JPH0266751A - magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To additionally improve reproduction performance by providing a transparent film for light interference between a light transparent substrate and a magnetic film and forming the transparent film of a material which causes a change in refractive index by the light and heat of laser. CONSTITUTION:A chalcogenide film is formed as the transparent film 2 for light interference on the polycarbonate substrate 1 and the magnetic film 3 and a protective film 4 are provided thereon to form the recording medium. The change in the refractive index arises in the chalcogenide film 2 and the reflectivity changes accordingly when this medium is irradiated with the laser light. The quantity of the light necessary for a signal level reflects at the time of recording and the balance is inverted in magnetization for the purpose of recording. The larger quantity of light is obtd. at the time of reproducing and further, the refractive index restores the original value when the magnetization is returned by erasing. The reproduction performance is additionally improved by forming the transparent film of the material which is changed in the refractive index in such a manner.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rewritable magneto-optical recording medium, and particularly to a magneto-optical recording medium that improves reproduction performance by increasing the amount of reflected light during reproduction. be.

[Conventional technology]

In recent years, magneto-optical recording media that utilize magneto-optic effects have been actively researched and developed as rewritable optical recording media.
In some cases, it has even been put into practical use. This magneto-optical recording medium has the advantages of large-capacity, high-density recording, non-contact recording and playback, and ease of access, as well as the ability to overwrite document information files, video and still image files, and computer memory. It is expected that it will be used for

The above-mentioned magneto-optical recording medium has a perpendicular magnetization film, that is, a magnetic film having an easy magnetic axis in a direction perpendicular to the film surface, as a recording layer, and information can be recorded, reproduced, and erased by irradiating a laser beam and applying a magnetic field. It is now possible to do so.

In other words, to record information, the magnetization direction of the perpendicularly magnetized film is aligned in a certain direction in advance, a laser beam is focused on a minute part of the perpendicularly magnetized film, and only that part is heated to lose its magnetization. When the temperature returns to room temperature, a magnetic field is applied to the part so that the direction of magnetization is opposite to that of the surrounding area, thereby magnetizing the part to form a bit.

Generally, information is reproduced by irradiating the recording layer with a laser beam for reproduction (power is lower than that for recording), and using the magnetic Kerr effect, in which the direction of rotation of the polarization plane of the reflected beam differs depending on the magnetization direction of the irradiated part. Use and do it.

Information is erased by irradiating the recorded bits with a laser beam and applying a magnetic field in the opposite direction to the magnetic field used during recording.

On the other hand, one of the characteristics required of magneto-optical recording media is good reproduction performance. This reproduction performance is evaluated by a figure of merit, /Fak (R: reflectance, θ,; Kerr rotation angle), and it is said that the larger the figure of merit, that is, the larger the reflectance R and the Kerr rotation angle θ, the better.

Conventionally, in order to improve reproduction performance, many efforts have been made to obtain recording materials with as large a Kerr rotation angle θ□ as possible, and various recording materials have been published in patent publications, literature, and the like. Furthermore, in order to increase the Kerr effect, a technique has been proposed in which a transparent film for optical interference is provided between the substrate and the magnetic film (Japanese Patent Application Laid-Open No. 18546/1983, etc.). In this way, conventionally, in order to improve playback performance, the Kerr rotation angle θ
The reality is that attention has been focused only on .

[Problem to be solved by the invention]

However, it has been found that there is a limit to the reproduction performance by improving only the Kerr rotation angle θ as in the past. On the other hand,
In order to respond to recent advances in speed and precision of information processing,
Further improvements in playback performance are expected.

Therefore, in view of this point, it is an object of the present invention to provide a magneto-optical recording medium with further improved reproduction performance.

[Means and actions for solving the problem] As mentioned above,
It is said that the reproduction performance is better as the reflectance R and the Kerr rotation angle θ are larger. Here, there is a limit to the improvement of force per rotation angle θ. Therefore, when focusing on the emissivity R, when recording with a laser beam, it is desirable that the amount of light necessary for the signal level is reflected, and the remainder is used effectively by inverting the magnetization for recording.

Furthermore, during reproduction, it is desirable that as much laser light as possible is reflected and used as a signal.

In other words, if there is a minimum amount of reflection when recording and a larger amount of reflection when reproducing, the reproducing performance can be further improved.

The present inventor has completed the present invention as a result of extensive research while taking the above points into consideration.

That is, in order to achieve the above object, according to the present invention,
A magneto-optical recording medium in which a transparent film for optical interference is provided on a transparent substrate directly or via an underlayer, a magnetic film is provided on the transparent film, and a protective film is further provided on the transparent film,
There is provided a magneto-optical recording medium, characterized in that the transparent film is made of a substance that causes a change in refractive index due to the light heat of a laser.

As a substance that causes a change in refractive index due to the light heat of the laser, for example, at least 1% of chalcogen (S, Se, Te) is used.
Those containing at least one kind of compositional element are preferably used.

As a specific example of the compound, As3SeSnS4G
e, As, □5e4STe,, Ge□,, GcJS
Examples include chalcogenides (compounds containing chalcogen) such as bSnSe, AsSe, and 5bGea.

It has been found that when the above-mentioned substance is used in a transparent film provided between a substrate and a magnetic film, the refractive index changes before and after magnetization reversal, and the reflectance changes accordingly. That is, the amount of reflection is minimal during recording, and changes to a larger amount during reproduction. This makes it possible to further improve the reproduction characteristics. It was also found that if the magnetization of these materials is restored to its original state through an erasing action, the changed refractive index will also return to its original state. This reversibility allows application to rewritable magneto-optical recording media.

〔Example〕

The present invention will be explained in detail below with reference to Examples.

On a polycarbonate (PC) substrate, a chalcogenide film As3SeSnS4Ge was deposited to a thickness of 800 mm as a transparent film for optical interference by RF (radio frequency) sputtering, and then a magnetic film (FeCo) was deposited on top of it to a thickness of 700 mm. Then, a protective film of SiN was deposited to a thickness of 900 nm to obtain a magneto-optical recording medium having a film structure as shown in FIG. In the figure, 1 is a substrate, 2 is a transparent film for optical interference, 3 is a magnetic film, and 4 is a protection film. Moreover, the conditions for the above-mentioned span length are as follows.

・One chamber, multiple targets (batch type) ・Distance between target and substrate 1980 mm ・Vacuum degree (background) 1 to 5 X LP' Torr (during sputtering) 4-9 X 1O-3 Torr (Ar gas) ・Apply Power 0.75kW (RF 13
．． 6117)・Sputter rate 3-5 people/s
ec When recording is performed on the magneto-optical recording medium prepared as described above using a semiconductor laser with a wavelength of 820 nm, 23.1% of the total amount of light is reflected, and the remaining 76.9% is absorbed by the magnetic film, causing magnetization. The temperature rise necessary for reversal occurs, and the magnetization is reversed. At this time, it was found that a change in refractive index occurred in the chalcogenide film As3SeSnS4Ge as shown in Table 1. That is, the refractive index changed from 2.3 to 2.1 before and after the reversal of magnetization. Along with this, the reflectance changed from 23.1% to 26.7.

Table 1 It was also found that if the magnetization is returned to its original state by the erasing action, the refractive index of the chalcogenide film also changes from 2.1 to 2.3 and returns to its original state. This is thought to be due to the photothermal effect of the laser, which causes a compositional change in the chalcogenide film, in addition to the effect of magnetization reversal. Here, FIG. 2 shows a conceptual diagram of the above phenomenon.

When the playback performance of the magneto-optical recording medium of this example was evaluated, the figure of merit (1θ, ) was ≠] x 003 = 0.144
By improving from ≠, 267×0.3=0.155, the C/N became 53 dB, which was 4 dB better than the conventional one in which no refractive index change occurred (49 dB).

In addition, as a transparent film for optical interference, chalcogenide film As,
□Se,,,Te1. Ge□. , Ge3SbSnSe5
, As5e4SbGe3 were used to prepare a magneto-optical recording medium in the same manner as in the above example, and the reproduction performance thereof was evaluated. As a result, effects equivalent to those described above could be obtained.

〔Effect of the invention〕

As explained in detail below, according to the present invention, the protective film for optical interference provided between the substrate and the magnetic film is made of an oval material that causes a change in refractive index due to the light heat of the laser. With this change in refractive index, the reflectance changes so that a minimum amount of reflection is obtained during recording and a larger amount of reflection is obtained during reproduction, making it possible to further improve reproduction performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the film structure of a magneto-optical recording medium according to the present invention, and FIG. 2 is a conceptual diagram of a change in refractive index occurring in a transparent film for optical interference of a light distribution magnetic recording medium. 1... Substrate 2... Transparent film for optical interference 3, Magnetic film 4... Protective film Patent applicant Rico Co., Ltd.

Claims (1)

[Claims] (1) A transparent film for optical interference is provided on a transparent substrate directly or via an underlayer, and a magnetic film is provided on the transparent film,
A magneto-optical recording medium further comprising a protective film provided thereon, wherein the transparent film is made of a substance that causes a change in refractive index due to the light heat of a laser.