JPS60119648A - Photo-magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the S/N by forming a soft magnetic thin film through coating transparent to a reproduced light onto a magnetic recording layer. CONSTITUTION:A magnetic recording layer, i.e., a vertical magnetizing film 12 is formed on a base 11 and the soft magnetic thin film 13 transparent to the reproduced light is formed onto the film 12 by the vapor deposition or sputtering through film coating. A planer magnetization 15 having a pattern corresponding to the magnetizing distribution 14 of the film 12 is produced to the film 13 and a component 17 magnetized vertically from the relation of flow of magnetic flux exists at a part surrounded by a circle shown in broken lines. In irradiating a laser light to the part 16 surrounded by a circle in broken lines at reproduction while being subject to linear polarization 5 by a polarizer, the light is transmitted twice so as to be reciprocated through the film 13 at incidence and reflection and the light is subject to rotation twice by the Farady effect. Moreover, a reflected light 5' is reflected on the surface of the film 12 and subject to the rotation due to the magnetic Kerr effect. Thus, the polarized plane rotating angle theta as a whole is the sum of them above thereby improving the S/N at reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical recording medium in which information recorded magnetically or magneto-optically is optically reproduced using the magneto-optical effect.

BACKGROUND TECHNOLOGY AND PROBLEMS In recent years, research on high-density optical recording systems using perpendicularly magnetized films has been actively conducted. In this method, for example, as shown in Figure 1, a magnetic medium (3) consisting of a perpendicularly magnetized film (2) formed on a substrate (11) is irradiated with light onto the surface of the perpendicularly magnetized film (2). Then, by partially heating a part of the perpendicularly magnetized film (2) to a temperature higher than the magnetic Curie temperature or magnetization compensation temperature, and then cooling it, a magnetized region in the opposite direction to the surrounding magnetization direction is created, and as a result, light is emitted. Information is recorded by creating a magnetization reversal region (4) corresponding to the beam signal.The principle behind this is that the coercive force of perpendicular magnetization lll!+2) is L.
It takes advantage of the fact that the temperature changes significantly around the temperature shown below. To reproduce the information recorded in this way, for example, a laser beam is turned into linearly polarized light (6) by a polarizer and is irradiated directly onto the perpendicularly magnetized film (2), and the plane of polarization is rotated by reflection from the film surface. This reflected light (
5') is detected through an analyzer. It is known that the S/N ratio of the reproduced signal (optical signal) at this time is proportional to the rotation angle of this plane of polarization, that is, the Kerr rotation angle.

Conventionally, the perpendicular magnetization film (21) used in such a recording medium (3) is made of GdCo, GdFe+TbPe, etc., but in each case, the Kerr rotation angle θ is 0.3° to 0.3°.
It is about 4° (18 to 24 minutes). Therefore, there is a limit to the S/N ratio of reproduced information.

On the other hand, it is also possible to use a CoCr film as the perpendicular magnetization film (21) for magnetic recording and optical reproduction as described above. However, the Kerr rotation angle θ of this CoCr film is approximately 5 minutes. , the S/N ratio is poor.

Purpose of the Invention In view of the above-mentioned points, the present invention provides a method for storing recorded information in a large S.
The object of the present invention is to provide a magneto-optical recording medium that can perform optical reproduction at a /N ratio.

Summary of the Invention The present invention is a magneto-optical recording medium comprising a magnetic recording layer (so-called perpendicular magnetization film) on which a soft magnetic thin film transparent to reproduction light is deposited.

In the magneto-optical recording medium of the present invention, during optical reproduction, the S/N ratio can be improved by the rotation of the plane of polarization due to the Kerr effect of the magnetic recording layer and the rotation of the plane of polarization due to the Faraday effect of the soft magnetic VW film.

EXAMPLE Hereinafter, an example of the magneto-optical recording medium according to the present invention will be explained using FIGS. 2 and 3.

In the present invention, as shown in FIG. 2, basic treatment (11)
A magnetic recording layer, that is, a perpendicular magnetization film (12) is formed thereon, and further, for example, vapor deposition is performed on this perpendicular magnetization film (2).

A soft magnetic thin film that is transparent to reproduction light by sputtering etc.
13) is formed by depositing. In the case of magneto-optical recording, the perpendicular magnetization film (12) is, for example, GdCo.

A film of GdFe, TbFe, etc. can be used. The soft magnetic thin film (13) is used to transfer a magnetization pattern corresponding to the magnetization bit information recorded on the perpendicular magnetization film (12). Use materials. In the case of metal, the thickness of the soft magnetic thin film (13) is such that the light absorption coefficient is 105 cm-
1, which is extremely large, so in order to be transparent to reproduction light, that is, to obtain a suitable polarized light intensity, it is desirable that the thickness be 100 Å or less.

When the soft magnetic wt film (13) is formed on the perpendicularly magnetized film (12) by vapor deposition, sputtering, etc., this film (13)
A pattern of in-plane magnetization (15) corresponding to the magnetization distribution (14) of the perpendicularly magnetized film (12) is generated. In particular, in the portion (16) surrounded by the broken line circle in FIG. 2, there is a perpendicularly magnetized component (17) due to the flow of magnetic flux lines. Therefore, during reproduction, the laser beam is linearly polarized by a polarizer and incident on the area (16) surrounded by the broken line circle, and the reflected light is detected through an analyzer. At this time, as shown in FIG. 3, the linearly polarized light (5) passes through the soft magnetic* film (13) twice by being incident and reflected back and forth, and is thus rotated twice by the Faraday effect. Further, the reflected light (5') is reflected by the surface of the perpendicular magnetization IQ (12) and is therefore rotated by the magnetic Kerr effect. Therefore, the overall polarization plane rotation angle θ
is θ=θ+2θF (where θ is the Kerr rotation angle of the perpendicularly magnetized film (12)).

θF is the Faraday rotation angle of the soft magnetic thin film (13). It becomes one.

The Faraday rotation angle θF of each film of Fe, permalloy, and Co with respect to light with a wavelength of 500 to 546 nm is shown in the table.

Table 1 - As is clear from this table, the Faraday rotation angle 2θF in the soft magnetic thin film (13) is, for example, in the case of Fe, 0.8 deg (48 minutes) for 100 people and 0.4 deg for 50 people.
(24 minutes). These 2θ de are perpendicular magnetization ll1(
12) is added to the Kerr rotation angle θK, thereby improving the S/N ratio during reproduction.

In addition, on the upper side, the perpendicular magnetization 1m (12) is (+dCo, G
dFe.

It was composed of magneto-optical recording material such as TbFe, but other materials such as Co
It may also be made of a magnetic recording material such as Cr. In this case, recording is performed magnetically and reproduction is performed optically, resulting in non-contact reproduction. In this case as well, the polarization plane rotation angle is +
It is 2θF.

Effects of the Invention As mentioned above, according to the present invention, by forming a soft magnetic thin film transparent to reproduction light on the perpendicular magnetization ridge,
During optical reproduction, the rotation angle of the plane of polarization increases due to the combination of the rotation due to the magnetic Kerr effect of the perpendicularly magnetized film and the rotation due to the Faraday effect of the soft magnetic thin film, making it possible to improve the S/N ratio. Also, in the case of perpendicular magnetic recording such as CoCr film,
Optical regeneration can improve specific contact regeneration.

[Brief explanation of drawings]

- Fig. 1 is a sectional view showing an example of a conventional magneto-optical recording medium, Fig. 2 is a sectional view showing an embodiment of a magneto-optical recording medium according to the present invention, and Fig. 3 is a main part for explaining the operation of the present invention. FIG. (11) is a substrate, (12) is a magnetic recording layer, and (13) is a soft magnetic thin film.

Claims (1)

[Claims] A magneto-optical recording medium in which a soft magnetic thin layer that is transparent to reproduction light is formed on a magnetic recording layer.