JPH02156447A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To execute overwriting by the magneto-optical disk using an optical modulation system by using an auxiliary film which is larger in saturation magnetization and coercive force than an information film and is higher in Curie temp. as well than the information film. CONSTITUTION:Polycarbonate is used for a substrate 1, TbFeCo for the information film 3, a GdCo film for the auxiliary film 4 and an SiN film for a protective film 2. The information film 3 having the small coercive force simultaneously directs the magnetization in the same direction when the magnetization of the auxiliary film 4 is first directed by an external strong magnet. Recording is then executed by a weak laser power Pl or strong laser power Ph. The external magnetic field H is applied at all times on the film 4 in the direction reverse from the magnetization direction of the film 4 at the time of the recording and the magnitude of the magnetic field Ho is set smaller than the coercive force of the film 4. The magnetization of the film 3 is directed to the magnetization direction of the film 4 in case of the power Pl and the magnetization of the film 3 is directed to the direction of the magnetic field Ho in case of the power Ph. Namely, the magnetization direction of the film 3 can be inverted by only the various intensities of the power and, therefore, the overwriting is possible regardless of the recorded information.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk, and particularly to an overridable magneto-optical disk.

[Conventional technology]

Conventional magneto-optical disks deposit an information film made of a perpendicularly magnetized film that exhibits the magneto-optic effect on a transparent substrate, and heat this information film with a laser beam to raise its temperature and reduce its coercive force. By the way, information is recorded by reversing the direction of magnetization using an external magnetic field.

For this reason, in conventional magneto-optical disks using information films, override has been performed using a magnetic field modulation method.

[Problem to be solved by the invention]

However, the above-mentioned magneto-optical disk,
Since the magnetic field modulation method is used, it is necessary to reverse the direction of the magnetic field at a high frequency, so the recording frequency is limited to about 5 MHz, and in order to apply a strong magnetic field to the medium surface,
Since it is necessary for the magnetic field generating part to be as close to the film as possible, there is a drawback that it cannot be used for bonded products.

[Means to solve the problem]

The magneto-optical disk of the present invention includes an information film and an auxiliary film formed on a substrate using a perpendicular magnetization film to enable overriding of the information film formed of a perpendicular magnetization film for recording information. The auxiliary film is stacked so that the saturation magnetization and coercive force of the auxiliary film are larger than that of the information film, and the Curie temperature of the auxiliary film is higher than that of the information film.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view schematically showing an embodiment of the present invention.

The magneto-optical disk shown in FIG. 1 includes a substrate 1, a protective film 2, an information film 3, and an auxiliary film 4.

The substrate 1 is made of polycarbonate (hereinafter referred to as PC), the information film 3 is made of TbFeCo, the auxiliary film 4 is made of GdCo, and a protective film 2 is used to prevent the information film 3 and the auxiliary film 4 from being oxidized.
A SiN film was used.

First, a SiN film with a film thickness of 800 nm was deposited as a protective film 2 on a substrate 1 made of polycarbonate by magnetron sputtering.
People piled up.

Next, 1,300 perpendicularly magnetized films made of a TbFeCo film were deposited thereon as a memory film 3, and 400 perpendicularly magnetized films made of a GdCo film were further deposited thereon as an auxiliary film 4. Finally, 800 SiN films were deposited as the protective film 2. The GdCo film constituting the auxiliary film 4 has a composition that has a compensation point above room temperature.

Figure 2 shows the temperature dependence of the coercive force and saturation magnetization of the auxiliary film 4 shown in Figure 1. Since the auxiliary film 4 is a ferrimagnetic film, the coercive force is maximum and the saturation magnetization is minimum at the compensation temperature. I can see it happening. That is, as the temperature increases, the compensation point approaches, so even if the saturation magnetization decreases, the coercive force does not decrease.

Next, with reference to FIG. 3, an override operation using the optical modulation method using the magneto-optical disk shown in FIG. 1 will be described.

First, the magnetization of the auxiliary film 4 is directed in one direction using an external strong magnet.

At this time, the information film 3 having a small coercive force is also magnetized in the same direction at the same time.

Next, recording is performed with a weak laser power Pl or a strong laser power Ph.

During recording with this laser, an external magnetic field Ho is always applied in a direction opposite to the magnetization direction of the auxiliary film 4.

At this time, the magnitude of the external magnetic field Ho is set smaller than the coercive force of the auxiliary film 4.

■ When recording with a weak laser power Since the laser power Pi7 is weak, only the information film 3 reaches the Curie temperature.

For this reason, the holding power of the information film 3 during the temperature rising process is lost,
During the cooling process, the information film 3 is pulled in the direction of magnetization of the auxiliary film 4.
The magnetization of the auxiliary film 4 is oriented in the same direction as the magnetization of the auxiliary film 4.

(2) When recording with strong laser power If the laser power PIl is strong, the temperature of the auxiliary film 4 rises at the same time as the information film 3 reaches the Curie temperature, and the saturation magnetization of the auxiliary film 4 decreases.

Therefore, during the cooling process, the magnetization of the information film 3 is dragged by the external magnetic field Ho and points in the direction of the external magnetic field HO.

However, at this time, even if the temperature of the auxiliary film 4 increases, the coercive force of the auxiliary film 4 must not become smaller than the external magnetic field HO, and the magnetization direction of the auxiliary film 4 must not be reversed.

In this way, when the laser power P1 is weak, the magnetization of the information film 3 is oriented in the direction of the magnetization of the auxiliary film 4, and when the laser power ph is strong, the magnetization of the information film 3 is oriented in the direction of the external magnetic field Ho.

In other words, since the magnetization direction of the information film 3 can be reversed just by changing the intensity of the laser power, override can be achieved regardless of the recorded information.

When this magneto-optical disk was used for recording and reproducing at a frequency of 1 to 10 MHz and a recording power of 5 to 10 MHz, it was found that overriding was possible.

〔Effect of the invention〕

The magneto-optical disk of the present invention has the advantage that by using an auxiliary film, override can be performed using an optical modulation method.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing one embodiment of the present invention, and FIG.
The figure shows GdC used in the auxiliary film shown in Figure 1. FIG. 3 is a graph showing the relationship between coercive force and saturation magnetization with respect to film temperature, and is a schematic diagram for explaining the override operation by the optical modulation method using the embodiment shown in FIG. 1. 1...Substrate, 2...Protective film, 3...
...Information film, 4...Auxiliary film, PA, Ph...Laser power, Ho...
・External magnetism? A place for protection. Agent: Susumu Uchihara, Patent Attorney, Figure 2, Figure 1

Claims (1)

[Claims] 1. A magneto-optical disk comprising a substrate, an information film formed on the substrate, and an auxiliary film whose saturation magnetization and coercivity are larger than that of the information film and whose Curie temperature is also higher than that of the information film.