Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-03-31
2002-09-24
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013420, C428S690000
Reexamination Certificate
active
06456571
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Japanese patent application No. HEI 11(1999)-090527 filed on Mar. 31, 1999 whose priority is claimed under 35 USC §119, the disclosure of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates to a magneto-optical recording medium such as a magneto-optical disk, a magneto-optical tape, a magneto-optical card, etc., applied to a magneto-optical recording and reproducing apparatus and to a reproducing method thereof.
BACKGROUND OF THE INVENTION
Hitherto, as a re-writable optical recording medium, a magneto-optical disk using a magneto-optical recording medium has been practically used. In such a magneto-optical disk, by focusing and striking a light beam emitted from a semiconductor laser onto the optical recording medium, the local temperature of the magneto-optical recording medium is raised, whereby recording and erasing are carried out. Also, a light beam of an intensity of not causing recording and erasing is focused and strikes onto a magneto-optical recording medium and by discriminating the polarized light state of the reflected light, the reproduction of the recorded information is carried out. However, in the magneto-optical recording medium of prior art, there is a problem that when the recording bit diameter and the recording bit distance in the recorded magnetic domain become small relative to the beam spot diameter of the light beam, the reproduction characteristics are deteriorated. This is because an adjacent recording bit enters the beam spot of a light beam focused onto the aimed recording bit, it becomes impossible to separate each recording bit and reproduce it.
As a magneto-optical recording medium for solving the above-described problem, a magneto-optical recording medium composed of a reproducing magnetic layer which is in an in-plane magnetized state at room temperature and becomes a perpendicularly magnetized state at a temperature of at least a critical temperature, an in-plane magnetized layer having a Curie temperature near the above-described critical temperature, a non-magnetic intermediate layer, and a recording layer made of a perpendicularly magnetized film and recording an information is proposed (Japanese Patent Laid-Open No. 320134/1997).
However, in the magneto-optical recording medium described above, because the reproducing magnetic layer is in an in-plane magnetized state in the temperature range of lower than the critical temperature, the information of the recording magnetic domain recorded to the recording layer is not transferred to the reproducing magnetic layer and the information of the recording magnetic domain is not reproduced. On the other hand, in the temperature range of at least the critical temperature, the reproducing magnetic layer becomes a perpendicularly magnetized state, the information of the recording magnetic domain recorded to the recording layer is transferred to the reproducing magnetic layer, and the information of the recording magnetic domain is reproduced. Accordingly, even when an adjacent recording bit enters the beam spot of a light beam focused onto the reproducing magnetic layer, the reproducing power of a light beam and the critical temperature at which the reproducing magnetic layer becomes a perpendicularly magnetized state are appropriately established, each recording bit can be separated and reproduced, and an information recorded at a high density can be reproduced.
However, recently, a larger recording capacity has been required for an optical disk but in the magneto-optical recording medium described in Japanese Patent Laid-Open No. 320134/1997 described above, there is a problem that the reproduction resolving power is insufficient.
SUMMARY OF THE INVENTION
The present invention has been made for solving the above-described problem and provides a magneto-optical recording medium which can obtain a high reproduction resolving power, can prevent the occurrence of lowering the reproduced amount of light, and can obtain a reproduced signal of a high quality, and also provides a reproduction method thereof.
That is, according to one aspect of the invention, there is provided a magneto-optical recording medium comprising a recording magnetic layer made of a perpendicularly magnetized film and a multilayer reproducing film, wherein the multilayer reproducing film has two reproducing magnetic layers which are in a in-plane magnetized state at room temperature and shift to a perpendicularly magnetized state with a rise in temperature and an in-plane magnetized layer disposed between the two reproducing magnetic layers, which is in an in-plane magnetized state from room temperature to a Curie temperature and has a lower Curie temperature than the recording magnetic layer and the reproducing magnetic layers.
That is, in the magneto-optical recording medium, the shift of the reproducing magnetic layers from the in-plane magnetized state to the perpendicularly magnetized state becomes more sharp than a magneto-optical recording medium of prior art. Thereby, the limit of the improvement of the reproduction resolving power of prior art is overcome and a higher reproduction resolving power is obtained.
In the magneto-optical recording medium of the invention, it is preferred that the critical temperature of each reproducing magnetic layer for shifting to the perpendicularly magnetized state is established to be almost the same as the Curie temperature of the in-plane magnetized layer adjacent to at least one side of the film thickness direction. In this case, the term “almost the same” means a range of within ±30° C.
Also, in the magneto-optical recording medium of the aspect of this invention, it is preferred that the thickness of each of the reproducing magnetic layers is from 10 nm to 35 nm.
This is because when the thickness thereof is less than 10 nm, the intensity of the reproduction signal is considerably lowered, while the thickness thereof is more than 35 nm, the reproduction resolving power is lowered.
Furthermore, in the magneto-optical recording medium of the aspect of the invention, it is preferred that the in-plane magnetized layer disposed between the reproducing magnetic layers is established to have a thin thickness capable of transmitting a light beam for reproduction through the layer. In this case, it is preferred that the thickness of the in-plane magnetized layer is from 3 nm to 30 nm as described below.
Also, according to another aspect of the invention, there is provided a magneto-optical recording medium comprising a recording magnetic layer made of a perpendicularly magnetized film and a multilayer reproducing film, wherein the multilayer reproducing film comprises at least two reproducing magnetic layers which are in an in-plane magnetized state at room temperature and shift to a perpendicularly magnetized state with a rise in temperature, and an in-plane magnetized layer having a lower Curie temperature than the recording magnetic layer and the reproducing magnetic layers, which is in an in-plane magnetized state from room temperature to the Curie temperature, the reproducing magnetic layers and the in-plane magnetized layer being alternately laminated.
According to another aspect of the invention, there is provided a method of reproducing a magneto-optical recording medium, which comprises using one of the above-described magneto-optical recording medium, irradiating the above-described multilayer reproducing film by a light from the opposite side to the side disposed the recording magnetic layer and reproducing an information using not only the reflected light from the reproducing magnetic layer disposed nearest the light incident side but also the reflected light of the light transmitted through the reproducing magnetic layer and striking the other reproducing magnetic layer.
REFERENCES:
patent: 5982715 (1999-11-01), Mori et al.
patent: 6187460 (2001-02-01), Nishimura
patent: 6400565 (2002-06-01), Tanase et al.
patent: 9-320134 (1997-12-01), No
Hirokane Junji
Iwata Noboru
Conlin, Esq. David G.
Dike, Bronstein, Roberts & Cushman, Intellectual Property Practi
Dinh Tan
Hartnell, Esq. George W.
Sharp Kabushiki Kaisha
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