JPH07320319A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium in which the CNR of reproduced signal is enhanced by reducing the noise caused by the disordered magnetizing direction or the crosstalk noise caused by reading up to the noncentral part of a laser spot. CONSTITUTION:An exchange coupling magnetic layer comprises a recording layer (vertical magnetization film) 5, and a first magnetic layer of in-plane magnetization film (reproduction layer) 4. A second magnetic layer of in-plane magnetization film 3 having such transmittance as allowing the laser light entering from the substrate 1 side to be reflected on the exchange coupling magnetic layer and returned back to the substrate 1, is provided between the exchange coupling magnetic layer and the the substrate 1. The initial magnetizing direction of the reproduction layer 4 is oriented in the in-plane direction by the second magnetic layer 3 magnetized in the in-plane direction within the temperature range from room temperature to the Curie point or Neel temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention comprises an exchange-coupling magnetic layer comprising a recording layer (= perpendicular magnetic film) and a reproducing layer (= in-plane magnetic film at room temperature). The present invention relates to a magneto-optical recording medium that achieves high recording density by transferring and reading.

[0002]

2. Description of the Related Art Magneto-optical recording media have been attracting attention as rewritable recording media with large storage capacity and high reliability, and they have been put to practical use in various fields including computer memories and have become popular. There is. However, with the increase in the amount of information and downsizing of equipment,
There is a demand for higher density recording / reproducing technology.

The high-density recording / reproducing technique is composed of a device-side technique and a medium-side technique. As the former technique,
There are techniques such as an optical super-resolution method for obtaining a focused spot that exceeds the diffraction limit of laser light and a technique for shortening the wavelength of laser light.
The latter technologies include narrowing the pitch of media and improving reproduction resolution by magnetic multilayer film (Proceedings of Magnet
to-Optical Recording International Symposium '92,
J.Magn.Soc.Jpn., Vol.17, Supplement No.S1 (1993), pp.2
(See 01-204). Here, the technique for improving the reproduction resolution by the magnetic multilayer film utilizes the fact that the temperature distribution of the laser spot has the highest Gaussian distribution in the vicinity of the center of the recording layer (= perpendicular magnetization film). In this technique, the state of the reproducing layer is read by selectively transferring the state to the reproducing layer (= in-plane magnetized film at room temperature).

[0004]

In a magneto-optical recording medium in which the state of the recording layer is selectively transferred to the reproducing layer by raising the temperature at a laser spot, the influence of the fact that the recording layer is a perpendicular magnetization film is considered. Therefore, the magnetization direction of the reproducing layer in contact with the recording layer is not a perfect in-plane direction in the initial state. Therefore, when reading the state transferred to the reproducing layer, noise caused by the disordered magnetization direction and even the state of the non-center portion (the peripheral low temperature portion) of the laser spot are read. This causes crosstalk noise, which causes a problem that CNR (Carrier to Noise Ratio) is lowered. An object of the present invention is to improve the CNR of a reproduced signal by reducing the above noise.

[0005]

According to a first aspect of the present invention, a recording layer, which is a perpendicular magnetization film, and a first surface on which the magnetization direction of the recording layer is transferred by being heated to a predetermined transfer temperature. In a magneto-optical recording medium having an exchange-coupling magnetic layer composed of an in-plane magnetic film magnetic layer, a second in-plane magnetic film magnetic layer for transmitting light is provided on the first in-plane magnetic film magnetic layer. It is a magneto-optical recording medium characterized by the above. In the above description, the predetermined transfer temperature means the first in-plane magnetic film magnetic layer (reproducing layer).
The temperature at which the direction of the magnetization changes from the in-plane direction to the vertical direction.

A second aspect of the present invention is the magneto-optical recording medium, wherein the Curie temperature or the Neel temperature of the second in-plane magnetic film magnetic layer of the first aspect is lower than the transfer temperature. According to a third aspect of the present invention, the second in-plane magnetized magnetic film layer according to the second aspect is
It is a magneto-optical recording medium composed of a NiO film of 30 Å or more.

[0007]

According to the first aspect of the invention, the second in-plane magnetic film magnetic layer is provided on the surface opposite to the first in-plane magnetic film magnetic layer (reproducing layer) in contact with the recording layer (perpendicular magnetic film). Therefore, despite the influence of the magnetization of the recording layer, the magnetization direction of the first in-plane magnetic film magnetic layer in the initial state is aligned with the in-plane direction. According to the second aspect of the present invention, the Curie temperature or the Neel temperature of the second in-plane magnetic film magnetic layer is lower than the transfer temperature, so that the magnetization disappears at the time of reproducing information. In the invention of claim 3, an example of a suitable material and a suitable thickness of the second in-plane magnetized film magnetic layer is given.

[0008]

EXAMPLE FIG. 1 is a sectional view schematically showing the structure of a magneto-optical recording medium of an example. That is, the transparent substrate 1 made of polycarbonate has a thickness of 800 in this order from the substrate 1 side.
[Å] SiN high refractive index layer 2, thickness 500
The second in-plane magnetized magnetic film layer 3 made of [Å] NiO, the first in-plane magnetized magnetic film layer (reproducing layer) 4 made of GdFeCo having a thickness of 500 [Å], and the thickness 1000 [Å] TbFe
A recording layer 5 made of Co, an antioxidant layer 6 made of SiN having a thickness of 1000 [Å], and a protective layer 7 made of an ultraviolet curable resin having a thickness of about 20 [μm] are formed. Note that this structure can be manufactured by using a conventionally known sputtering method or the like.

In the above, the recording layer 5 which is a perpendicular magnetization film
And the first in-plane magnetic film magnetic layer (reproducing layer) 4 which is an in-plane magnetic film at room temperature are magnetically coupled, and these two layers form an exchange coupling magnetic layer. That is, the substrate 1
When a laser spot is incident from the side to raise the temperature of the first in-plane magnetized film magnetic layer (reproducing layer) 4 to a predetermined transfer temperature,
The direction of the magnetization of the recording layer 5 is transferred to the first in-plane magnetic film magnetic layer (reproducing layer) 4 at a portion exceeding the transfer temperature (130 ° C. in this example). By utilizing this phenomenon, the information of the recording layer 5 is reproduced in the present magneto-optical recording medium. In addition,
Setting the transfer temperature to 130 ° C. as described above can be realized here by adjusting Gd: FeCo to 25:75 [at%].

In the second in-plane magnetic film magnetic layer 3 made of NiO, the room temperature to the nail temperature (10 in this example).
In the temperature range up to 0 ° C., the direction of magnetization exists in the plane. As the laser light transmittance of the second in-plane magnetized magnetic film layer 3, the laser light incident from the substrate 1 side is at least the first in-plane magnetized magnetic film layer of the exchange coupling magnetic layer. The transmittance is required to be reflected by the (reproduction layer) 4, returned to the substrate 1, and detected by a photodetector (not shown) in the subsequent stage. On the other hand, in the second in-plane magnetized film magnetic layer 3,
It is required to fulfill the function of aligning the magnetization direction of the first in-plane magnetized film magnetic layer (reproducing layer) 4 in the in-plane state in the initial state (when the temperature is not raised). Under these circumstances, the thickness of the second in-plane magnetized magnetic film layer 3 made of NiO should be 30 [Å] or more.

Regarding the magneto-optical recording medium of this embodiment and the conventional magneto-optical recording medium (the magneto-optical recording medium having the structure shown in FIG. 2; the structure without the second in-plane magnetic film magnetic layer 3 in FIG. 1), When the CNR of each reproduction signal was measured, the CNR of the magneto-optical recording medium of this example was 3 [dB] better than the CNR of the conventional magneto-optical recording medium. It is considered that the reason is that the noise due to the disordered magnetization direction and the crosstalk noise due to reading out even to the peripheral portion of the laser spot are reduced. Further, when the curl rotation angles of the magneto-optical recording medium of this example and the conventional magneto-optical recording medium were measured, as shown in FIG.
In the low temperature part up to a certain extent, the curve rotation angle of the magneto-optical recording medium of this example was a value sufficiently smaller than that of the conventional one. That is, it was effectively prevented that the magnetization state of the recording layer was read in the low temperature portion.

In the above embodiment, NiO is used as the second in-plane magnetized magnetic layer 3, but instead of this, for example, CoNiO, CoO, MnFe, FeCr, FeN.
Even when i, MnNiPtCo, PdCo, etc. are used, N
The same effect as in the case of iO can be obtained.

[0013]

As described above, according to the first aspect of the invention, the magnetization direction of the first in-plane magnetic film magnetic layer (reproducing layer) in the initial state is as follows.
They are aligned in the in-plane direction despite the influence of the recording layer. Therefore, at the time of reproducing information, noise caused by the disordered magnetization direction and crosstalk noise caused by reading the peripheral portion of the laser spot are reduced, and the CNR of the reproduced signal is improved. According to the second aspect of the invention, the magnetization of the second in-plane magnetized film magnetic layer disappears when the information is reproduced. Therefore, a reproduction signal having a better CNR can be obtained. Further, the invention of claim 3 provides an example of a suitable material and a suitable thickness of the second in-plane magnetized film magnetic layer.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a magneto-optical recording medium of an example.

FIG. 2 is a schematic sectional view of a conventional magneto-optical recording medium.

FIG. 3 is a characteristic diagram in which the car rotation angles of the example and the conventional example are measured at each temperature.

[Explanation of symbols]

 1 Transparent Substrate (Polycarbonate) 2 High Refractive Index Layer (SiN) 3 Second In-Plane Magnetization Film Magnetic Layer (NiO) 4 First In-Plane Magnetization Film Magnetic Layer (Reproducing Layer: GdFeCo) 5 Recording Layer (TbFeCo) 6 Antioxidant layer (SiN) 7 Protective layer (UV curable resin)

Claims (3)

[Claims] 1. An exchange comprising a recording layer which is a perpendicular magnetization film, and a first in-plane magnetization film magnetic layer which is transferred to a magnetization direction of the recording layer by being heated to a predetermined transfer temperature. A magneto-optical recording medium having a coupling magnetic layer, wherein a second in-plane magnetic film magnetic layer that transmits light is provided on the first in-plane magnetic film magnetic layer. media. 2. The magneto-optical recording medium according to claim 1, wherein the Curie temperature or the Neel temperature of the second in-plane magnetic film magnetic layer is lower than the transfer temperature. . 3. The magneto-optical recording medium according to claim 2, wherein the second in-plane magnetized film magnetic layer is a NiO film having a thickness of 30 Å or more.