JPH0619860B2 - Magneto-optical record carrier - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an improvement of a record carrier of a magneto-optical memory used for recording information.

2. Description of the Related Art In recent years, it has been strongly desired to put a rewritable large-capacity optical disc into practical use as the information-oriented society advances. It has recently been confirmed that the magneto-optical memory, which has been attracting particular attention among them, has excellent characteristics as a digital memory.

By the way, the magneto-optical record carrier is a rare-earth transition metal amorphous magnetic substance because of the Curie temperature, which is the main factor that determines the recording sensitivity, the Kerr rotation angle that determines the quality of the reproduction signal, and the constraints such as film formation at low temperature. Is used. This rare earth transition metal is composed of an alloy of at least one of Fe, Co and Ni and at least one of rare earth elements centered on Gd, Tb and Dy. Specifically, they are TbFe, GdTbFe, TbFeCo, and the like.

However, these rare earth-transition metal magnetic materials including TbFe generally have the drawback of poor corrosion resistance. That is, since rare earths are extremely susceptible to oxidation, their magnetic properties change when exposed to the atmosphere or water vapor, and the easy axis of magnetization perpendicular to the film surface is impaired, and eventually the transition metal is also oxidized and becomes transparent. Become.

In order to eliminate such a defect, conventionally, in the structure of a magneto-optical record carrier, a protective film such as SiOx, SiNx, Al ₂ O ₃ , AlN which is a transparent dielectric is provided on the magnetic layer. Set up,
Alternatively, a disk structure in which an inert gas is contained has been proposed (for example, JP-A-59-140652).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, a dielectric film made of an oxide or a nitride has a drawback that a thin film does not have a sufficient effect on corrosion resistance and a thick film causes cracks. , Not enough effect has been obtained.

Further, even in the structure in which the inert gas is confined, the oxidizing effect of the rare earth is extremely strong, so that the sufficient effect cannot be obtained due to the small amount of oxygen or water vapor contained in the inert gas.

In view of the above-mentioned problems, the present invention provides a magneto-optical record carrier having a corrosion resistance superior to that of a conventional one by using an appropriate protective layer.

Means for Solving the Problems To achieve this object, the magneto-optical record carrier of the present invention has a structure in which a magnetic film is formed on a substrate and a dielectric film and a zirconium film are further laminated. The dielectric film and the zirconium film are formed on the rare earth transition metal magnetic layer by a known method such as vacuum deposition or sputtering.

It is desirable to carry out the series of thin film production in the same vacuum chamber in order to avoid adsorption of oxygen and water vapor at the interface.

The working dielectric film plays a role of avoiding a decrease in recording sensitivity that occurs when the zirconium film is directly formed on the magnetic film, and is composed of an oxide film and a nitride film having a small thermal conductivity. The thickness of this dielectric film is preferably 1000Å to 5000Å. If the thickness is less than this lower limit, the heat insulation effect becomes insufficient, and a decrease in recording sensitivity cannot be avoided. If it is thicker than the upper limit, cracks are likely to occur, and on the contrary, corrosion resistance is deteriorated. On the other hand, the thickness of the zirconium film is preferably 2000Å to 10000Å. If it is less than this lower limit, the corrosion resistance effect is weakened and the protective layer cannot have a satisfactory function. On the other hand, if the thickness is more than the upper limit, peeling of the protective layer may occur due to an increase in internal stress.

With this configuration, as compared with the conventional magneto-optical record carrier, the corrosion resistance can be improved more than before without causing a decrease in recording sensitivity.

Examples Example 1 An example of the present invention will be described in detail below.

For the thin film formation, a binary simultaneous vapor deposition apparatus equipped with two electron beam evaporation sources is used. After evacuation to 2 × 10 ⁻⁷ Torr, a glass substrate having a diameter of 120 mmφ is rotated at 60 rpm to form a TbFe film of about 1000 Å. The vapor deposition rates are Tb4Å / sec and Fe6Å / sec, respectively. Immediately thereafter, 2000 liters of SiO is formed at a vapor deposition rate of 10 liters / sec, and a zirconium film is further formed at 3000 liters at a vapor deposition rate of 10 liters / sec. This disk is further bonded to another glass substrate with an ultraviolet curable resin. Using the magneto-optical record carrier manufactured in this way, a recording magnetic field 300
As a result of recording at oe and disk rotation speed of 600 rpm, it was possible to record at a recording power of 3 mW or less at a position with a diameter of 80 mm.

For comparison, those without a protective layer, SiO2000Å
The following table shows the laser power required for recording under the same conditions for those having only the protective layer, and those having the zirconium film 3000Å on the magnetic body directly formed without the dielectric film.

Furthermore, these four types of record carriers were put in a constant temperature and constant humidity chamber at a temperature of 60 ° C. and a relative humidity of 90% to perform a corrosion resistance test. The results are shown in FIG. As a parameter for evaluating the corrosion resistance, the amount of change in coercive force caused by selective oxidation of rare earth is shown with an initial value of 1. The larger the change in coercive force, the more severe the corrosion is. It can be seen that the zirconium film improves the corrosion resistance.

Example 2 A disk was produced in the same manner as in Example 1 except that only the SiO film thickness was changed, and the laser power required for recording was determined in the same manner as in Example 1 and the results are shown in FIG. Shown in. When the film thickness is 1000 Å or more, a remarkable heat insulating effect is exhibited, and recording can be performed with low laser power.

Example 3 A disk in which only the zirconium thin film was changed was prepared in the same manner as in Example 1, placed in a constant temperature and humidity chamber at a temperature of 60 ° C. and a relative humidity of 90%, and the change in coercive force after 1000 hours was measured. . The results are shown in FIG. It can be seen that a remarkable corrosion resistance effect is exhibited at a film thickness of 2000 Å or more.

Example 4 A disk similar to that of Example 1 was prepared except that the recording magnetic film TbFe was changed to GdTbFe, and the same corrosion resistance test as in Example 1 was performed. As a result, the same as shown in FIG. The result was obtained.

In this example, SiO was used as the dielectric film,
The present invention is also effective when a nitrogen compound such as Si ₃ N ₄ , AlN, BN, or GaN is used as the dielectric film.

In this embodiment, the laminated disc is used, but the present invention is also effective for a single plate structure disc.

EFFECTS OF THE INVENTION According to the present invention, by providing a zirconium film on the magneto-optical recording film, the corrosion resistance can be remarkably improved as compared with the conventional one, and a dielectric film having a small thermal conductivity is formed at the interface with the zirconium film as a recording film. By forming the above, it is possible to realize an excellent magneto-optical record carrier that can obtain the effect of avoiding the problem of the decrease in recording sensitivity.

[Brief description of drawings]

FIG. 1 is a characteristic diagram of a magneto-optical record carrier according to the present invention which does not have a protective layer, only a protective layer of SiO film and only a protective layer of zirconium film, and FIG. 2 is a magneto-optical record carrier according to the present invention. FIG. 3 is a film thickness-dependent characteristic diagram of the dielectric film showing the recording sensitivity, and FIG. 3 is a film thickness variation characteristic diagram of the zirconium film of the magneto-optical record carrier according to the present invention.

Claims (1)

[Claims] 1. A rare earth transition metal magnetic thin film laminated directly or via a transparent dielectric layer on an optically transparent substrate, and a zirconium thin film protective layer further laminated via a dielectric layer. A characteristic magneto-optical record carrier.