction opposite to the applied bias magnetic field.
The strength of the bias magnetic field applied to the layer of soft magnetic material so as to produce a single magnetic domain therein over the whole layer surface thereof is selected in a range from the run-out magnetic field to the collapse magnetic field of the material, for example, between 57 Oe and 73 Oe for the LPE layer of (YSmCa).sub.3 (FeGe).sub.5 O.sub.12. Because the coercive force, particularly magnetic wall coercive force of the layer of soft magnetic material is extremely small and hence the bias magnetic field applied thereto can be small, the bias magnetic field generating means may be a small solenoid coil, rubber magnet or the like.
The reading-out of the information from the magnetized layer on which the recording was made as above is carried out such that a light, for example, a laser light is linearly polarized by a polarizer and then irradiated on the recorded medium. When the linearly polarized light passes through the magnetized layer, it is subjected to the rotation by the Faraday-effect. Then this rotated light is applied through an analyzer into a photo-detecting means so that the output corresponding to the information bits is produced therefrom and hence the reading-out of the information is performed.
According to the above thermomagnetic recording on the LPE magnetic garnet thin film, since its magnetic wall coercive force Hc is as small as about 1 O
REFERENCES:
patent: 3787825 (1974-01-01), DeJonge
patent: 4012724 (1977-03-01), Hanson et al.
patent: 4149265 (1979-04-01), Gorres et al.
Kaneko Masahiko
Okamoto Tsutomu
Tamada Hitoshi
Yamada Toshiro
Moffitt James W.
Sony Corporation
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