JPS58153244A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the S/N ratio of a reproduced signal by laminating the 1st and the 2nd magnetic film layer which differ in refractive index on a transparent substrate and utilizing Fraday effect and Kerr effect in combination. CONSTITUTION:On the transparent substrate 5, the 1st magnetic layer 1 and the 2nd magnetic layer 2 are laminated. Both magnetic layers consists of vertically magnetized films which differ in refractive index sufficiently and reproducing light is reflected by the interface between the magnetic layers 1 and 2. The repoducing light A entered from the substrate side 5 is reflected partially by the surface of the 1st magnetic layer 1 and its reflected light B has the plane of polarization rotated by Kerr effect. The transmitted light has the plane of polarization rotated by Faraday effect, and also has the plane of polarization rotated by Kerr effect when reflected by the interface with the magnetic film 2 and the plane of the polarization rotated again by Faraday effect when transmitted through the magnetic film 1 to obtain reflected light C. The directions of rotations bt Faraday effect and Kerr effect are made coincide with each other. Consequently, the reflected light B and reflected light C become to be arithmetically, thereby improving the S/N ratio of reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical recording medium that performs recording using the heat of laser light and performs reproduction using the magneto-optic effect.

Generally, a magneto-optical recording medium is one in which a magnetic thin film is provided on a substrate, and there are two types of reproducing methods for the magneto-optical recording medium: one that utilizes the Faraday effect and another that utilizes the Kerr effect. However, devices that utilize the Faraday effect detect the magnetization direction from the rotation of the plane of polarization due to the transmission of light, and because the light source and detector are located opposite to the recording medium, only one side of the recording medium can be used. In addition, the optical path becomes long, which increases the size of the device. On the other hand, devices that utilize the Kerr effect 1 detect the rotation direction of the plane of polarization due to the reflection of light, and because the light source and detector are located on the same side of the recording medium, recording can be performed on both sides of the recording medium. In addition, although the optical path is shortened and the device can be made smaller, the signal due to the Kerr effect is weak and signal detection is difficult. Furthermore, a method of using the Faraday effect by providing a metal reflective film on the back surface of the recording medium has been considered, but a sufficient reproduction signal-to-noise ratio has not yet been obtained.

The present invention solves these conventional drawbacks,
This is a reflective magneto-optical recording medium having a multilayer structure of magnetic thin films. This configuration has the advantage that it is possible to take advantage of the advantages of the reflection type reproduction method and also to obtain a high reproduction SN ratio.

The playback S/N ratio is 57NC when noise is dominant.
x-, fyτ·θ If amplifier noise is dominant, S/NCX: Io-O. Here, IO is the reproduction optical power reaching the detector,
θ is the rotation angle of the polarization plane of the reproduction light by the recording medium. Therefore, in order to improve the reproduction signal-to-noise ratio, it is important to increase the rotation angle of the polarization plane of the reproduction light and the power of the reproduction light reaching the detector. In the great invention, by making the recording layer made of a magnetic thin film into a multilayer structure, it is possible to effectively prevent the rotation of the polarization plane of the reproduced light due to reflection on the recording medium (Kerr effect) and the rotation of the polarization plane due to transmission (Faraday effect). In combination, the rotation angle of the polarization plane of the reproduction light and the power of the reproduction light reaching the detector can be increased to improve the reproduction S/N ratio.

Hereinafter, the magneto-optical recording medium of the present invention will be explained with reference to drawings of embodiments.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 is a first magnetic layer, 2 is a second magnetic layer, and these first... The second magnetic layers 1 and 2 have a laminated structure, and the transparent substrate 6
is placed above. The two magnetic layers 1 and 2 are composed of perpendicularly magnetized films having sufficiently different refractive indexes, and in this case, the reproduction light is sufficiently reflected at the interface between the two magnetic layers 1 and 2. With this configuration, the reproduction beam incident from the substrate 6 side is partially reflected by the surface of the first magnetic layer 1,
The plane of polarization of the reflected light B is rotated by the Kerr effect. The transmitted light has its plane of polarization rotated by the Faraday effect, reaches the interface with the second magnetic layer 2, is reflected on the surface of the second magnetic layer 2, and upon reflection, the plane of polarization is further rotated by the Kerr effect. Then, the reflected light C reflected by the surface of the second magnetic layer 2 passes back through the first magnetic layer 1, so that the plane of polarization is further rotated by the Faraday effect and exits from the first magnetic layer. Therefore,
Reflected light B on the surface of the first magnetic layer 1 and the two magnetic layers 1 and 2
The sum of the light C reflected at the interface and transmitted through the first magnetic layer 1 is detected. Here, since the Kerr rotation angle direction and Faraday rotation angle direction of the first magnetic layer 1 are selected to match the Kerr rotation angle direction of the second magnetic layer 2, the polarization plane of the reproduction light passing through the two optical paths is The rotation angle and the reproduction light power reaching the detector are additive, and the reproduction signal-to-noise ratio is improved.

FIG. 2 shows an embodiment of the present invention. In FIG. 2, 3 is a first magnetic layer, 4 is a second magnetic layer, and these first... The second magnetic layers 3 and 4 have a laminated structure and are provided on the transparent electrode 5. The two magnetic layers 3 and 4 are composed of perpendicularly magnetized films having a small difference in refractive index.

In this case, since the reflected light on the surface of the second magnetic layer 4 is reduced, there is a gap between the two magnetic layers 3.4 that is transparent to the reproduction beam and has a refractive index sufficiently different from that of the second magnetic layer 4. A thin film substance 6 is provided to increase the reflected light C on the surface of the second magnetic ridge 4 to enhance the effect. With this configuration, the reproduction beam B incident from the substrate 6 side is partially reflected by the surface of the first magnetic layer 3, and the plane of polarization of the reflected beam B is rotated due to the Kerr effect. The plane of polarization of the transmitted light rotates due to the Faraday effect, and reaches the interface with the second magnetic layer 4 via the thin film material layer 6, and the polarization plane of the transmitted light rotates.
The plane of polarization is further rotated by the Kerr effect upon reflection. Then, since the reflected light C reflected by the surface of the second magnetic layer 4 passes back through the first magnetic layer 3, the plane of polarization further rotates due to the Faraday effect, and
It comes out of the magnetic layer 3. Therefore, the sum of the light B reflected on the surface of the first magnetic layer 3 and the light C reflected at the interface between the two magnetic layers 3.4 and transmitted through the first magnetic layer 3 is detected.

Here, since the Kerr rotation angle direction and the Faraday rotation angle direction of the first magnetic layer 3 are selected to match the Kerr rotation angle direction of the second magnetic layer 4, the polarization plane of the reproduction light passing through the two optical paths is The rotation angle and the reproduction light power reaching the detector are additive, and the reproduction signal-to-noise ratio is improved.

Specifically, glass was used as the transparent substrate 6, Gd Tb Fe was sputtered on it to a thickness of 26 OA as the first magnetic layer 3, SiO2 was evaporated to a thickness of 100 Å as the transparent film material 6, and then On top of that, Gd Tb Fe is sputtered as a second magnetic layer 4 to a thickness of 3ooX.
As a result of measuring the reproduction S/N ratio of the magneto-optical recording medium with the provided structure, it was found that it was approximately e dB lower than that of the medium with a single recording magnetic layer.
An improvement was obtained.

As described above in detail, according to the present invention, the recording magnetic layer is
By effectively combining the Kerr effect and Faraday effect of each layer, it has the advantage that the reproduction S/N ratio of a conventional magneto-optical recording medium with a single recording magnetic layer can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing one embodiment of the invention, and FIG. 2 is a sectional view of a magneto-optical recording medium showing another embodiment of the invention. 1.3...First magnetic layer, 2,4...Second magnetic layer, 6...Transparent substrate, 6...Transparent thin film material.

Claims (2)

[Claims] (1) A magneto-optical recording medium in which a recording layer with a multilayer structure consisting of a first magnetic layer and a second magnetic layer having different refractive indexes is provided on a transparent substrate. (2) A recording layer with a multilayer structure consisting of a first magnetic film layer and a second magnetic film layer is arranged such that the Kerr rotation direction of the first magnetic layer located on the reproduction light incident side, the Faraday rotation direction of the first magnetic layer, and the Faraday rotation direction of the first magnetic layer are The first magnetic layer is composed of two perpendicularly magnetized films in which the Kerr rotation directions of the two magnetic layers coincide with the wavelength of the reproducing light, and the first magnetic layer has a film thickness that provides sufficient transmission for the reciprocating reproducing light. , the second magnetic layer is transparent to direct or reproduction light;
2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is configured to be in contact with the first magnetic layer via a thin film material having a different refractive index from that of the magnetic layer.