JPH01107343A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the generation of the shape defect of a recording domain and to obtain high C/N ratio (signal to noise ratio) by specifying the thickness of a recording film. CONSTITUTION:A silicon nitride film (dielectric film) 2 is laminated by a magne tron high-frequency sputtering method on a transparent resin substrate 1 and a GdTbFeCo film (recording film) 3 is laminated thereon as the recording film by the similar method. The thickness of the recording film 3 is adjusted to >=400Angstrom and <=600Angstrom . Large coercive force of >=6kOe is easily obtd. at room temp. if the recording film 3 is formed to <=600Angstrom thickness. The coercive force of the recording domain subjected to heating up and writing by irradiation of laser light is then sharply increased in the process of being rapidly cooled down to room temp., by which the movement of magnetic walls is prevented. The increase in the noise level of the magneto-optical disk is thereby prevented and the high C/N ratio is obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magneto-optical recording medium that performs recording, reproduction, and erasing by irradiation with laser light, and particularly relates to a magneto-optical recording medium suitable for obtaining particularly good recording and reproduction characteristics. Regarding recording media.

[Conventional technology]

As a recording film of a magneto-optical recording medium, G d T b Fe Co , G d T b
Fe.

DyTbFeCo, NdTbFeCo.

Examples of using rare earth/transition metal amorphous films containing two or more types of rare earth elements such as NdDyFeCo are described in JP-A-58-196639 and JP-A-60-83305. The characteristics of these recording films are that of conventional TbF
The second rare earth element is added to e, TbFsCo, and DyFeCo to increase the Kerr rotation angle that determines the magnitude of the reproduced signal.

The structure of a magneto-optical disk used in practice is such that a dielectric film, a recording film, and a protective film are laminated in this order on a disk substrate. In this case, the thickness of the recording film is approximately 10
It is set to 00 people. This means that the thickness of the recording film is 10
This is because when the thickness is 00 Å or more, the magnetic properties of the recording film have little dependence on the film thickness, and the magnetic properties can be easily controlled. Furthermore, if the thickness of the recording film is made thicker than necessary, the recording sensitivity will be significantly reduced.

On the other hand, another structure of the magneto-optical disk is a structure in which a first dielectric film, a recording film, a second dielectric film, and a reflective film are laminated in this order on a disk substrate. In this configuration, since the reproduction laser beam needs to pass through the recording film, the thickness of the recording film cannot be made more than 250 Å.An example of the second configuration is the Journal of the Japan Society of Applied Magnetics, Vol. It is described in Page (1987).

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the fact that the addition of the second rare earth element causes shape defects in the recording domain, and there is a problem that a high C/N ratio (signal-to-noise ratio) cannot be obtained. Ta.

That is, T b Fe and TbFeCo*DyFaC
o The shape of the recording domain written by irradiating the recording film with laser light is circular or oval, whereas G d
T b F e Co and G @ T b F e vD
y T b F e Co , G d D y F
eCo.

When domains are recorded on a recording film such as NdTbFeCo or NdDyFeCo, the contours of the domains are disturbed or the sizes of the domains are irregular. Such a defective shape of the recording domain causes an increase in the noise level and causes a decrease in the C/N ratio.

Further, in a magneto-optical disk having a structure having a reflective film, there is a problem that the number of laminated layers increases, which complicates the manufacturing process and increases costs.

An object of the present invention is to provide a magneto-optical recording medium with a simple laminated structure that is suitable for preventing the occurrence of defective shapes of recording domains and obtaining a high C/N ratio in a high Kerr rotation angle recording film. It is in.

[Means for solving problems]

The above object is achieved in a magneto-optical recording medium constructed by laminating a dielectric film, a recording film, and a protective film in this order on a transparent substrate, by setting the thickness of the recording film to 400 Å or more and 600 Å or less. .

[Effect]

By reducing the thickness of the recording film to 600 Å or less.

G d T b F e Co or G d T b F
e.

D y T b F e Co , N d T b
F e Co .

Even in NdDyFeCo, GdDyFeCo, etc., a large coercive force of 6 k Oe or more can be easily obtained at room temperature. Therefore, the coercive force of the recording domain written by temperature rise due to laser beam irradiation increases rapidly during the process of rapid cooling to room temperature, and movement of the domain wall can be prevented. Also, the thickness of the recording film is 6
When the thickness is less than 00 Å, the recording film is rapidly heated and cooled by laser beam irradiation. Due to this rapid increase in coercive force and rapid heating and cooling of the recording film, the shape of the recording domain becomes circular or oval, reflecting the temperature distribution of the area heated by laser beam irradiation, resulting in irregular contours and large Does not cause unevenness.

On the other hand, if the thickness of the recording film is made smaller than 400, the amount of laser light transmitted through the recording film will increase, the reproduction signal level will drop, and a high C/N ratio cannot be obtained.

〔Example〕

Examples of the present invention will be described in detail below.

A magneto-optical disk having the configuration shown in FIG. 1 was manufactured.

85 silicon nitride films (dielectric films) 2 are formed on a transparent resin substrate 1 with a diameter of 13 cm by magnetron high frequency sputtering.
G d T b Fe Co
A film (recording film) 3 was laminated. The sputtering gas was pure Ar gas, and the high frequency output was 1.5 kW. The thickness of the GdTbFeCo film was varied from 200 to 1200 by adjusting the sputtering time. Further, 1,500 silicon nitride films (protective films) 4 were laminated as a protective film.

FIG. 2 shows the recording and reproducing characteristics of the above-mentioned disks manufactured by changing the thickness of the recording film with respect to the thickness of the recording film. The composition of each recording film was gdisTtz+Feseco7CfM%). The recording and reproducing conditions are: recording laser output cuff mW, recording magnetic field 4
000 e, recording frequency I MHz, disk rotation speed 180 Or p m + reproduction laser output 1.5 m
It is W.

As shown in Figure 2, the noise level is determined by increasing the thickness of the recording film by 6
By lowering it to 00 Å or less, it was reduced to -60 dBm. On the other hand, when the thickness of the recording film is reduced, the carrier level increases because the recording sensitivity of the disc increases, but at 400
If you make it smaller than a person, it will decrease rapidly. This is mainly because the transmitted component of the laser beam increases and the amount of reflected light decreases.

6 when the thickness of the recording film is in the range of 400 Å or more and 600 Å or less
A high C/N ratio of 0 dB or more was obtained.

FIG. 3 shows the coercive force and reflectance of the above-mentioned disk with respect to the thickness of the recording film. The coercive force increases as the thickness of the recording film becomes thinner, and was 10 k Oe or more at 600 Å or less. The reflectance decreased rapidly when the film thickness became less than 400 mm.

Figure 4 shows that the thickness of the recording film is 600mm and 1000mm.
Showing the shape of the recording domain for a human disk, 6
00 people's disc had a circular recording domain, but
In the disk of 1000 people.

Unevenness occurred in the contour of the recording domain. Also, in a disk with 1000 people, the size of the recording domain is not constant, and 0.
The width varied from 6 μm to 0.9 μIn. It is thought that such disturbances in the contours and irregularities in size of the recording domains are the cause of the increase in the noise level. on the other hand,
In a magneto-optical disk using a T b Fe Co film as a recording film, even when the film thickness was 1000 Å or more, the recording domain was circular or oval, had no disturbance in outline, and had a constant size. Further, almost no increase in noise level due to increase in film thickness as shown in FIG. 2 was observed.

In FIG. 5, G d T b Fe Co is used as a recording film.
.

G d T b F e , D y T b F e
Co.

The C/N ratio obtained in a magneto-optical disk using N d T b Fe Co is shown with respect to the film thickness of the recording film.

The recording and reproducing conditions are the same as those described above. The composition of each recording film is Cdz8TbeFeaeCo7tGdzo.
TbzISF8711. DyzaTbaFeeacog
.

NdeTbzaFeesco7 (atomic %). In any case, the thickness of the recording film is 400 Å or more,
A high C/N ratio was obtained in the range of 600 Å or less.

In this example, we have only described the case of a recording film that combines rare earth elements and transition metals, but other elements such as AQ, Ti1Pt*Nb, P, and B are added to this for the purpose of improving corrosion resistance. A similar effect can be obtained with a recording film made by using the same method.

Further, the dielectric film or the protective film is not necessarily a silicon nitride film, and other conductive films such as a silicon oxide film or a zinc sulfide film may also be used. Furthermore, it is also possible to use a protective film with a multilayer structure, such as a combination of a metal film and a dielectric film.

Furthermore, in the above embodiments, the recording and reproducing characteristics were described when magneto-optical recording was performed using an optical modulation method, but the same was true for magneto-optical recording using a magnetic field modulation method. That is,
±300 while irradiating the recording film with 6 mW continuous laser light.
When a high frequency magnetic field of 0 e was applied, a C/N similar to that shown in FIG. 5 was obtained.

〔Effect of the invention〕

According to the present invention, it is possible to prevent an increase in the noise level of the magneto-optical disk, so there is an effect that a high C/N ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a part of a magneto-optical disk according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a part of a magneto-optical disk according to an embodiment of the present invention. A diagram showing the relationship between recording film thickness and reproduction output, Figure 3 is G.
d T b A diagram showing the relationship between the film thickness, coercive force, and reflectance of the FeCo recording film, FIG. 4 is a diagram showing the shape of the recording domain of the GdTbFeCo recording film, and FIG. FIG. 3 is a diagram showing the relationship between the film thickness of a recording film and the C/N ratio of a magneto-optical disk. 1... Transparent substrate, 2... Dielectric film, 3... Recording film, 4... Protective film. No. 1, No. 2, 3°゛Discipline 4...I brutality 11 times Gct Tb Fe Co R14-(, #) Reporter U
Han's smell 4 (pe)

Claims (1)

[Claims] 1. In a magneto-optical recording medium constructed by laminating a dielectric film, a recording film, and a protective film in this order on a transparent substrate, the thickness of the recording film is set to be 400 Å or more and 600 Å or less. Features of magneto-optical recording media. 2. In claim 1, the recording film includes a rare earth element containing at least two or more kinds of rare earth elements.
A magneto-optical recording medium characterized by using an amorphous film mainly composed of transition metals. 3. In claim 2, the rare earth
A magneto-optical recording medium characterized in that the amorphous film mainly composed of a transition metal is a film mainly composed of any one of GdTbFeCo, GdTbFe, DyTbFeCo, GdDyFeCo, NdTbFeCo, and NdDyFeCo.