JPH0259529B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a magneto-optical recording medium.

Recently, magneto-optical recording media have been attracting attention as a new method that enables high-density recording and reproduction using laser light. It takes advantage of the fact that the plane of polarization rotates when doing so.
Therefore, it is desired that this rotation angle, that is, the force-rotation angle be large. As a method of increasing this force-rotation angle, SiO, SiO ₂ , ZnS, Si ₃ N ₄ ,
It is known to provide a transparent dielectric layer such as AIN, TiO ₂ , Al ₂ O ₃ , Ta ₂ O ₃ , etc. In this case, among these materials that increase force-rotation, the one with a higher refractive index It is also known that there is an effect of increasing the force-rotation angle (enhancement effect). In particular, when reproducing by irradiating laser light from the transparent substrate side, the refractive index of the glass or PMMA used as the substrate is approximately 1.5, so the refractive index is even higher than when reproducing from the air side. Substance is preferred.

The inventor believes that the material used to increase the force-rotation angle only needs to be transparent to the laser wavelength of around 800 nm, and does not need to be transparent over the entire visible light range like conventional dielectric materials. As a result of examining various materials from the viewpoint of 3.0 to 3.8, we decided to use amorphous Si, which has a very high refractive index of 3.0 to 3.8 and has a certain degree of transmittance to the wavelength of laser light, in place of the conventional transparent dielectric layer. It has been found that the use of this material provides a force-rotation angle enhancement effect that is significantly greater than that of conventional dielectric materials. In this case, amorphous
Since the optical absorption edge of Si is around 1000 nm, laser light tends to be absorbed to some extent at 800 nm. Therefore, if the energy gap is increased and the optical absorption edge is moved to the shorter wavelength side, the optical absorption edge at around 800 nm can be absorbed. We considered the possibility of reducing optical absorption and further increasing the force-rotation angle, and as a way to increase the energy gap of amorphous Si, we added H, F, C, N, and O to the amorphous Si to increase the force. −
It was found that this results in an increase in the rotation angle. As a result of many experimental studies, one or two of these elements
It has been found that the above effects can be obtained by mixing 50 at% or less, preferably 30 at% or less, of amorphous Si with at least 50 at% of amorphous Si.

Thus, the present invention provides a magneto-optical recording medium that satisfies the above requirements, and is comprised of an amorphous Si layer provided on one or both sides of a magnetic layer as a layer for increasing the force-rotation angle. Furthermore, the present invention provides a magneto-optical recording medium that has the effect of increasing the force-rotation angle.
It consists of a Si layer.

The invention will be further explained with reference to examples.

The amorphous Si layer can be formed using the well-known sputtering method, RF
It is formed on the upper surface of a transparent substrate such as glass by a sputter method plasma CVD method, vapor deposition method, ion plating method, optical CVD method, etc. a, in which one or more elements of H, F, C, N, and O are mixed into amorphous Si (hereinafter abbreviated as a-Si);
-Si:H, a-Si:F, a-SiC:H, a-SiN
-H, a-SiO: To form a layer such as H, for example, H ₂ gas, N ₂ gas, O ₂ gas, SiH ₄ gas, SiF ₄
Introducing single or mixed gases such as
The RF sputtering method or plasma CVD method was used. For mixing C, a target consisting of a large number of graphite pellets placed on a Si target was used.
25at%Tb-Fe was applied to the surface of the a-Si layer created in this way, the a-Si layer mixed with elements such as a-Si:H, etc.
A film (1000 Å) was created, and a 1000 Å SiO ₂ film was further formed on it as a protective film. Incidentally, in order to examine the relationship between the thickness and the force-rotation angle of the layers containing the above elements such as the a-Si layer and the a-Si:H layer, the above-mentioned samples having different thicknesses were prepared. An 830 nm semiconductor laser was used to measure the force-rotation angle. Furthermore, the light absorption rate and refractive index were measured using each sample on which the above-mentioned Tb-Fe film and SiO ₂ film were not formed.

FIG. 1 shows the change in thickness of the a-Si layer and the change in force-rotation angle. For comparison, we also show the measurement results when _two TiO layers were formed as an example of a conventional dielectric. As is clear from Fig. 1, the force-rotation angle is approximately 15 min with only the Tb-Fe film, but it is observed that when the a-Si layer of the present invention is formed, the force-rotation angle increases to a maximum of 40 min. It is recognized that the a-Si layer has a superior effect of increasing the rotation angle compared to the dielectric material, with the conventional TiO ₂ dielectric material having a maximum rotation angle of 25 min and over the entire change in film thickness. The maximum film thickness is 650 Å for the TiO ₂ layer, while it is 450 Å for the a-Si layer. This is because TiO ₂ has a refractive index of 2.3, whereas a-Si has a large refractive index of 3.7.

This maximum force-rotation angle was obtained at 450 Å a-
When the light absorption rate of the Si layer alone was measured, it was 10% for 830 nm laser light. In order to reduce this light absorption rate, it was found that when an a-Si layer added with H, C, O, N, etc. was created, the light absorption rate decreased. The relationship between the amount of the element to be added and the force-rotation angle was examined. FIG. 2 shows the relationship between the amount of element added and the force-rotation angle in the a-Si layer with a thickness of 450 Å, which provides the maximum force-rotation angle.

As is clear from this figure, the force-rotation angle increases with increasing addition amount for all additive elements, reaches a maximum value at about 10 to 30 at%, and then decreases.
It was confirmed that the force-rotation angle could be maintained at 40 min or more up to about 50 at%.

From the above, in the region where the amount of addition is small, reducing the amount of light absorption contributes to enhancing the force-rotation angle, and if the amount of addition is increased beyond that, the amount of light absorption almost disappears, but the refractive index This means that the force-rotation angle gradually decreases as the decrease decreases. It was also found that a similar tendency for the force-rotation angle to increase was observed when two or more elements were mixed.

The results are shown in FIG. In the drawing, the amounts of each two types of elements are equal.

By adding one or more of these elements, the elements have a strong bonding force with Si atoms, resulting in an increase in the energy gap.

The above experiments were conducted for the case of reproduction from the transparent substrate side, but we also used a type that reproduced from the air side and a layer that increases the force-rotation angle between the translucent magnetic layer and the reflective layer (so-called Even in a type of magneto-optical recording medium that uses both Faraday rotation and force-rotation with an intervening enhancement layer, the a-Si layer of the present invention or H,
a containing one or more of C, N, F, and O
-It is extremely effective by using a Si layer.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between film thickness and force-rotation angle of a magneto-optical recording medium according to an embodiment of the present invention in comparison with that of a conventional magneto-optical recording medium, and FIG. 2 is a graph showing another embodiment of the present invention. A graph showing the relationship between the amount of one kind of additive element and the magnitude of force-rotation angle in the example, FIG.
FIG. 7 is a graph showing the relationship between the amounts of two types of additive elements and the magnitude of force-rotation angle in other examples of the present invention. FIG.

Claims (1)

[Claims] 1. A magneto-optical recording material comprising an amorphous Si layer provided on one or both sides of a magnetic layer as a layer for increasing the force-rotation angle. 2 H, F, C, N, on one or both sides of the magnetic layer.
50 at% of at least one element selected from O
1. A magneto-optical recording material characterized in that an amorphous Si layer mixed to a certain extent is provided as a layer for increasing force-rotation.