JPS6120244A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetooptical recording medium having a larger signal to noise ratio and excellent shelf life by forming the magnetic recording layer of a thin film dispersed with >=1 kind of transition metals and >=1 kind of metallic elements such as rare earth elements into a dielectric material and having the axis of easy magnetization perpendicular to the film plane and forming a reflective film on one side of the magnetic recording layer. CONSTITUTION:The magnetic recording layer is formed by dispersing the metallic elements of >=1 kind of transition metals such as Fe, Co and Ni or the metallic elements of >=1 kind of the rare earth metals such as Gd, Tb and Dy in >=1 kind of the dielectric materials selected from the group consisting of AlN, Si3N4, MgF2, BiF3, SiO, SiO2, TiO2 and Ta2O5. The volumetric packing of the rare earth or transition metals is preferably 50-95% by the volume of the magnetic recording layer. The optimum film thickness is usually 250-1,000Angstrom although said thickness varies with the kinds of the rare earth or transitio metals and the packing. The reflective film is preferably formed by using a material such as Au, Ag, Cu or Al to 300-800Angstrom film thickness and by a method such as an electron beam vapor deposition method.

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]

In recent years, with the development of computer technology, it has become necessary to process enormous amounts of information. One of the elemental technologies that support this information processing is high-density optical memory.

Currently, methods that have already been put into practical use include a method of irradiating a recording disk with laser light to form a focus, and a method of changing optical characteristics.

However, the above methods are limited to reproduction-only or additional recording, and there are few devices that can erase information and reproduce and record new information.

The present invention relates to a magneto-optical recording medium that is expected to be an element that can be erased and redeployed for recording information.

There are two methods for reproducing magneto-optical recording media: one using the Faraday effect and the other using the Kerr effect. Although magneto-optical recording media using these methods have the above-mentioned advantages, they also have the disadvantage of low reproduction signal levels, especially in the Kerr effect reproduction method, because the Kerr rotation angle is small.
It is difficult to find a way to increase the signal-to-noise ratio (S/N).

Therefore, in order to increase the Kerr rotation angle, studies have been conducted to improve the magnetic material and to form a dielectric thin film such as SiO or 5i02 on the recording medium to utilize multiple reflections on the surface of the magnetic layer. Furthermore, as disclosed in JP-A-55-8541 and JP-A-58-6542, by thinning the amorphous thin film and providing a metal reflective layer on the back surface,
A method of increasing the Kerr rotation angle using the Kerr effect and Faraday effect is also known. Alternatively, the Kerr rotation angle can be increased more efficiently by providing a transparent dielectric film thickness between the amorphous magnetic film layer and the reflective layer and optimally selecting the material and film thickness of each of the three layers. There is also a report that it can be done (J, Appl, Phys, Vol 53 pb
6 P, 4485-4484).

However, in these methods, the thickness of the amorphous magnetic film layer needs to be 250A or less in order to transmit the readout light, so if it is left in a high temperature and high humidity environment in the presence of oxygen, It is easily oxidized, resulting in a decrease in the recording sensitivity of the medium, an increase in errors during recording and reproduction, and signal deterioration.

[Object of the Invention] An object of the present invention is to improve the above-mentioned drawbacks and provide a magneto-optical recording medium having a larger signal-to-noise ratio (S/N) and excellent storage stability.

The objects of the present invention are achieved by the following magneto-optical recording medium.

[Configuration of IJ1] That is, the magneto-optic recording medium of the present invention has at least this magnetic recording layer on a substrate, and includes the following:
The magnetic recording layer is a thin film having an axis of easy magnetization perpendicular to the film surface in which one or more transition metals or one or more rare earth metals are dispersed in a dielectric material, and the magnetic recording layer is a thin film having an axis of easy magnetization perpendicular to the film surface. It is characterized by forming a film.

The magnetic recording layer of the magneto-optical recording medium of the present invention has Aj
lN, 5i3Ha + MgF2, BiF3
, SiO,5i02.

One or more metal elements of transition metals such as Fe, Go, Xi or Cd, Tb in one or more dielectrics selected from the group consisting of Ti07 and Ta205.
, Dy, etc., and has an easy axis of magnetization perpendicular to the film surface.

The volume filling factor of the rare earth or transition metal is preferably 50 to 95% with respect to the volume of the magnetic recording layer. If the volume filling factor q is 50% or less, magnetization with perpendicular magnetic anisotropy in the thickness direction It exists stably, and q is 95%.
This is because the magnetic layer is likely to be oxidized by atmospheres such as oxygen and moisture. Further, the thickness of the magnetic recording layer must be set so that light transmitted through the recording layer and reflected by the reflective film can be detected. The maximum film thickness varies depending on the type of rare earth or transition metal and the filling rate, but is usually 250 to 100 OA.

The magnetic recording layer is formed using the above materials by a method such as sputtering, resistance heating evaporation, electron beam evaporation, or ion blating.

The reflective film of the magneto-optical recording medium of the present invention includes Au, A
Using materials such as g, Cu, and A/, the film thickness is 300 to 80.
It is preferable that the film be formed by a method such as an electron beam evaporation method.

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

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of the present invention.

In the figure, a is a light-transmitting writing side substrate made of plastic, glass, or the like. 1 is a magnetic recording layer, 2 is a reflective layer, and 3 is a protective layer. The protective layer may be provided by a method such as coating with an organic polymer film, or may be provided by a method such as vapor deposition using an inorganic material such as butyride, nitride, or sulfide, or a metal material.

When a laser beam is irradiated from the substrate a side during reproduction.

A portion of this laser beam is reflected by the surface of the magnetic recording layer 1, and the remaining portion is transmitted through the magnetic recording layer 1 and reflected by the reflective layer 2. The former reflected light is subjected to the Kerr effect, and the latter reflected light is subjected to the Faraday effect. Therefore, the apparent Kerr rotation angle of the detection light for reproduction, which is a combination of these reflected lights, increases. As a result, the signal-to-noise ratio (S/N) obtained by irradiating the magneto-optical recording medium with laser light is improved.

Further, between the magnetic recording layer l of the present invention and the writing side substrate a,
Or SiO, 5i0 between the magnetic recording layer l and the reflective layer 2
By providing a dielectric layer such as No. 2, the Kerr rotation angle can be increased.

In addition, as shown in FIG. 2, the adhesive layer 4 is used to protect the protective substrate
′ may also be pasted together.

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

Next, specific examples of the magneto-optical recording medium according to the present invention will be described.

[Example 1] On a slide glass substrate of 76×2 Bmm and thickness l+s+s, a magnetic recording layer in which coherto co was dispersed in -silicon oxide (Sin) was formed. This was created by a binary ion blating method of SiO and co in plasma. G contained in SiO.

The volume fraction (q) of is q = 0.80, and the film thickness is approximately 450 people. Furthermore, a Cu reflective layer with a thickness of 400 Å was formed thereon using an electron beam evaporation method, and then a SiO protective layer with a thickness of 4000 Å was formed using an ion blasting method. This magneto-optical recording medium was irradiated with a He-He laser with a wave 1i of 33 nts and an output of 5 mW from the glass side, and the external magnetic field was changed using a 7 [magnet], and the hysteresis curve was measured, and the coercive force was approximately 3 KOe.
Met.

[Example 2] Direct? + 5iO was applied to a disc-shaped glass substrate of 200 mm and thickness 1.5+ using the same method as in Example 1.
-C:.

A magnetic recording layer was formed. G contained in SiO at this time
The volume ratio of o is q=o, e, and the film thickness is 450 people. On top of this, 11!2 thickness 4
A 20A Cu reflective layer was formed, and an S10 protective 3I layer with a thickness of 4000A was further formed by ion blating. A glass protective plate was attached to this using an adhesive to create a magneto-optical recording medium.

Recording and reproduction were performed on this magneto-optical recording medium using an optical head from the glass side. A He-Ne laser with an output of 30+sW was used as a light source, and a bias magnetic field was applied in a direction perpendicular to the surface of the magnetic recording layer. While rotating this disc-shaped magneto-optical recording medium at 1100 orp, the magnetic recording layer is uniformly magnetized, and a laser pulse is oscillated to obtain a 2M
The Hz signal was pit-recorded.

The bias magnetic field applied at this time was 1 KOe. When reproduction was carried out using a He--Ne laser with an output of 15 mW, a reproduction signal of about 100 .mu.V was obtained.

[Example 3] 5iO-G was deposited on a disk-shaped glass substrate with a diameter of 200 cm and a thickness of 1.5 cm using the same method as in Example 1.

A magnetic recording layer was formed. C contained in SiO at this time
The volume fraction of O is q = 0.65, and the film thickness is 400. Next, a SiO dielectric layer was deposited on this layer to a thickness of 400 Å using the ion blasting method, and a Cu reflective layer was further deposited to a thickness of 400 Å using the electron beam evaporation method. A SiO protective layer having a thickness of 4,000 Å was formed using the ion blating method, and a glass protective plate was bonded to the SiO protective layer to prepare a magneto-optical recording medium. Recording and reproduction were performed on this recording medium in the same manner as in Example 2. As a result, a reproduced signal of approximately 150 V was obtained at a recording frequency of 2 MHz.

Next, this magneto-optical recording medium was placed at a temperature of 45°C and a humidity of 95%.
A storage stability test was conducted by leaving the sample in an R, H, atmosphere and measuring the change in coercive force over time. The results are shown in Figure 3.

Figure 3 shows the initial coercive force (coercive force) 1c for lea
The change in is expressed as Hc/Hco.

In addition, magneto-optical recording media made of conventional GdTbFe amorphous thin films were prepared by changing conditions such as the composition of GdTbFe and film thickness, and storage stability tests were conducted in the same manner as in Example 2. As a result, curves as shown in FIG. 3 were obtained in all cases.

As is clear from the examples described above, in the conventional magneto-optical recording medium made of an amorphous thin film, the coercive force decreases significantly over time, whereas in the magneto-optic recording medium according to the present invention, the coercive force decreases significantly over time. It can be seen that there is very little decrease in coercive force caused by oxidation, and that the storage stability is excellent.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views of an embodiment of a magneto-optical recording medium according to the present invention. FIG. 3 is a diagram showing the results of storage stability tests of Examples and Comparative Examples of the present invention. a--Writing side substrate a'-m-Protective substrate 1-m-Magnetic recording layer? -m-Reflection layer 3--Protective layer 4--Adhesive layer Fig. 1 Fig. 2

Claims (1)

[Claims] In a magneto-optical recording medium having at least a magnetic recording layer on a substrate, the magnetic recording layer has an axis of easy magnetization perpendicular to the film plane in which one or more transition metals or one or more rare earth metals are dispersed in a dielectric material. 1. A magneto-optical recording medium, characterized in that the magnetic recording layer is a thin film having a reflective film formed on one side of the magnetic recording layer.