JPH0573973A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the magneto-optical recording medium which has excellent repeating durability of erasing/recording/reproducing and has a recording sensitivity over an adequate range. CONSTITUTION:The Curie temp. of the magneto-optical recording layer in the magneto-optical recording medium constituted by laminating a 1st dielectric layer, a magneto-optical recording layer, a 2nd dielectric layer, and a reflection layer on a substrate is in a 160 to 220 deg.C range and the film thickness of the 2nd dielectric layer is in a 10 to 30nm range. The problem of the conventional media that the recording sensitivity deteriorates if the repeating durability of the erasing/recording/reproducing is attempted to be improved is solved. The magneto-optical recording medium with which the excellent repeating durability and the recording sensitivity of the adequate range are made compatible is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium having excellent durability against repeated erasing / recording / reproduction.

[0002]

2. Description of the Related Art Optical disks are large-capacity / high-density external storage devices, and their importance is increasing year by year. Above all,
Magneto-optical recording has attracted particular attention as a rewritable nonvolatile external storage system. The magneto-optical recording method is one in which recording is performed by an external magnetic field, and the property that the magnetization is directed in the direction of the external magnetic field to which only a minute portion of the magneto-optical recording film heated by laser light is applied is It is the principle of erasure. Therefore, it is indispensable to study the thermal behavior when the magneto-optical recording medium is irradiated with laser light in order to develop a magneto-optical disk.

It is known that in a magneto-optical disk, the reproduction signal strength gradually decreases when erasing / recording / reproduction is repeated.

This deterioration is considered to be due to structural relaxation of the amorphous magneto-optical recording layer. Usually, the structural relaxation of the amorphous material is a thermal activation process, so if the film structure in which heat is hard to stay in the magneto-optical recording layer is realized, the maximum temperature reached in the magneto-optical recording layer can be suppressed to a low level.
It is considered that the structural relaxation of the amorphous structure can be suppressed.

As an example of such a magneto-optical recording medium,
A first dielectric layer, a magneto-optical recording film, and a second dielectric layer on the disk substrate.
A magneto-optical disk having a four-layer structure, which is formed by sequentially laminating a dielectric layer and a reflective layer, is disclosed in, for example, Japanese Patent Laid-Open No. 152520/1990.
No., etc.

However, the fact that heat is hard to stay in the magneto-optical recording layer means that the heat easily escapes from the magneto-optical recording layer. This means that a large laser light output is required for recording / erasing, which means that the recording sensitivity becomes poor. In the above-mentioned prior art, no consideration is given to such deterioration in recording sensitivity accompanying improvement in repeated durability.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to have excellent durability against repeated erasing / recording / reproduction, and
An object is to provide a magneto-optical recording medium having a recording sensitivity in an appropriate range.

[0008]

In order to solve the above problems, the present invention provides an optical system in which a first dielectric layer, a magneto-optical recording layer, a second dielectric layer and a reflective layer are laminated on a transparent substrate. In the magnetic recording medium, the Curie temperature of the magneto-optical recording layer is 160.
Provided is a magneto-optical recording medium characterized by being in the range of 220 ° C to 220 ° C and having a film thickness of the second dielectric layer in the range of 10 to 30 nm.

The substrate used in the present invention is, for example,
Examples thereof include substrates such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin in which guide grooves are directly formed in resin or glass, substrates in which guide grooves are formed on a flat plate of glass or resin by a photopolymer method, and the like.

An inorganic dielectric having a high transparency is used for the dielectric layer. Examples of the material include SiN _x and Si
O _x , AlSiON, AlSiN, AlN, AlTi
N, Ta ₂ O ₅ , ZnS and the like can be mentioned, but among them, S
iN _x is preferred. The refractive index of these dielectric layers is 1.8 to
A range of 2.5 is preferred.

Examples of the material forming the magneto-optical recording layer include TbFeCo and NdDyFeCo.
Examples include alloys of transition metals and rare earth metals.

As the material of the reflective layer used in the present invention,
Examples include Al and alloys of Al with other metals.
1, Al-Ti alloy, and Al-Cr alloy are preferable.

The dielectric layer, the magneto-optical recording layer, and the reflective layer are
Physical vapor deposition (PVD) such as sputtering and ion plating, chemical vapor deposition (CV) such as plasma CVD
D) or the like.

The magneto-optical recording medium thus formed may be used alone or may be used by adhering two so that the substrates are on the outside.

[0015]

The present invention improves durability against repeated erasing / recording / reproduction by adopting a film structure in which heat easily escapes from the magneto-optical recording layer, and at the same time, the deterioration of recording sensitivity caused at that time is prevented by the magneto-optical recording. By preventing it by adjusting the Curie temperature of the recording layer, it is possible to achieve both excellent repeat durability and appropriate recording sensitivity.

In magneto-optical recording, first, heat is applied to the magneto-optical recording medium by laser light irradiation. The heat generated by raising the temperature of the magneto-optical recording layer is conductively transmitted in the magneto-optical recording layer, or after being transmitted to the reflective layer through the second dielectric layer, it is conductive in the reflective layer or in the atmosphere. It radiates into the interior and escapes to the area other than the laser light irradiation area. Considering the heat transmitted to the reflective layer through the second dielectric layer, the thermal conductivity of the dielectric layer is smaller than that of the other layers, and thus the thinner the second dielectric layer, The heat flowing to the reflecting layer increases, and the heat escaping from the magneto-optical recording layer also increases. However, since the second dielectric layer also plays the role of a protective film for the magneto-optical recording layer, if the film thickness is made too small, the magneto-optical recording layer is easily oxidized and the recording characteristics deteriorate. I will end up. Therefore, there is an appropriate range for the film thickness of the second dielectric layer, and 10 to 30 nm is the appropriate film thickness range.

As the Curie temperature of the magneto-optical recording layer is lower, recording / erasing can be performed with a smaller laser light output, that is, the recording sensitivity is better. However, if the Curie temperature is too low, the Kerr rotation angle at room temperature becomes small, and the reproduction signal strength is reduced. Therefore, there is an appropriate range for the Curie temperature, which is 160 to 220 ° C.

[0018]

EXAMPLES A concrete description will be given below with reference to examples.

(Embodiment 1) FIG. 1 is a sectional view of an example of the magneto-optical recording medium of the present invention. A magneto-optical recording medium having this structure was manufactured by the following procedure.

A polycarbonate substrate 1 having a guide groove and a diameter of 5.25 inches is formed on a substrate 1 made of SiN _x.
The first dielectric layer 2 having a thickness of 00 nm is formed by the RF sputtering method, and the magneto-optical recording layer 3 having a thickness of 25 nm made of Tb ₂₀ Fe ₇₂ Co _{8 is} formed on the first dielectric layer 2 by the DC sputtering method. S
A second dielectric layer 4 made of iN _x and having a thickness of 20 nm was formed by RF sputtering, and a reflective layer 5 made of AlTi alloy and having a thickness of 75 nm was formed by DC sputtering on the second dielectric layer 4.

As a result of magnetic measurement of the magneto-optical recording medium thus formed, the Curie temperature was 200 ° C.

(Comparative Example 1) As a comparative example, a magneto-optical recording medium having the same structure as that of Example 1 was manufactured by the following procedure.

First, a polycarbonate substrate 1 having a guide groove and a diameter of 5.25 inches is formed on a substrate 1 made of SiN _x.
The first dielectric layer 2 having a thickness of 00 nm is formed by the RF sputtering method, and the magneto-optical recording layer 3 having a thickness of 25 nm made of Tb ₂₀ Fe ₆₉ Co _{11 is} formed on the first dielectric layer 2 by the DC sputtering method. S
A second dielectric layer 4 made of iN _x and having a thickness of 20 nm was formed by RF sputtering, and a reflective layer 5 made of AlTi alloy and having a thickness of 50 nm was formed thereon by DC sputtering.

As a result of magnetic measurement of the magneto-optical recording medium thus formed, the Curie temperature was 230 ° C.

(Evaluation) With respect to the magneto-optical recording media obtained in Examples and Comparative Examples, the dependence of CNR (Carrier to noise ratio) on laser light output at a rotation speed of 1,800 rpm and a radius of 30 mm was measured. Also, all the magneto-optical recording media of Comparative Example 1 showed the maximum CNR value (about 49 dB) when the laser light output was 5.5 mW. From this result,
It was found that the recording sensitivities of both media were almost the same.

Next, these magneto-optical recording media were attached to a magneto-optical disk drive, and a repeated erasing / recording / reproducing durability test was performed on the same track at a rotation speed of 2400 rpm. The relationship between the number of repetitions and the CNR reduction amount in this test is shown in FIG. These results show that the magneto-optical recording medium according to the present invention has excellent erasing / recording / reproducing repetition durability.

The same effect was obtained by using Al or Al-Cr alloy other than Al-Ti alloy for the reflective layer.

[0028]

The magneto-optical recording medium according to the present invention has a suitable recording sensitivity. Therefore, according to the present invention, it is possible to improve the repeating durability of the magneto-optical disk without requiring new improvements on the device side such as an optical disk drive.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a magneto-optical recording medium illustrated in Examples and Comparative Examples of the present invention.

FIG. 2 shows the magneto-optical recording medium illustrated in Examples and Comparative Examples of the present invention, which is attached to a magneto-optical disk drive and erased / recorded / recorded on / from the same track at a rotation speed of 2400 rpm.
Number of repetitions and CNR in repeated durability test of regeneration
It is a chart showing the relationship with the amount of decrease.

[Explanation of symbols]

 1 substrate 2 first dielectric layer 3 magneto-optical recording layer 4 second dielectric layer 5 reflective layer

Claims (3)

[Claims] 1. In a magneto-optical recording medium in which a first dielectric layer, a magneto-optical recording layer, a second dielectric layer and a reflective layer are laminated on a transparent substrate, the Curie temperature of the magneto-optical recording layer is 16.
A magneto-optical recording medium characterized in that it is in the range of 0 to 220 ° C. and the film thickness of the second dielectric layer is in the range of 10 to 30 nm. 2. The reflective layer comprises Al, Al--Ti alloy and A.
The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium comprises a substance selected from the group consisting of l-Cr alloys. 3. The first dielectric layer and the second dielectric layer are SiN
_The magneto-optical recording medium according to claim 2, wherein the magneto-optical recording medium comprises _x .