JPS63317947A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide thermal stability to a magneto-optical recording medium consisting of an amorphous magnetic film having an axis of easy magnetization in a perpendicular direction and to decrease the deterioration thereof with lapse of time by subjecting the magnetic film of said recording medium to a heat treatment at and for a specific ambient temp. and time. CONSTITUTION:This magneto-optical recording medium is constituted by forming an Si3N4 film 2, a recording film 3, an Si3N4 film 4 successively on a PC substrate 1. A Tb21Fe72CO7 film or the like is used as the recording film 3 and is subjected to the heat treatment for 2-0.5hr at 70-90 deg.C. The coercive force attains the satd. value in 2hr, 1hr and 30min, respectively, when the film is subjected to the heat treatment at, for example, 70, 80, 90 deg.C. The length of recording pits does not change and the stable pit length is obtd. even when the same tracks of such medium are subjected to cycles of recording and erasing by laser light. Cracks are generated in the protective film if the film is treated at 100 deg.C. The thermally stable magneto-optical recording medium is thus obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to magneto-optical recording in which recording and erasing is performed by changing the direction of perpendicular magnetization of an amorphous perpendicularly magnetized film using light beam irradiation and a bias magnetic field. It is related to the manufacturing method of the media.

[Conventional technology]

Conventionally, as a recording layer of a magneto-optical recording medium, an amorphous alloy thin film of an element selected from a group of heavy rare earth elements such as Gd, Tb, and Dy and a group of transition elements such as Fe and Co has been used. Specifically, TbFe, TbFeCo, Gd
Composition systems such as TbFe, GdTbFeCo, and TbDyFeCo are well known. In addition, for the purpose of teaching various physical properties, light rare earth elements such as Pr, Nd, Sm,
Transition metal elements such as Ti, Cr, Cu, or B, S
A metalloid element such as i may also be added. These recording layers are deposited directly on a disc-shaped transparent substrate made of glass, polycarbonate (PC), polymethyl methacrylate (PMMA), epoxy resin, etc.
A film is generally formed by sputtering via a dielectric layer such as 'NJ or AρN5SiO. Usually, a dielectric or metal protective layer is provided on the recording film to prevent the recording film from oxidizing. The recording layer of the recording medium produced in this manner is generally used as it is without any special heat treatment.

[Problem that the invention seeks to solve]

However, an amorphous film made by sputtering or the like has a thermally unstable structure. Therefore, if it remains red for a long time, its structure changes. Furthermore, it is expected that the amorphous structure will gradually change by repeating single-point recording and erasing many times, or by repeating reproduction by laser beam irradiation. On the other hand, the magnetism of a magnetic thin film largely depends on its structure. In particular, the Curie temperature and coercive force are quantities that play a fundamental role in the recording mechanism of magneto-optical recording, so changes in magnetism caused by changes in structure are fatal to magneto-optical recording and reproducing characteristics. This will have a negative impact. For example, it is known that recording sensitivity is generally determined by the Curie temperature and coercive force at high temperatures, but when recording sensitivity changes due to changes in physical property values, the recording pit length also changes. It is easy to imagine that the above-mentioned changes do not have a large effect on data reliability, especially in the length recording method where pit length is used as information.

As described above, conventional magneto-optical recording media have problems caused by instability of the structure of the recording film. That is, due to the thermal cycle given to the recording film by repeating recording, erasing, and reproducing, a change in the structure accompanied by a change in the magnetism of the recording film occurs, and the recording and recording of the magneto-optical recording medium.
It has defects that affect the reproduction characteristics and, ultimately, the reliability of recorded data. The present invention is intended to solve these problems, and its purpose is to provide a thermally stable amorphous magneto-optical recording film and provide a highly reliable magneto-optical recording medium. be.

[Failure to solve the problem]

The method for manufacturing a magneto-optical recording medium of the present invention includes the step of manufacturing a magneto-optical recording medium in which the recording film is an amorphous magnetic film having an axis of easy magnetization perpendicular to the film surface.
It is characterized by performing heat treatment at a temperature of 0° C. for 30 minutes to 2 hours.

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples. 1st
The figure schematically shows the structure of the magneto-optical recording medium used in this example. Sis with a film thickness of 90 nm is placed on a PC board 1 with a diameter of 120 mm and a thickness of 1.2 mm with a guide groove.
Na film 2.1100n recording film 3.90nm 5is
Na film 4 was formed in order.

When a magneto-optical recording medium using a sputtered film with the composition Tbz + Few * CO7 as the recording film was kept in a constant temperature bath at 70°C, the coercive force at room temperature was plotted against the time it was held at 70°C. The object is shown in Figure 2. It can be seen that the coercive force decreases with time and reaches saturation in about 2 hours at 70°C.

Then, on the same track of the media treated for 2 hours at 70°C,
Erasing/recording cycles were performed using a laser beam of mW. In Figure 3, the horizontal axis shows the number of erasing/recording circles, and the vertical axis shows the pit length change (%) with respect to the first recording pit length (0>).Also, the same medium without heat treatment is shown. The changes in the recorded pit length are also shown in (m).As is clear from Figure 3, the recorded pit length changes until about 103 erasing and recordings are repeated in the case without heat treatment, whereas the record pit length changes in the case without heat treatment. The treated medium can have a stable pit length.

Next, similar effects were investigated by changing the heat treatment temperature and heat treatment time. Table 1 shows the temperature of the heat treatment applied to the same sample as described above and the time at which the change in coercive force was saturated.

In Table 1, sample 5 could not be used for the erasing/recording repetition test because cracks occurred in the protective film during heat treatment. In addition, sample 1 requires heat treatment for 4 hours or more and is therefore not economically viable. Therefore, we conducted repeated erasing and recording tests at a heat treatment temperature of 70°C, 180°C, and 190°C by changing the heat treatment time, and the change in recorded pit length was reduced to 0 by processing for 2 hours, 1 hour, and 30 minutes, respectively. I was able to do that. The processing time at each temperature was 2 hours and 1 hour, respectively.
If the time is less than 30 minutes, 100 to 1000 times.
It became constant after 1 cycle.

Similarly, recording films such as DyFeCo, GdTbFe, and Nd
The same results as the TbFeCo film were also obtained when a film such as TbFeCo was used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a thermally stable amorphous magneto-optical recording film and provide a highly reliable magneto-optical recording medium.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a magneto-optical recording medium used in an example of the present invention. 1... PC board 2.4... S i3 Na film 3... Recording film FIG. 2 is a diagram showing the relationship between the heat treatment time at 70° C. and the coercive force of the recording film. FIG. 3 is a diagram showing the relationship between the number of erasing/recording cycles and the change in recording pit length. Note that 0) is a material that has been heat-treated at 70°C for 2 hours, and (M) is a material that has not been heat-treated. Applicant: Seiko Epson Corporation Figure 1-2

Claims (1)

[Claims] In the process of manufacturing a magneto-optical recording medium whose recording film is an amorphous magnetic film with an axis of easy magnetization perpendicular to the film surface, the recording film is heat treated at a temperature of 70°C to 90°C for 30 minutes to 2 hours. A method for manufacturing a magneto-optical recording medium, characterized by: