JPS61131257A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To improve recording and reproducing characteristics and the shelf stability by providing a reflective layer obtained by mixing a substance having low absorption to light of specified wave length and a substance having high reflectance to the light in the specified ratio. CONSTITUTION:A reflective layer 13 is formed with a mixture of a substance having low absorption to the wavelength of reproduced light and a substance having high reflectance to the wavelength. The content of the substance having low absorption is preferably regulated to the range 0.80-0.95. The reflective layer fills simultaneously the reflecting function and the phase modulating function. Accordingly, reproduced light transmitted through a magnetic recording layer 12 and undergoing Faraday rotation is reflected by the reflective layer 13, transmitted through the magnetic recording layer 12 while undergoing Faraday rotation, and detected as a signal having high S/N due to an increase in the polarization angle. Since linearly polarized incident reproduced light is reflected by the reflective layer 13 as circularly polarized light, still higher S/N can be obtained by aligning the light optimally with an analyzer by utilizing a phase plate. Moreover, the reflective layer 13 is hardly oxidized, and the recording and reproducing characteristics and the sheef stability can be improved.

Description

Detailed Description of the Invention (Technical Field) The present invention is used in magneto-optical memories, magnetic recording, display elements, etc., and can read recorded information using magneto-optic effects such as the magnetic Kerr effect or the Faraday effect. It relates to magneto-optical recording media.

(Prior art) Research into optical memory, which optically reads information recorded on various recording media, has been actively conducted, and in recent years, with the development of laser light sources and optical elements, high-density and large-capacity It is attracting attention as a memory of. As a type of such recording media, a magneto-optical recording medium is known in which magnetically stored information is read out using the magneto-optic effect. A magneto-optical recording medium has a magnetic film having an axis of easy magnetization perpendicular to the film surface as a recording layer. Further, for example, by magnetizing this recording layer in one direction and heating a portion by spot irradiation with a laser beam, information is recorded as a reversal of magnetization. Information is optically read out from the medium on which information is recorded in this manner using magneto-optical effects such as the magnetic Kerr effect and the Faraday effect. It is also possible to erase the recorded information by heating a part or the entire surface of the medium within an externally applied magnetic field.

In addition, the material for the magnetic film ranges from polycrystalline thin films such as MnB1 to G.
Transition metals (Fe,
Co, Ni, etc.) and rare earth metals (TI), Dy,
Amorphous alloy thin films with Gd, Ho, etc.) are being considered.

On the other hand, the magneto-optical recording medium as described above has a drawback in that the reproduced signal level is low. In particular, in the reproduction method using the Kerr effect, since the Kerr rotation angle is small, the signal-to-noise ratio (8
/N) was difficult to increase. Therefore, conventional methods have been to improve the magnetic material constituting the recording layer, or to add silicon monoxide (Sin) or silicon dioxide (
Efforts have been made to increase the Kerr rotation angle by forming a dielectric thin film of Sin, ) and utilizing multiple reflections onto the recording layer. Also, JP-A-58-6541 and JP-A-58-
As disclosed in Japanese Patent No. 6542, a method has also been proposed in which a magnetic recording layer is made sufficiently thin and a metal reflective layer is provided on the back surface to obtain a large reproduced signal by utilizing the Kerr effect and Faraday effect. An example of such a recording medium is shown in FIG. In FIG. 2, 21 is a transparent substrate, 22
23 is a magnetic recording layer, 23 is a metal reflective layer, and 24 is a protective layer. In addition, as shown in Figure 3, by providing a transparent dielectric layer between the magnetic recording layer and the metal reflective layer, and by optimally selecting the materials and film thicknesses of these three layers, it is possible to reproduce a reproduced signal with an even higher S/N. There are also reports that it is possible to obtain (J.

Appl, Phys, VOI-53, A6 p4
485-4494).

In FIG. 3, 31 is a transparent substrate, 32 is a magnetic recording layer, 33 is a transparent dielectric layer, 34 is a metal reflective layer, and 35 is a protective layer. Here, the transparent dielectric layer 33 separates the light reflected at the interface between the amorphous magnetic thin film layer 32 and the light-transmitting substrate 31 and the light reflected by the metal reflective layer 34 . It gives a phase difference to the light reaching the interface of 31, reduces the reflectance of the medium, and serves to apparently increase the rotation angle of the plane of polarization due to the magneto-optic effect.

However, all of the above conventional magneto-optical recording media
Since the reflective layer was formed of a metal thin film (100 to 600 layers), it had the disadvantage of being easily oxidized. When the reflective film is oxidized, it causes a decrease in recording sensitivity, an increase in errors during reproduction, and signal deterioration, and furthermore, there are disadvantages in that the recording layer is also easily oxidized. In addition, transparent dielectrics and
In order to improve the 8/N ratio in the body layer, it is necessary to control the film thickness accurately and uniformly, which has been difficult to produce due to problems such as reproducibility.

(Summary of the Invention) An object of the present invention is to provide a magneto-optical recording medium from which a reproduced signal with a high S/N ratio can be obtained and which has excellent storage stability.

Another object of the present invention is to obtain a reproduced signal with a high S/N ratio,
Another object of the present invention is to provide a magneto-optical recording medium that is easy to produce.

The above-mentioned object of the present invention is to provide a recording layer made of a magnetic film having an axis of easy magnetization perpendicular to the film surface; This is achieved by constructing the magneto-optical recording medium from a reflective layer made of a mixture of a material with low absorption and a material with high reflection.

(Example) The structure of an example of the magneto-optical recording medium of the present invention is shown in FIG. In FIG. 1, 11 is a transparent substrate, 12 is a magnetic recording layer, 13 is a reflective layer, and 14 is a protective layer. The transparent substrate 11 is made of glass or plastic, for example. The magnetic recording layer 12 is formed from a magnetic film having an axis of easy magnetization perpendicular to the film surface. Such a magnetic film is made of GdTbFe, which has a large Kerr rotation angle.

Tb Dy Fe, Gd Dy Fe,, Gd
Preferably, rare earth-transition metal amorphous alloys such as FeCo are used.

The information magnetically stored in the magnetic recording layer 12 is read out using the magneto-optic effect by irradiating reproduction light through the transparent substrate 11.

That is, the reproduction light becomes modulated light whose plane of polarization is rotated according to the information, and information is reproduced by converting the rotation of the plane of polarization into a change in light amount using an analyzer or the like and detecting it.

Reflection J? J13 is formed of a mixture of a material with low absorption and a material with high reflection with respect to the wavelength of the reproduction light. With this configuration, the reflective layer 13 simultaneously performs a reflective function and a phase modulation function. Therefore, the magnetic recording layer 1
2 and undergoes Faraday rotation, the reproduced light passes through the reflective layer 1.
3, the light passes through the magnetic recording layer while undergoing Faraday rotation again, and is detected as a high signal of 87N due to an increase in the rotation angle of the plane of polarization. Furthermore, unlike a metal film that reflects linearly polarized light, the reflective layer 13 is made of a mixture as described above, so it reflects the input reproduced light as linearly polarized light as elliptical polarized light, so a phase plate is used. By doing so and optimally aligning it with the analyzer, it is possible to obtain a high S/N ratio again.

Suitable materials for forming the reflective layer 13 that have low absorption include metal or semimetal oxides, fluorides, sulfides, iodides, and organic polymers at the wavelength of normal reproduction light such as a laser. There is.

Moreover, as a single substance, any material may be used as long as it transmits most of the reproduction light, but it is preferable that the imaginary part of the refractive index is 0.01 or less in the wavelength range of the reproduction light. As the material of the reflective layer 13 that has a large reflection of the reproduced light, it is desirable to use a substance that alone has a reflectance of 80% or more in the wavelength range of the reproduced light. Specifically, Cu+ A g +
Metals such as AuTAe are suitable. The reflective layer 13 made of such a material may be made of, for example, % as described above.
% Because the drawing is such that the metal is dispersed in the electric body,
Compared to conventional metal reflective layers, it is resistant to oxidation and has excellent storage stability.

The composition ratio of the substance with low absorption (Mu) and the substance with high reflection (Mr) in the reflective layer 13 varies depending on the wavelength of the reproduction light or the substance used, but usually the substance with high reflection has a composition ratio of the substance with high reflection to the whole. is preferably in the range of 0.80 to 0.95 (0.80<x<0.95 when the reflective layer consists of Mlx to fui-x). 0.80
If it is less than 0.95, a sufficient reflectance cannot be obtained; if it exceeds 0.95, a problem arises in storage stability. The thickness of the reflective layer 13 is
It varies depending on the constituent materials or the above composition, but usually 700
~3000λ is suitable. Moreover, such a reflective layer 1
It is desirable that the film thickness of the magnetic recording layer 12 when the magnetic recording layer 3 is provided is 100 to 1000 λ so that a sufficient amount of light can be transmitted.

Various methods can be considered for forming the reflective layer 13;
As mentioned above, in the case of forming a mixture of a dielectric and a metal, it is suitable to simultaneously deposit them by sputtering, electron beam evaporation, resistance heating evaporation, or the like. Here, the phase difference of the reproduction light reflected by the reflective layer 13 is:
is mostly determined by the composition of the mixture constituting the reflective layer 13.

Since such a composition can be controlled with very high precision, it is easier to create a magneto-optical recording medium that provides the desired phase difference than when controlling the thickness of the transparent dielectric layer as in the past. .

In FIG. 1, the protective layer 14 protects the reflective layer 13 from scratches, dust, moisture, oxygen, etc., but it is not always necessary depending on the material of the reflective layer.

The accent protection layer 14 may be formed by coating an organic polymer film, or may be formed using an oxide (SiO, 5in2, etc.), nitride (Si
, N, etc.), an inorganic material such as sulfide, or a metallic material may be provided by vapor deposition.

In the magneto-optical recording medium of the present invention, an auxiliary layer is provided as necessary. For example, it is also possible to provide a heat insulating layer 1ψ between the transparent substrate 11 and the magnetic recording layer 120 in FIG. 1 as an auxiliary layer, such as an antireflection layer or an organic polymer with low thermal conductivity.

In addition, a medium capable of double-sided recording can also be realized by a method such as bonding with the index mark or trough on the inside.

Hereinafter, the present invention will be specifically explained with reference to comparative examples and examples.

A magneto-optical recording medium was manufactured through the following steps. Diameter 1
A smooth glass substrate of 20 mm and 1.5 mm thickness was cleaned, and a curable silicone resin (SR-2410, manufactured by Toray Silicone Co., Ltd.) was coated on one side with a spinner coater to a dry film thickness of 0.5 μm. I painted it to look like this. The drying conditions were 150°C for 12 hours. The silicone resin is used to prevent the dissipation of heat generated when the magnetic recording layer is irradiated with a beam.

Next, silicon monoxide (Sin, purity 99.9%) was formed as an antireflection layer on the surface of the silicone resin layer by electron beam evaporation to a predetermined thickness that minimized the reflectance. This thickness is different from the currently used semiconductor laser (GaA
The thickness is approximately 0.1 μm, which is the wavelength of 820 nm rn of s A,e ) divided by four times the refractive index of silicon monoxide. Next, as a magnetic recording layer, Fe0.76 GdO,
An amorphous thin film having a composition of 12Tb0.12 was formed to a thickness of 0.02 μm using a sputtering device. Further, as a protective layer, silicon monoxide (SiO purity 99.9%) was formed to a thickness of 0.3 μm by electron beam evaporation. Pit recording and reproduction were performed on this magneto-optical recording medium using an optical head from the glass surface side. The recording optical head used a semiconductor laser (820 nm) with an output of 20 mW as a light source, and was configured to irradiate the surface of the recording layer as a minute spot of ~1.2 μmφ. Further, an electromagnet was arranged so as to be able to apply a magnetic field perpendicular to the surface of the recording layer. A disk-shaped magneto-optical recording medium was rotated to uniformly magnetize the recording layer, and then a laser was pulsed to record a 5 MHz signal in pits.

For reading and reproducing, a 10 mW semiconductor laser was used as a light source, and the recording layer was irradiated in the same manner as during recording, and reflected light was detected via a polarizer. The C/N value (S/N value in the center frequency band of the signal) of the reproduced signal was 24 dB.

Feo, 76Gdo, t2Tbo,
up to the recording layer consisting of
A metal reflective layer as shown in the table was provided. Further, a protective layer of silicon monoxide having a thickness of 0.3 μm was provided on the metal reflective layer. Recording and reproduction were performed in the same manner as Sample 1, and the C/N values of the reproduced signals as shown in Table 1 were obtained. ) Samples 6 to 21 (invention) Feo7e Gdo12Tbo,
A recording layer consisting of tz was formed, and a reflective layer was further formed by co-evaporating a substance with low absorption (Mu) and a substance with high reflection (Ml) by sputtering as shown in Table 1. The composition ratio is indicated by X when the reflective layer is composed of Mlx Ml-x.

A protective layer of silicon monoxide with a thickness of 0.3 μm was provided on this reflective layer.

Next, the recording and reproducing characteristics (reproducing C/N value) of these samples were measured. The experimental conditions were the same as Sample 1, and the laser output for recording was 7 mW on the medium surface.

The recording signal was a 5 MHz pulse signal with a duty of 50%, the laser output for reproduction was 2 mW on the medium surface, and the C/N value was evaluated with a band width of 30 KHz.

The C/N value is considered to indicate the effects of both the size of the recording pit (ie, recording sensitivity) and the magnitude of the magneto-optic effect of the medium. These measured C/H values are summarized in Table 1.

Storage test samples 1 to 21 were subjected to a storage test for 2 months in an environment with a temperature of 45°C and a relative humidity of 95%, and the media after the test were recorded and reproduced under the same conditions as above, and the C/ The N value was measured. The results are shown in the last column of Table 1.

As can be seen from Table 1, the magneto-optical recording medium of the present invention is
It exhibits better recording/reproducing characteristics and storage stability than conventional media without a reflective layer or with a metal reflective layer.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the structure of an embodiment of the magneto-optical recording medium of the present invention, FIG. 2 is a schematic sectional view showing an example of the structure of a conventional magneto-optical recording medium, and FIG. 3 is a schematic sectional view showing the structure of a conventional magneto-optical recording medium. FIG. 3 is a schematic cross-sectional view showing another example of the configuration of a recording medium. 11... Transparent substrate, 12... Magnetic recording layer, 13... Reflective layer, 14...
...protective layer.

Claims (1)

[Claims] (1) In a magneto-optical recording medium having a recording layer made of a magnetic film having an axis of easy magnetization perpendicular to the film surface and a reflective layer provided on the recording layer, the reflective layer is exposed to light of a predetermined wavelength. In contrast, it consists of a mixture of a substance with low absorption and a substance with high reflection, and the composition ratio of the substance with high reflection to the entire mixture is 0.80 to 0.9.
5. A magneto-optical recording medium characterized by being present in the range of 5.