JPS6122455A - Magnetooptic recording medium - Google Patents

Abstract

PURPOSE:To attain high-density recording and excellent storage stability by providing the 1st magnetic layer having a magnetic anisotropy vertical to a film face where a transition metal element is scattered to a dielectric to a substrate and the 2nd magnetic layer having a higher coercive force and similar magnetic anisotropy onto the 1st layer. CONSTITUTION:A metal element such as transition metal Fe or a rare earth metal such as Gd is scattered to the dielectric such as SiO2 on a transparent substrate (a) and a magnetization anisotropy is given vertically to the film face to form the 1st magnetic substance layer 1 and the 2nd magnetic layer 2 made of the thin film having a higher coercive force than that of the layer 1 and having the vertical anisotropy in the vertical direction of the film face is provided. A part of the recording medium is absorbed to the layer 1 by irradiating laser light from the base (a) of the recording medium, the light is transmitted through a part and absorbed in the layer 2 while being reached to the layer 2. Thus, the temperature of the layer 2 is increased and magnetization is inverted. 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, MnBi-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. Because of its high light transmittance, it had the disadvantage of requiring a high-output laser for recording. Among these, rare earth-transition metal amorphous systems are expected to compensate for the drawbacks 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, JP-A-55-65
As disclosed in Japanese Patent Application Laid-open No. 41 and JP-A-58-6542, by thinning the magnetic recording layer 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. -force, G
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 dCo or CdFe 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, an optimum bias magnetic field must be applied for recording.

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 following drawbacks:
SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium that can produce stable recording bits with a high reproduction signal level and, as a result, can perform high-density recording.

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 includes a transparent substrate, and one or more metal elements selected from transition metals and one or more metal elements selected from rare earth metals formed on the substrate. a first magnetic layer made of a thin film dispersed throughout the body and having magnetic anisotropy in a 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 in the direction perpendicular to the film surface.

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, glass, or the like. 1 is a first magnetic layer having an axis of easy magnetization perpendicular to the thickness direction in which one or more metallic elements of transition metals and one or more metallic elements of rare earth metals are dispersed in a dielectric material. For example, one or more metal elements selected from transition metals such as Fe, (:o, Ni, etc.) and Gd,
AIN contains one or more metal elements selected from rare earth metals such as Tb and Dy.

Si3N4, MgF2, BiF3, Si
It is configured by being dispersed in a dielectric material made of one or more selected from the group consisting of O, 5i02, TiO2, and Ta205.

The volume ratio (volume filling factor: q) of the transition metal and rare earth metal contained in the dielectric is preferably 0.5≦q≦0°85. 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 0.95, the magnetization will be affected by the atmosphere of oxygen, moisture, etc. This is because the magnetic layer becomes easily oxidized. Within this preferred range of volume filling ratio, it is preferable to set the film thickness and volume filling ratio 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 100 OA. As will be described later, the light absorption rate has a great influence on the recording and writing 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 above, each raw material constituting the first magnetic layer 1 is used as a multi-source vapor deposition source, and the sputtering method, ion plating method, etc. The 11a-type layer 1 can be formed by forming a film on the substrate by a TEINK method, an electron beam evaporation method, or the like.

2 is a second magnetic layer which has a higher coercive force than the 16111st magnetic layer 1 and exhibits magnetic anisotropy in the thickness direction;

A metal thin film made of a metal element of the 1st class -L arbitrarily selected from earth metals such as Tb and Dy, a barium ferrite tri film (BaFe204), a cobalt-chromium alloy thin film (C:o-Cr ), a manganese-bismuth alloy thin film (MnBi, Mr+C:uBi), and other magnetic thin films can be used.

A film is formed on the first magnetic layer 1 by a deposition method such as a sputtering method, an ion blasting method, an electron beam evaporation method, etc. using each of the raw material metals or ferrites constituting the magnetic thin film component as a multi-source deposition source. By this:5
Two magnetic layers 2 can be formed. The thickness of the second magnetic layer 2 varies depending on the material, but is usually preferably about 500.8 to 2000.8 cm.

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 1 of the magneto-optic recording medium shown in FIG. 1, and forming a protective layer 3 on the second magnetic layer 2. Ru. The antireflection layer is made of a dielectric material whose 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 anti-reflection layer is the first layer when laser light is incident on it.
By reducing reflected light from the surface of the magnetic layer, it functions to efficiently apply laser light to the magnetic layer.

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, plasma polymerization, etc. 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.

First, the recording and reproducing mechanism of the magneto-optical recording medium of the present invention is described.
The recording medium shown in the figure will be explained.

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 second magnetic layer 2, and is absorbed. Therefore, in the second magnetic layer 2, most of the optical energy is converted into thermal energy, and when the temperature of the second magnetic layer increases and reaches the Curie 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.

Part of the irradiated laser light is reflected by the first magnetic layer l, and part of it is transmitted and reflected by the second magnetic layer M2. A combination of these two reflected lights is detected during reproduction. The laser beam reflected by the first magnetic layer 1 is affected by the Kerr effect of this layer 1, and also passes through the fiiJ1m magnetic layer 1 to the second outer layer.
The laser beam reflected by the magnetic layer 2 is subjected to the Faraday effect of the first magnetic layer 1 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 may be reversed by the reproduction light, a configuration in which the reproduction light does not reach the second magnetic layer 2 is also possible. In this case, a material with a large Kerr rotation angle is used for the first magnetic Ml,
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 m-layer and a second magnetic layer has a stable structure without being affected by the bias magnetic field applied during recording. Recording bits can be formed and storage stability is also improved.

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

[Example 1] On a slide glass substrate of 78 x 26 mm and thickness lIIlml, the first m-type layer was prepared by adding a portion of gadolinium-terbium-iron (Gd, Tb, Fe,) into -silicon oxide (Sin). was deposited. This film is formed using a Gd-Tb alloy (composition Gd:T-b = 1) on a Fe target.
: l) It was carried out by a binary sputtering method using a composite target arranged with chips and a SiO target. The volume filling factor of Gd, Tb, and Fe contained in SiO is 0.90, and the film thickness is 280. At this time, the transmittance of the first magnetic layer at a wavelength of 8'30 nm is 40%. On this first magnetic layer, Tb20
A (FegoCOlo)so thin film was formed to a thickness of 600 Å as a second magnetic layer. This film formation was performed using a sputtering method. The coercive force is about 2.5 KOe. This magneto-optical recording medium was irradiated with a semiconductor laser beam with a wavelength of 830 nm and an output of 25 mW from the substrate side, and the Kerr rotation angle was measured with a magnetic field of 8 KOe applied perpendicular to the thickness direction. As a result, θ was ~1. 2° was obtained.

[Example 2] On a disk-shaped glass substrate with a diameter of 200 cm and a thickness of 1.5+o+w, a total of one magnetic layer,
A second magnetic layer was formed. After forming a SiO protective layer with a thickness of 400 OA on top of it using electron beam evaporation,
A magneto-optical recording medium was fabricated by bonding glass protective plates together using an adhesive.

This magneto-optical recording medium was irradiated with a laser beam from the substrate side for recording.The light source had an output of 25 mW and a wavelength of 8.
A bias magnetic field was applied in the thickness direction of the magnetic layer using a 30 nm semiconductor laser. While rotating this disc-shaped magneto-optical recording medium at 150 Orpm, the magnetic layer is uniformly magnetized, and the laser is pulsed to generate a frequency of 2 MH.
The signal of z was recorded in bits. The bias magnetic field applied at this time was 0.5 KOe. As a result of reproducing this using a semiconductor laser with an output of 10 mW, the recording frequency was 2.
At MHz, a reproduced signal of about 480 mV was obtained and had a good signal waveform. Also, the C/N at this time is band 30
4 e dB h<4 at KHz was obtained. Furthermore, as a result of recording while changing the bias magnetic field in the range of 0.4 to 0.7 KOe and microscopic observation of the recorded bits, it was found that the recorded bits remained stable even with changes in the bias magnetic field. It was confirmed that 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 95% R, H, and measuring the change in coercive force over the course of 1000 hours. It was found that the coercive force hardly decreased and the storage stability was superior to that of conventional magneto-optical recording media.

Further, as the first magnetic layer, one or more metal elements of Fe, Go, and Ni and one or more metal elements of Gd, Tb, and Oy are combined with AIN, Si3N4, MgF2. B
iF3. SiO,5i02. TiO2゜Ta205
Similar experiments were conducted on various magneto-optical recording media prepared by using the above-mentioned metal thin film or ferrite thin film as the second magnetic layer. , the reproduction signal level is high, and the stability of the recorded bits is almost unaffected by the bias magnetic field.
It was also found that storage stability was improved.

[Brief explanation of the drawing]

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...Antireflection layer l゛...11a layer 2...Second magnetic layer 3...Protective layer 4...Adhesive layer

Claims (1)

[Claims] A film surface consisting of a transparent substrate and a thin film formed on the substrate in which one or more metal elements selected from transition metals and one or more metal elements selected from 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. 1. A magneto-optical recording medium comprising at least a second magnetic layer having magnetic properties.