JPS6122454A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To attain high-density recording and to obtain excellent storage stability by providing the 1st magnetic layer having magnetic anisotropy vertical to a film face where a transition metal element is scattered to a dielectric on a substrate and the 2nd magnetic layer having a high coercive force and similar magnetic anisotropy on it. CONSTITUTION:The medium consists of a transparent substrate (a) and thin films 1.2 where metal elements of >= one kind of transition metals formed on the substrate (a) or one kind of rare-earth metals are scattered in the dielectric, and the films 1.2 have the 1st magnetic layer 1 having the direction of magnetic anisotropy vertical to the film face and the 2nd magnetic layer 2 having the magnetic anisotropy vertical to the film face having a higher coercive force than that of the layer 1 provided on the layer 1. A part of the light is absorbed into the layer 1 by irradiating laser light from the substrate (a), a part of the light is transmitted and absorbed into the layer 2 while being reached to the layer 2. Thus, the temperature of the layer 2 rises and the inversion of magnetization is caused. Since the coercive force of the layer 1 is weaker than that of the layer 2, the magnetization of the layer 1 is inverted, a bit is recorded and the recorded bit of the layer 1 is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a magneto-optical recording medium that records, reproduces, and erases information using laser light.

[Prior art]

Conventionally, MnB1-based materials, garnet-based materials, rare earth-transition metal amorphous materials, and the like have been known as materials for magneto-optical recording media used in magneto-optical recording.

The MnBi system has a high Curie temperature, so it requires a high-output laser for recording, and it also has the disadvantage that it has a lot of grain boundary noise, making it impossible to reproduce with a high S/N ratio. Since the light transmittance is high, there is a drawback that a high output laser is required for recording. Among them, the island earth-transition metal amorphous system is
It is expected that it will compensate for the shortcomings of both.

As a reproduction method for such a magneto-optical recording medium, there is a method that utilizes the Faraday effect and the Kerr effect. In the Kerr effect reproduction method, in order to increase the Kerr rotation angle and improve the reproduction signal level, a dielectric layer such as SiO or 5i02 is formed on the magnetic recording layer and multiple reflections on the surface of the magnetic recording layer are utilized. has been considered. Also, Unexamined Japanese Patent Publication No. 55-6
As disclosed in Japanese Patent Application Laid-Open No. 58-6542, by making the magnetic recording layer thinner and forming a metal reflective layer on the back surface, the Kerr rotation angle can be adjusted using the Kerr effect and Faraday effect. Methods for increasing this are also known. on the other hand,
There is also a method of increasing the Kerr rotation angle and improving the reproduction signal level by laminating a magnetic layer with a relatively large Kerr rotation angle such as GdCo or GdFe and a magnetic layer with a large coercive force such as DyFe or TbFe. It is being

Although attempts have been made to increase the Kerr rotation angle and improve the reproduced signal level, these methods are still not satisfactory. Furthermore, the stability of recorded bits is easily affected by the magnitude of the bias magnetic field, and in order to record stable bits, it is necessary to perform recording by applying an optimum/heyas magnetic field.

Further, the magnetic recording layer as described above is easily oxidized when left in a high temperature and high humidity atmosphere in the presence of oxygen. In particular, when the magnetic recording layer is made thinner, the extent of the problem is remarkable. Therefore, as time passes, disadvantages such as a decrease in recording sensitivity of the medium, an increase in errors during recording and reproduction, and signal deterioration tend to occur.

[Disclosure of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a magneto-optical method that can provide a high reproduction signal level, form stable recording bits, and, as a result, enable high-density recording. The goal is to provide recording media.

Another object of the present invention is to provide a magneto-optical recording medium with excellent storage stability. This object can be achieved by the following magneto-optical recording medium of the present invention. That is, the magneto-optical recording medium of the present invention comprises a transparent substrate and a thin film formed on the substrate in which one or more transition metals or one or more rare earth metals are dispersed in a dielectric material. A first magnetic layer having magnetic anisotropy in the direction perpendicular to the film surface, and a thin film formed on the first magnetic layer and having a higher coercive force than the first magnetic layer. and a second magnetic layer having magnetic anisotropy.

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

FIG. 1 is a schematic sectional view showing a basic aspect of the present invention. In this figure, a is a translucent substrate made of plastic, ivy, glass, or the like. 1 is a first magnetic layer having an axis of easy magnetization perpendicular to the thickness direction in which a metal element of one or more groups of transition metals or rare earth metals is dispersed in a dielectric material. For example, one or more metal elements of transition metals such as Fe, Go, Ni, or Gd, Tb,
One type of rare earth metal such as DY 1. The metal element of AIN,
Si3N, , MgF2. BiF3. Sin.

5i02, TiO2, and Ta205 dispersed in a dielectric material made of one or more selected from the group consisting of Ta205.

The volume ratio (volume filling factor: q) of the transition metal or rare earth metal contained in the dielectric is preferably 0.5≦q≦0.95. If the volume filling factor q is less than 0.5, it will be difficult for magnetization with perpendicular magnetic anisotropy to exist stably in the thickness direction, and if q is more than 0.85, the magnetization will be affected by the atmosphere such as oxygen and moisture. This is because the magnetic layer becomes easily oxidized. Within this preferable range of volume filling ratio, it is preferable to set the film thickness, volume filling ratio, etc. so that the light absorption rate of the first magnetic layer with respect to recording light is about 30 to 40%.

The optimum film thickness varies depending on the material of the magnetic layer and the filling rate, but is usually set in the range of 250 to 1000. As will be described later, the light absorption rate has a large effect on the recording and reproducing performance of this recording medium.

Considering the preferable volume filling factor, film thickness and light absorption rate of the first magnetic layer 1 as explained below, each raw material constituting the first magnetic layer 1 is used as a multi-source vapor deposition source, - sputtering method,
The first magnetic layer 1 can be formed by forming a film on the substrate using an ion blasting method, an electron beam evaporation method, or the like.

2 is a second magnetic layer that has a higher coercive force than the first magnetic layer 1 and has magnetic anisotropy in the thickness direction; for example, F
transition metals such as e, Go, Ni, and Gd.

Metal thin film made of one or more metal elements arbitrarily selected from rare earth metals such as Tb and DY, barium ferrite thin film (Baje204), co/held chromium alloy thin film (Go-C:r), manganese-bismuth system A magnetic thin film such as an alloy thin film (MnBi, Mr+C:uBi) can be used.

A film is formed on the first magnetic layer l by a film forming method such as a sputtering method, an ion blasting method, an electron beam evaporation method, etc. using the four raw material metals or ferrites constituting such magnetic thin film components as a multi-source vapor deposition source. The second magnetic layer 2 can be formed by the following steps. The thickness of the second magnetic layer 2 varies depending on the material, but is preferably about 500A to 2000A.

FIG. 2 is a schematic cross-sectional view showing another embodiment of the magneto-optic recording medium of the present invention. This recording medium is constructed by forming an antireflection layer between the substrate a and the first magnetic layer l of the magneto-optic recording medium shown in FIG. 1, and forming a protective layer 3 on the second magnetic layer 2. The antireflection layer to be used is made of a dielectric material whose film thickness is set to have an antireflection structure that minimizes the reflectance on the surface of the first magnetic layer, and can be formed by the same method as the magnetic layer. This antireflection layer functions to efficiently apply laser light to the magnetic layer by reducing reflected light from the surface of the first magnetic layer when laser light is incident thereon.

The protective layer 3 is made of an organic polymer film, an inorganic material such as an oxide or a sulfide, or a metal material, and has the effect of improving the storage stability of the magnetic layer. If the material is organic, this protective layer 3 can be formed by various coating methods such as plasma polymerization, and if the material is inorganic, it can be formed by the same method as for the magnetic layer.

As shown in this magneto-optical recording medium, the first magnetic layer l does not necessarily have to be formed in direct contact with the substrate a.

Further, as shown in FIG. 3, a protective plate a' may be bonded to the magneto-optical recording medium of the embodiment shown in FIG. 2 via an adhesive layer 4.

Furthermore, a configuration in which magnetic layers are provided on both sides of the magneto-optical recording medium is also possible so that recording and reproduction can be performed on both sides of the magneto-optical recording medium.

ψThe recording and reproducing mechanism of the magneto-optical recording medium of the present invention will be explained using the recording medium shown in FIG.

When this recording medium is irradiated with a laser beam from the substrate a side, the light absorption rate of the first magnetic layer is 30 to 40, as described above.
%, the remaining portion of this laser light passes through the first magnetic layer 1, reaches the $2 magnetic layer 2, and is absorbed. Therefore, in the second magnetic layer 2, most of the optical energy is converted into thermal energy, the temperature of the second magnetic layer increases, and when the temperature reaches the main point, the magnetization of the second magnetic layer is reversed.

Since the coercive force of the first magnetic layer l is smaller than the coercive force of the second magnetic layer 2, the magnetization of the first magnetic layer is also reversed with this magnetization reversal, and a bit is recorded. In this way, the second magnetic layer 2 facilitates the magnetization reversal of the first magnetic layer l, and at the same time
enables stabilization of recording bits.

The bits recorded in this manner are reproduced by irradiating the recording medium with laser light from the substrate a side and detecting the polarization angle of the reflected light.

A portion of the irradiated laser beam is reflected by the first magnetic layer 1, and a portion thereof is transmitted and reflected by the second magnetic layer 2. A combination of these two reflected lights is detected during reproduction. The laser light reflected by the first magnetic layer 1 is affected by the Kerr effect of this layer 1, and [the laser light transmitted through the first magnetic layer 1 and reflected by the second magnetic layer 2] and the Kerr effect of the second magnetic layer 2. Since a combination of these respective reflected lights is detected during reproduction, the apparent Kerr rotation angle increases and a high reproduction signal level can be obtained.

Furthermore, when the Curie point of the second magnetic layer 2 is low and there is a risk that the magnetization will be reversed by the reproducing light, a configuration in which the reproducing light does not reach the second magnetic layer 2 is also possible. In this case, a material with a large Kerr rotation angle may be used for the first magnetic outer layer 1, and reproduction may be performed by detecting only the reflected light from the first magnetic layer 1.

As is clear from the examples described below, the magneto-optical recording medium of the present invention having such a first magnetic layer and a second magnetic layer has a stable recording medium without being affected by the bias magnetic field applied during recording. Recording bits can be formed and storage stability is improved.

The magneto-optical recording medium according to the present invention will be explained in more detail by giving examples.

Example 1 Cobalt (Go) was deposited in -silicon oxide (Sin) on a slide glass substrate of 76×26m++
) was formed into a film in which the first magnetic layer was dispersed. This film formation was carried out in plasma by the ion blating method from a dual vapor deposition source of SiO and Go. SiO
The volume filling factor of Go contained in is 0.60,
The film thickness is approximately 450 mm. On top of this, Tb, Dy,
An Fe thin film was formed as the second magnetic layer. This was fabricated by a sputtering method to have a thickness of about 1000 A, and a coercive force of about 3 KOe. A wave 1i of 833 nm was applied to this magneto-optical recording medium from the substrate side, and He with an output of 20 mW was applied.
- Irradiate with Ne laser light and perform 1OKO perpendicular to the thickness direction.
As a result of measuring the Kerr rotation angle with a magnetic field of e applied, both θ were 1.0°.

[Example 2] On a disk-shaped glass plate with a diameter of 2001111 and a thickness of 1.5 cm, He-
A zirconia thin film was formed to a thickness of approximately 800 nm to provide an antireflection structure for Ne laser wavelength of 633 nm. Next, a first magnetic layer and a second ai layer were formed thereon in the same manner as in Example 1.
After forming a 0OA 1'SiO protective layer, a glass protective plate was attached using an adhesive to produce a magneto-optical recording medium.

This magneto-optical recording medium was irradiated with a laser beam from the substrate side for recording.The light source was a He-
A bias magnetic field was applied in the thickness direction of the magnetic layer using a Ne laser. This disk-shaped magneto-optical recording medium
While rotating at 00 rpa+, the magnetic layer was uniformly magnetized, and a laser pulse was oscillated to record a signal at a frequency of 2 MHz. The bias magnetic field applied at this time is
0. ! liK[le. Apply this to He of the output cuff mW.
-Results of reproduction using a Ne laser.

When the recording frequency was 2 MHz, a reproduced signal of about 300 mV was obtained, and the signal waveform was good. Furthermore, recording was performed while changing the bias magnetic field in the range of 0.4 to 0.8 KOe, and the recorded bits were observed under a microscope. As a result, the recorded bits remained stable despite changes in the bias magnetic field. This was confirmed. In addition, we conducted a storage stability test by leaving this magneto-optical recording medium in an atmosphere with a temperature of 45°C and a humidity of 85% R, H, and measuring the change in coercive force over time. It was found that the coercive force hardly decreased and the storage stability was superior to that of conventional magneto-optical recording media.

In addition, as the first magnetic layer, one or more of Fe, Go, old or one or more of Gd, Tb, Dy may be used as AIN, S
i3N, .

MgF2, BiF3, SiO,5i02,
Similar experiments were carried out by fabricating various magneto-optical recording media using the above-mentioned metal thin film or ferrite thin film as the second magnetic layer, using one or more of TiO2 and Ta2O5 dispersed in a dielectric material. However, it was found that the reproduced signal level was high, the stability of the recorded bits was hardly affected by the bias magnetic field, and the storage stability was further improved.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are schematic cross-sectional views showing embodiments of the magneto-optical recording medium according to the present invention. a...Substrate ao...Protective plate b...Reflective anti-city layer 1...First magnetic layer 2...Second magnetic layer
3...Protective layer 4...Adhesive layer Fig. 1 Fig. 2 Fig. 3

Claims (1)

[Claims] It consists of a transparent substrate and a thin film formed on the substrate in which one or more transition metals or one or more rare earth metals are dispersed in a dielectric material, and has magnetic anisotropy in the direction perpendicular to the film surface. and a second magnetic layer formed on the first magnetic layer and made of a thin film having a higher coercive force than the first magnetic layer and having magnetic anisotropy in the direction perpendicular to the film surface. A magneto-optical recording medium comprising at least one magneto-optical recording medium.