JPS61187140A - Photomagnetic disk - Google Patents

Abstract

PURPOSE:To obtain the title photomagnetic disk having excellent oxidation resistance, a long service life and excellent characteristics by specifying the composition ratio of the rare earth element Tb to the transition metal Co in a recording layer consisting of a rare earth element-transition metal amorphous alloy thin film. CONSTITUTION:An interference film 2, a TbCo film as a recording layer 3 and a protective layer 6 consisting of an interference film 4 and a light reflecting layer 5 are successively formed on a resinous substrate 1 having guide groove for tracking to constitute a photomagnetic disk. The composition ratio of Tb to Co in the recording layer 3 is regulated to 21-30(at%). Consequently, a photomagnetic disk having excellent oxidation resistance, a long service life and excellent characteristics can be obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a rewritable type magneto-optical device whose recording layer is a rare earth-transition metal amorphous alloy WIII having an axis of easy magnetization perpendicular to the substrate surface. Regarding discs.

[Technical background of the invention and its problems]

A rare earth-transition metal amorphous alloy thin film (abbreviated as RE-7M film) is produced by (a) forming a perpendicularly magnetized film on an inexpensive substrate by a film-forming method that is easy to apply industrially, such as sputtering or vacuum evaporation; Can be formed.

(b) Recording and erasing can be performed by irradiation with a low-power light beam from a semiconductor laser or the like, which is advantageous from a system perspective. (C) Since it is amorphous, it has the advantage of being able to form recording bits with the same shape as the spot shape of the recording laser beam without grain boundary noise, so it can be used as a recording layer material for rewritable magneto-optical disks. It is considered to be the most promising for practical application, and development efforts are being made in various places.

The characteristics of (a) to (C) above are rare earth elements (RE)
as Gd, Tb, Dy, Ho, and transition metal elements (
This is a characteristic generally possessed by an RE-7M film made of a combination of Fe and Co used as TM), but the more specific memory characteristics largely depend on the combination of RE and TM. different. Among these, the RE-7M film, whose main components are Dy and Ho as rare earth elements, has an insufficient Kerr rotation angle that contributes to the reproduced signal, and has no practical advantage as a recording layer for magneto-optical disks. Therefore, below,
Gd, Tb as rare earth elements, Fe as transition metal element
, Go will be narrowed down to the types of elements discussed.

The main RE-7M film materials developed so far as recording layers in rewritable magneto-optical disks include GdC.
o, GdTbCo (composition ratio of Tb in GdTb is 30at0% or less).

TbFe, TbFeCo (compositional component ratio of Co in FeCo is 15at0% or less).

There are GdTbFe and the like, but when these materials are used, there are the following problems. For example, TbFe.

When TbFeCo or GdTbFe is used as a recording layer, the Curie temperature is at most about 250°C, so it is quite advantageous in terms of recording and erasing characteristics, but since Fe is the main component, long-term storage is fundamentally important for memory. Establishing sexuality is inherently difficult.

In the case of optical disk memories, it is generally known that it is advantageous for the light beam to enter from the substrate surface side, as dust present near the focal point of the recording/reproducing light beam significantly increases the error rate. . Even in magneto-optical disks in which the recording layer is made of a material containing Fe as the main component of the transition metal element mentioned above, an oxidation-preventing film is provided on the surface of the recording layer opposite to the substrate surface to achieve a practically sufficient memory life. Although it is possible to form it as a protective layer, it complicates the disc manufacturing process. In other words, as mentioned above, one of the advantages of the RE-7M film is that it can be formed by easy industrial methods such as sputtering and vacuum evaporation. The formation of the anti-oxidation film that will be formed later will be of little value in dry processes unless sputtering or vacuum evaporation can be applied, and RE-TMII! +7) After formation, set the substrate temperature to RE-T.
The anti-oxidation film must be formed while keeping the temperature lower than the crystallization temperature of MII. However, it is inherently difficult to maintain the substrate at a low temperature and form a high-quality anti-oxidation film without pinholes by sputtering or vacuum evaporation, so it is necessary to form a molding material using a wet process, which prevents oxidation. Membrane formation processes cannot avoid complications. Furthermore, the formation of such an oxidation-preventing film has the disadvantage of increasing the cost of the disc, and it is also difficult to use acrylic or polycarbonate, in which it is easy to form a tracking guide groove for an optical head guide, which is impractical in practice. When transparent resin materials such as
Since the space between the -7M film and the recording/reproducing light beam is on the incident side, it is impossible to form anything other than an antioxidant film having an optical function. Therefore, RE-7 whose main component is the above-mentioned l''e
A magneto-optical disk having an M film as a recording layer has a problem in that it is extremely difficult to establish long-term storage stability.

These problems will become clear from the results of experiments conducted by the inventors, which will be explained in the Examples described below.

Furthermore, among the RE-7M films used in the recording layer of the conventional magneto-optical disk described above, GdCo, GdTb
Since Fe is not used as a transition metal element for Co, a practical life span can be achieved by taking anti-oxidation measures such as coating with an anti-oxidation film formed by low-temperature sputtering. However, on the other hand, when forming the recording layer, a perpendicularly magnetized film cannot be obtained using the vacuum evaporation method, and a perpendicularly magnetized film cannot be obtained unless the sputtering method places an excessive heat load on the substrate using bias sputtering. Therefore, when a practically advantageous resin substrate is used, heat load on the substrate becomes a problem. Furthermore, the coercive force inherent in these RE-7M films near room temperature is insufficient to stably hold recorded bits except in a very limited composition range near the compensation composition. However, there is a problem in that it is difficult to form a recording layer with uniform characteristics on a large-area substrate.

In this way, the RE-7M film, which has been developed as a recording layer for rewritable magneto-optical disks, has the following characteristics:
Long-term shelf life, ■ Resin substrate can be used. ■ A recording layer with uniform characteristics can be formed on a large-area substrate. It is difficult to satisfy these requirements at the same time, and there are major problems in putting any of them into practical use.

In order to solve the problems of the conventional RE-7M film mentioned above, the inventors added Co, which itself has excellent oxidation resistance, to the transition metal element.
TbCo is an RE-7M film that can be made into a perpendicular magnetization film with a sufficiently large coercive force near room temperature by combining this with Tb as a rare earth element and using a non-bias sputtering method or a vacuum evaporation method that places a small heat load on the substrate. We have already proposed a magneto-optical disk with a film as the recording layer (
8th Japanese Society of Applied Magnetics Academic Lecture Abstracts 148B-11
November 1984). In this report, there is no detailed study of the composition ratio, film thickness, optimal disk structure, etc. of the TbCo film. Further, for example, Japanese Patent Publication No. 54-41179 also exemplifies a TbCo film as one of the RE-7M films that can be used for the recording layer, but it does not disclose preferable composition conditions. However, these are important factors that cannot be ignored when trying to actually provide a magneto-optical disk that can be put to practical use.In particular, the composition ratio has a direct effect on the coercive force, recording sensitivity, etc. of the recording layer. This is thought to have a significant impact, and its optimization is extremely important.

[Purpose of the invention]

An object of the present invention is to provide a magneto-optical disk with excellent oxidation resistance, long life, and good characteristics.

[Summary of the invention]

In order to achieve this object, the present invention includes a substrate, a recording layer formed on the substrate and made of a rare earth-transition metal amorphous alloy thin film having an axis of easy magnetization in a direction perpendicular to the surface of the substrate; In this magneto-optical disk including a protective layer formed on the surface of the recording layer opposite to the substrate surface, the rare earth element in the recording layer is Tb, the transition metal element is Co; It is characterized in that the compositional component ratio of Tb in the composition is selected in the range of 21 [at, %] to 30 [at 0%].

〔Effect of the invention〕

According to the present invention, the TbC0 film as the RE-7M film constituting the recording layer uses Go, which itself has high oxidation resistance, as a transition metal element, so it has a much higher performance than a film using Fe or the like. It has a long lifespan. In addition, the TbCo film can be used with other RE-7M films using Co as the transition metal element, such as GdC.
Unlike O films, etc., it is a non-bias film with a small heat load on the substrate.
Since a perpendicular magnetization film can be easily obtained by a sputtering method or a vacuum evaporation method, it is possible to use a resin substrate which is practically preferable in various aspects without any problems. Moreover, since a perpendicularly magnetized film with sufficient coercive force can be obtained over a very wide range of compositional ratios of Tb, which is a transition metal element, it is possible to form a recording layer on a large-area substrate that is actually used. Uniform characteristics can be easily obtained even in cases where

Furthermore, in the present invention, such TbC.

In addition to the essential characteristics of the film, especially Tb in the TbCo film
By selecting the composition ratio within the above-mentioned range, it becomes possible to stably obtain recording bits equivalent to the spot size of the light beam by irradiating the low power light beam and applying a relatively low auxiliary magnetic field. That is, there are advantages in that recording stability and recording sensitivity are high, and excellent dynamic characteristics can be obtained.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a magneto-optical disk according to an embodiment of the present invention. In this figure, a substrate 1 is a resin substrate such as an acrylic plate having a tracking guide groove for guiding an optical head for recording and reproducing.

A first interference layer 2 is formed on this substrate 1, and a TbCo film as a recording layer 3 is formed on this interference layer 2.

Further, a second interference layer 4 and a light reflection layer 5 are sequentially formed on this recording layer 3. These second interference layer 4 and light reflection layer 5 constitute a protective layer 6 for the recording layer 3.

The first and second interference layers 2 and 4 are made of, for example, SigN+ sputtered films, and the light reflection layer 5 is made of an A.degree. C. vapor-deposited film.

Below, several experimental examples conducted to investigate the usefulness of the magneto-optical disk based on the present invention having this structure will be described.

In LLL2 Experimental Example 1, various RE-TMI! The following describes the results of an experiment conducted for the purpose of evaluating the oxidation resistance of the material itself. There have already been qualitative reports that RE-7M films containing Co as the main component as a transition metal element have better oxidation resistance than those containing Fe as the main component. etc. are Fe, Fe, etc. as transition metals.

-Co2°.

Fe,. A quantitative lifetime evaluation was performed on a TbFeCo perpendicularly magnetized film using -Co5°, Co (the subscript is the atomic ratio of Fe or Co in the transition metal), (Gd, .Tb, .)Co perpendicularly magnetized film, Then TbFe.

Life evaluations were performed on media with anti-oxidation layers formed by sputtering for Tb (Fe8.Go, .>, TbCo), and these will be described below.

In Figure 2, 1.5% square and 1.5mm thick glass substrate are each
A sample of 000 RE-7M film formed by sputtering method was left in a constant temperature and humidity chamber maintained at 70°C and 85% R and H, and was taken out from the constant temperature and humidity chamber at any time to measure the reflectance of the sample. 830 nm from the RE-TMM surface side
These are the life evaluation results obtained by measuring the specular reflectance (relative value to the A.degree. C. vapor deposited film) with respect to the wavelength using Carry-12.

In a magneto-optical recording medium with an RE-7M film as a recording layer, reflected light is used for reproduction, so optical reflectance is an important value. Only the -7M membrane can be considered to have a practical lifetime.

As is clear from FIG. 2, TbCo according to the present invention
The film showed the least decrease in light reflectance among the RE-7M films whose lifetime was evaluated, followed by the (Gdao T bzo ) Co film and the Tb (F
e, o C05o) films followed, and the light reflectance of the Tb (FeSoCo2°) film and TbFe film decreased significantly. Among these, Tb (Feao CO2o) membrane and TbFell were treated at 70°C and 85% R0 for 40 hours and 10 hours, respectively.
After being left in the H6 atmosphere, obvious corroded areas were exposed on the film surface, and it was found that oxidation progressed in the thickness direction of the IC)00 film to the substrate surface side. Figure 3 shows 70℃, 85%R,
This is a photograph showing the metallographic structure of the TbFe film surface after being left in an atmosphere for 10 hours. In this photograph, the branch-like blackened parts were oxidized throughout the film thickness direction as a result of analysis by Auger electron spectroscopy. It has been confirmed that

In this way, in the RE-7M film, TbC according to the present invention
The composition ratio of Co in the O film and the transition metal element is 5.
TbFeC of 0 [at, %1 or more.

Membrane and QC1 lower bco! It will be understood that the lifetime of the RE-TM film layer 14 is much longer than that of the Fe-based film.

The photographs in FIG. 4 are of a TbCo film of 100% square and 1.5L thick on a glass substrate.

TE) (F e a 6 Cot.) membrane, TbFe1
1 by sputtering method, and 10
00 people's 3i3N+! A sample overcoated with an anti-I film by sputtering was heated at 70°C, 85% R,
This figure shows the metal structure of the surface of each sample after being left in a constant temperature and humidity chamber for 100 hours. In Figure 4 (a
) is a TbCo film, (b) is a Tb (Fe, oCo,.)
! , (c) is a TbFe film. While no deterioration was observed in the sample using TbCo film, Tb (
In the samples using the FesoCoto and TbFe films, it is clear that the oxidation of the films significantly progresses from the edges where the Si3N+ overcoat film is insufficiently adhered. Therefore, in order to realize a long-life recording layer on a large-area substrate using an RE-7M film containing Fe as the main transition metal element, it is necessary to form a strong anti-oxidation film without pinholes. It can be determined that it is necessary. As mentioned above, when attempting to implement a practically desirable embodiment in which the recording/reproducing light beam is incident from the substrate surface side and furthermore, a resin material is used as the substrate, it is necessary to R E using Fe as
- It is necessary to interpose a strong anti-oxidation layer with good optical properties and no pinholes between the TMIII and the substrate, and it is assumed that this will be difficult to realize.

11L In Experimental Example 2, the TbCo film according to the present invention, which was concluded from Experimental Example 1 described above to be RE-TMIII that can achieve a practical life, and Tb(Fe<,.Co>,.) Tb(Fe<
g. Co> *・) Clarify the superiority over discipline.

FIG. 5 shows TbCo and Tb (Fes.Co, .) each having a thickness of 1000 mm on a Si substrate with an oxide film.

A sample in which a Tb (Fe, . The sample was placed in a sample holder that can be heated up to 350°C, and the laser beam from the He-Ne laser was converted into linearly polarized light using a polarizer (using a Glan-Thompson prism) and irradiated from the sample film side. The Kerr hysteresis loop of the reflected light was measured through an analyzer (using a Glan-Thompson prism), and the above 3 was derived from the results.
FIG. 3 is a diagram showing the film temperature at which the retention force of RE-TMII of the type becomes 1 [kOe] or less.

In order to realize highly sensitive recording and erasing using a semiconductor laser, the coercive force of the RE-7M film must be several hundred degrees, which can be supplied by a small recording and erasing auxiliary magnet at several hundred degrees Celsius.
It is necessary that it be below [Oe]. For example, the film temperature at which the coercive force decreases to 1 [kOe] or less is a measure of recording sensitivity, and it can be considered that the lower this temperature is, the better the sensitivity is. As is clear from Fig. 5, Tb (FesoCo5o) and Tb (FezoC0
ao> C. Compared to the TbCo film according to the present invention, recording and
The erase temperature is high, and the usefulness of the TbCo film is clear.

Furthermore, the TbCo film according to the present invention, which uses co as the transition metal element in the RE-7M film, is advantageous because ternary alloys are more difficult to manufacture than binary alloys and ternary alloys. .

In Experimental Example 3, co is used as the transition metal, and RE-TMIII, which has a long life and good recording sensitivity, is used for TbCo1! according to the present invention. I and GdCo based on conventional technology
The superiority of the TbCo film according to the present invention will be clarified by comparing the film and the (GdBTl)to)Co film.

Figure 6 shows 1000 TbCo films on 81 substrates,
Results of compositional analysis of GdCo film and (GdsoTbz.)Co film formed by sputtering method and ICPC optical emission spectroscopy,
FIG. 3 is a diagram showing the relationship between film composition and room temperature coercive force Hc derived from the measurement results of Kerr hysteresis loops at room temperature. However, the TbCo film was prepared using a non-bias sputtering method, and the GdCo film and (Gd8°Tb,o)Co
For the film, a bias sputtering method was applied in which a bias of -150 μm was applied to the substrate. This is GdCo
This is because it is difficult to create a perpendicularly magnetized film on the (Gd8°Tb, .)Co film using the non-bias sputtering method.

The magnitude of the coercive force of RE-TMIII at room temperature is required to have a large value of several [kOe] or more in order to ensure the stability of minute bits, but as is clear from Fig. 6, In the case of TbC0 discipline according to the present invention, the composition ratio of Tb in the discipline ranges from 13 [at, %] to
A perpendicularly magnetized film having a coercive force of 2 [kOe] or more can be obtained over a range of 30 [at, %]. On the other hand, (Gd, .Tb
,. ) In the Co film, the composition ratio of (Gds.Tbt.) is ±1.5 around the compensation composition of about 23.5 [at9%].
Only in a narrow compositional region of [at,%], the coercive force is 2
A perpendicular magnetization film of [kOe] or more can be obtained, and GdCo
When it comes to discipline, the compositional ratio of Gd is about 25[a] of the compensation composition.
It can be seen that if t and % deviate, the coercive force is insufficient for practical use. Therefore, the conventional GdC0 film, (G
d. Tb,. ) In Co films, the allowable range of rare earth element composition ratios in which minute recording bits can stably exist is extremely narrow, and the composition must be strictly controlled, including composition uniformity over a large area. There is a problem.

Other problems with G d Co II and (GdTb)Co films (component ratio of Tb in RE is 30at0% or less) can be solved by bias sputtering method (substrate bias voltage is -100V to -200V), as mentioned above. However, it is difficult to obtain a perpendicularly magnetized film unless the magneto-optical disk is used (which is usually the case).However, when using a resin substrate such as acrylic, which is advantageous in terms of cost and ease of forming tracking guide grooves, as a magneto-optical disk. The problem is that the substrate cannot withstand the heat load during the film formation process by bias sputtering.

From these considerations, it is desirable to use <Tb as the rare earth element in the RE-7M film, as in the present invention, taking into consideration the ease of manufacturing compared to the binary system and the ternary system.

As described above, in Experimental Example 1.2.3, TbC0 according to the present invention
II and R E-TM, which has been under development for some time.
The results of a comparative experiment with II are detailed, and the conclusion is that the TbCo film of the present invention has the following advantages: Solve the problem of lifespan. (b) Co
It has high sensitivity compared to a conventional magneto-optical disk whose recording layer is a Tb (FeGO) film containing Co as a main component as a transition metal element and l''e as a transition metal element in addition to Co.

(C) GdCo111, which is a conventional RE-7M film using co as the transition metal element. It has been clarified that GdTbCo film is a highly useful recording layer that solves the problem of difficulty in achieving uniformity over a large area of magneto-optical disks, and is particularly useful for magneto-optical disks and R disks. It has been revealed that this effect is particularly remarkable in magneto-optical disks that use resin materials, which are advantageous in terms of cost, as the substrate material.

Therefore, in the following experimental examples, T b based on the present invention
Focusing on a magneto-optical disk with a Co 11 recording layer, the inventors will specifically explain in detail the results of experiments conducted by the inventors regarding optimization of the composition, film thickness, and disk structure of the recording layer.

11 Gloss Figure 7 shows the TbCo film according to the present invention, in which the compositional ratio of Tb is higher than the compensation composition of about 21 [a [6%]] (hereinafter referred to as Tb-rich film), and in the film with a lower Tb content <
The Kerr hysteretic・This shows the relationship between film coercive force and film temperature derived from the results of measuring the film temperature characteristics of the loop. However, the method for measuring the Kerr hysteresis loop was the same as that used in Experimental Example 2. In Figure 7, each 11
A schematic diagram of the Kerr hysteresis loop at 1 degree is also shown. As shown in the figure, in the case of the Tb-rich film, the loop has a good square shape even when the film temperature increases above 300°C, and the magnetization increases with respect to the externally applied magnetic field (horizontal axis of the Kerr hysteresis loop). The reversal occurs sharply. On the other hand, Co
In the case of a rich film, the squareness of the loop becomes poor in the region where the film temperature is 100°C or higher, magnetization reversal occurs slowly in response to an externally applied magnetic field, and the perpendicular anisotropy is lost in the region where the film temperature is 200°C or higher. cormorant. In order to clarify this situation, in Fig. 7, the external magnetic field at the point where the Kerr rotation angle θ becomes O in the Kerr hysteresis loop is defined as the coercive force HC, and the coercive force HC is required for the Kerr rotation angle θK to reach a constant value. The external magnetic field was defined as HR. Ideally, HC' = HR should hold at any temperature, but while this is ideal in a Tb-rich film, in a Co-rich film, HC < HR significantly when the temperature rises, and the magnetization reversal mechanism is unstable. That will be understood.

FIG. 8 shows the relationship between HC (4HR) and film temperature for samples with various compositions of Tb-rich films. As the composition ratio of Tb increases, Hc≦1
[It can be seen that the film temperature at kOl increases. In other words, it can be determined that a film with a large Tb composition ratio has poor recording sensitivity.

The above was about static evaluation, but next, in order to examine dynamic characteristics, TbCo films with various compositions were formed on acrylic substrates with a diameter of 200 pm and a thickness of 1.5 am. Specifically, X when the compositional formula is expressed as TbxCot-x,
In other words, the composition ratio of Crt) in the TbCo film is x
=15[at, %], 17[at, %], 19[a
t,%], 21[at0%].

23[at, %], 25[at, %], 27[at, %]
at0%], 29[at,%], 31[at0%] 9
Films with different compositions were formed by sputtering to a thickness of 1000 mm, and a SiiNsM prevention film was overcoated thereon by sputtering.

These magneto-optical disks were set in a disk evaluation device using a semiconductor laser with a wavelength of 830n layer as a light source, and the laser power on the film surface was 3 mW to 5 mW, and the strength of the auxiliary magnetic field for erasing on the film surface was 300 [Oe]. ~900 [Oe],
Disc rotation speed 4Crrt/sea, recording frequency 1[M)-IZ],
An attempt was made to form a recording bit under the conditions of a laser beam spot size of #1.5 μm and a diameter of 1.5 μm, and after the bit formation, the bit shape was observed using a polarizing microscope.

As a result, x-15[at,%], 17[at,%],
Regarding the three types of disks with 19 [at, %], the spot size of the laser beam is much larger than that of the laser beam, and magnetization-reversed bits with blurred bit periphery are arranged unstablely (in the laser beam irradiation area). Despite this, it was observed that some parts were not reversed), indicating that a good magnetization reversal bit could not be obtained with a Co-rich film.
This was clarified by this dynamic evaluation. On the other hand, X-23 [at0%], 25 [at,%].

For the four types of disks, 27[at,%] and 29[at0%1, l! It was noticed. Among these four types, x=23
The bit shape of the film [at,%] is closest to the laser beam spot size (slightly smaller than the spot size)
, dynamic evaluation also revealed that as X increases, the magnetization reversal bit tends to become smaller, and as X increases, recording sensitivity deteriorates. Also, X=21[at,
%], the room-temperature coercive force was larger than the maximum magnetic field of 12 [kOl] that can be generated by the magnetizing device used by the inventors, so it was impossible to magnetize the disk. It was found that the bit shape itself was good and that it was suitable for practical use as long as the magnetic field generated by the magnetizing device was sufficient.

Regarding the remaining disk with X'''31 [at, %], it was difficult to form bits even under the conditions of a laser power of 5 mW and a recording magnetic field of 900 [Oe]. That is, this x-
It was found that the recording threshold value of the disk with 31 [at, %] was too high to be practical.

As mentioned above, from the results of Experimental Example 4, in order to form by irradiating a low power laser beam from a semiconductor laser etc. and applying an auxiliary magnetic field of several hundred [○e], the compositional ratio of Tb in TbCo11 must be 21 [at, %] ~ 30 [a
t,%].

The compositional component ratio of Tb is 21 [at, %] to 30 [
at8%], the thickness of the TbCo film is 10%.
As described in Experimental Example 4, in the case of 00 people, the size of the recording bit is smaller than the spot size of the recording laser beam. The reproduction laser beam spot is usually the same as the recording laser beam spot size, so if the recording bit size is small, the C/N during reproduction will be lower.
decrease.

Therefore, the inventors created a film (21at, %≦X≦30at1%
) in an attempt to increase the spot temperature of the recording film in the area irradiated with the recording laser beam. The results of basic experiments conducted by the inventors prior to the recording test will be described in advance.

FIG. 9 shows a film of TbxCot-X having a composition of x-25 [at 1%] on a glass substrate, exposed to 50 and 100 people.

Reflectance from the substrate side, transmittance (measured with Carry-14), and Kerr rotation at room temperature of each sample formed by sputtering with 7 types of film thickness of 200, 300, 500, and 800. This figure shows the relationship between the size of the angle and the film thickness. Among these quantities, the reflectance and the magnitude of the Kerr rotation angle are quantities directly related to the C/N of the reproduced signal, and it is desirable that both of them be as large as possible. However, as can be seen from Fig. 9, the reflectance and the Kerr rotation angle decrease significantly in the region of film thickness of 500 Å or less, and at the same time, it is impossible to form a TbCo film with poor reproducibility, especially at a film thickness of 50 Å. Therefore, the error par of the car rotation angle is large. This is common to all RE-TMII, but the magneto-optical properties of the TbCo film are sensitive to the surface condition of the underlayer, so if the film is thin, it is likely to be affected by the interface of the underlayer. This is caused by

Next, Tt)
-X films with various thicknesses and compositions were formed by sputtering, and 5isN41! Fabricate a magneto-optical disk overcoated with A by sputtering method,
Recording, playback, and erasing tests were conducted using the same disk evaluation device as described in Experimental Example 4. The recording characteristics are determined by the recording threshold power (defined as the power per recording laser when the recording bit diameter is 1.5 μm or more) when the recording auxiliary magnetic field is kept constant at 400 [Oe], and the magnetization reversal bit shape determined by a polarizing microscope. The reproduction characteristics were evaluated by observation of 1mW of power on the film surface.

A semiconductor laser beam with a wavelength of 830 rv was continuously irradiated onto the track where recorded bits were formed, and evaluation was made from the main signal reproduction peak intensity. However, the linear velocity of the beam (relative velocity between the beam and the disk) was 4 m/sec, and the auxiliary magnetic field used during reproduction was 0 [Oe]. The erasing characteristics were evaluated by performing a reproduction test on the same part of the erasing test mock and observing the main signal reproduction peak intensity and the disc after erasing with a polarizing microscope. However, for erasing, a laser beam was applied to the film surface at a power of 5 mW and a wavelength of 830 nll.

Continuously irradiate onto the track where the recording bit string exists at a linear velocity of 4 m/Sec, and at the same time, 400 m/sec in the opposite direction to that during recording.
This was done by applying an auxiliary erasing magnetic field of [Oe].

For the dynamic characteristic evaluation described above, change the X of TbxCo+, -x to
= 21 [at, %] to 30 [at, %], and the TbCo film thickness was changed to 4 types, between 100 and 800 people. As a result, the recording/erasing characteristics were as follows. When the thickness of the T bx Co+-x film was 400 Å or less, it was good over the composition range of 21 [at, %]≦X≦30 [at, %]. From the viewpoint of playback characteristics, the film thickness is 400
In the region of Å or less, the thicker the film is, the better it is, and in the case of a film thickness of 50 nm, the reproduced signal is inherently unstable. Compatible. In the region where the film thickness was 500 Å or more, the reproduced signal peak decreased particularly in the range where X was large. This is because the diameter of the magnetization reversal bit is smaller than the spot size of the recording laser beam (=the spot size of the reproducing laser beam). Note that for the x-21 [a 0%] sample, as described in Experimental Example 4, the reproduction characteristics were not evaluated due to the performance of the magnetizing device.

From the results of Experimental Example 5 above, it can be seen that the thickness of the recording layer made of the TbCo film according to the present invention is desirably 100 Å or more and 400 Å or less.

Support 11L From the test results of a magneto-optical disk in which a TbCo film as a recording layer was directly formed on a substrate and a transparent 5iaN+ film was provided thereon (Experimental Example 4.5), X of the TbXC0+-X film was 21. [at, %] to 30 [at, %], and the thickness of the TbCo film is preferably 100 Å to 400 A, but as described in Experimental Example 5, by specifying the film thickness, recording and Although the erasing characteristics were improved, some problems remained in the reproduction characteristics. In this Experimental Example 6, an attempt was made to optimize the structure of the magneto-optical disk in order to improve this problem.

Conventionally, in magneto-optical disks with RE-TMIII as the recording layer, a multiple interference layer is laminated with RE-TMI for the purpose of improving the C/N of the reproduced signal, so that the apparent Kerr rotation angle θ is Attempts have been made to increase the value of θ by optimizing the model structure.
! ! It has been reported that it is 3 to 4 times larger than in the case of . Here, the reproduction C/N is an amount proportional to the product of the light reflectance R on the film surface of the disk, the Kerr rotation angle θ, and the power 1o of the reproduction laser beam. When a PIN diode is used as a photodetector for reproduction, this relationship is described as C/Na:Ia -R.0g.'' (1).

By providing multiple interference layers, it is true that θ in equation (1) increases significantly, but the apparent increase in θ in equation (1) due to the structure with multiple interference layers increases at the same time. It is inevitable that this will result in a decrease in R. Therefore, it is desirable to increase the power Ia of the reproduction laser beam in order to directly reflect the enhancement effect on θ due to the multiple interference layer in an increase in reproduction C/N. However, for example, RE-TM in which Fe is the main component of the transition metal element
In conventional magneto-optical disks with II as the recording layer,
When the power of the laser beam for reproduction is increased, the m during reproduction increases.
Since the magnitude of θ significantly decreases due to temperature rise, no significant improvement in reproduction C/N could be expected even if multiple interference layers were provided.

FIG. 10 shows 'rbcol!' according to the present invention. JI's I! The relationship between film temperature and Kerr rotation angle for conventional TbFe film.

It is shown in comparison with T b (F e,, Co,, ) discipline. The sample was formed by sputtering each RE-TMIII to a thickness of 1000 mm on a 3i substrate with a thermal oxide film, and then 3i3N+! A protective layer made of II is formed by a sputtering method,
FIG. 10 shows the results of measuring the temperature characteristics of the Kerr hysteresis loop for each of these samples using the method described in Experimental Example 2. As is clear from FIG. 10, in the case of the TbCo film according to the present invention, even if the film temperature increases, the Kerr rotation angle decreases as compared to the conventional T b F em.

It can be seen that the reproduction C/N can be effectively improved by the structure having multiple interference layers, which is much smaller than the T b (F ess Cots > film).

Based on the above findings, a diameter of 200 ru and a thickness of 1.5
On an acrylic substrate of
A film was formed to a thickness of 0.00 mm, and on top of that a film was formed to a thickness of 250 mm, and the composition ratio of Tb was 25 [at.

%] TbCo film was formed, and 3i
A magneto-optical disk on which a 3N+ sputtered film was deposited to a large extent was fabricated as a prototype, and its dynamic characteristics were evaluated.

The recording conditions were a laser beam power of 5 mW on the film surface.

Recording magnetic field 400[Oe], disk rotation speed 4m/
The linear velocity was kept constant at sec. In addition, as playback conditions, the power of the laser beam was 0.5 mW and 1 mW.

When the reproduced signal peak intensity was examined by changing the power to 1.5 mW, 2 mW, and 2.5 mW, it was found that the reproduced signal peak intensity when the reproducing laser beam power was 1 mW was the same as the interference when recording and reproducing under the same conditions. It increased by 2.5 times compared to the disk without the layer (81aN41!! between the substrate and the TbCo film). At the same time, the peak intensity of the reproduced signal increased almost in proportion to the reproduction laser beam power. Therefore, ,Tb
It was confirmed that Co11l is an excellent material for the recording layer, also in taking advantage of the effect of the multiple interference layer.

In addition, for the purpose of further increasing the reproduction signal, TbC0W
In order to effectively use the laser beam for reproducing the recording layer consisting of II, a magneto-optical disk having a four-layer film structure as shown in FIG. 1 was fabricated as a prototype. Note that the relationship between the thickness of the TbCo film and the light transmittance is as explained in FIG. 9.

That is, in FIG. 1, the substrate 1 is an acrylic plate with a guide groove having a diameter of 200 mm and a thickness of 1.5 m, and the first and second interference layers 2.4 each have a thickness of 1100 mm and a light transmittance. A 3i3N+ sputtered film with a refractive index of approximately 95% (at a wavelength of 830 nm) and approximately 1.9 was formed, and the recording layer 3 had a film thickness of 250 nm and a Tb composition ratio of 25.
[at.

%] of TbCo sputtered film, and further a light reflecting film 5
An A°C film with a thickness of 600 mm was formed as follows.

The magneto-optical disk with this configuration was subjected to dynamic characteristic evaluation, and the recording bit string was formed using a recording laser beam power of 5 mW, a recording magnetic field of 4000 [○e], and a disk rotation speed of 4 m/s.
ee, the recording frequency was 1 MH2, the laser beam spot size was 1.5 μm, and reproduction was performed by continuous irradiation with a 1 mW reproduction laser beam. The layer is added 1.5 times that of A42 (without reflective layer) to achieve the practically required C/N (for example, 5 with IMH2).
It was confirmed that the value significantly exceeds 0 dB>.

As a light reflecting layer, in addition to the above-mentioned Al1, AQ, Cu.

When a similar test was conducted using AU and N+ protection, the Ao, Cu, and Au films, which had a light reflectance of 80% or more at a wavelength of 830 na+, obtained similar results to the A2 film. , N1 with a light reflectance of less than 80%
In the case of membranes, almost no effect was seen with the four-layer structure. Therefore, the light reflecting layer preferably has a reflectance of 80% or more with respect to the wavelength of the reproducing laser beam.

As described above, based on the present invention, the compositional component ratio of Tb is <21[
at, %] to 30 [at0%], and the film thickness is preferably in the range of 100 to 400.
In the magneto-optical disk according to the present invention having a film as the recording layer, providing an interference layer to increase the Kerr rotation angle is effective in increasing the reproduction C/N. Moreover, this interference layer is made of TbC and the substrate.

Just placing one layer between the recording layer and the recording layer has a sufficient effect, and by actively utilizing the light that passes through the recording layer,
On the surface of the TbC0 recording layer opposite to the substrate surface, there is an interference layer and a light reflection layer that are transparent to the wavelength of the recording/reproducing laser beam (as mentioned above, these also function as a protective layer).
Even greater effects can be expected by stacking them.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the structure of a magneto-optical disk according to an embodiment of the present invention, and Fig. 2 shows the results of life evaluation based on optical reflectance of magneto-optical disks having various RE-TM films as recording layers. Figure 3 shows the recording layer of a conventional magneto-optical disk.
Micrographs showing the metallographic structure of the surface after the corrosion resistance test of bFe1ll, Figures 4(a) to (C) are respectively Tb
A micrograph showing the metallographic structure of the surface after a corrosion resistance test of a magneto-optical disk using a Co11°Tb (Fe8.Co2°) film and a TbFe film as a recording layer, FIG. 5 is a TbCo film. T b (F e,. Co,.) III, T b (F
C20Co,. ) A diagram showing the film temperature at which the coercive force of a magneto-optical disk with a hood as a recording layer becomes 1 [Oe] or less. GdCo111. (Gd,.Tb,.)C. Figure 7 shows the relationship between the film composition component ratio and room temperature coercive force of the recording layer of a magneto-optical disk using a film as the recording layer. Figure 8 shows the relationship between the film temperature of the recording layer of a magneto-optical disk and the coercive force and the external magnetic field strength for obtaining saturated Kerr rotation. A diagram showing the relationship with coercive force, Figure 9 is T
A diagram showing the relationship between the TbCo film thickness, reflectance, transmittance, and Kerr rotation angle of a magneto-optical disk having a bCo film as a recording layer,
FIG. 10 is a diagram showing the relationship between the film temperature and the Kerr rotation angle of a magneto-optical disk in which a TbFe film and a TbFeCo film are used as recording layers. 1...substrate, 2...first Interference layer, 3... Recording layer, 4... Second interference layer, 5... Light reflecting layer, 6...
protective layer. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 8 Figure 2 Figure 5 Figure 6

Claims (5)

[Claims] (1) A substrate, a recording layer formed on this substrate and made of a rare earth-transition metal amorphous alloy thin film having an axis of easy magnetization in a direction perpendicular to the substrate surface, and the substrate surface of this recording layer. In the magneto-optical disk comprising a protective layer formed on the opposite side, the rare earth element in the recording layer is Tb.
, the transition metal element is Co, and the composition ratio of Tb in the recording layer is 21 [at. %] to 30[at.
%]. (2) The thickness of the recording layer is 100 [Å] or more, 400 [Å] or more
3. The magneto-optical disk according to claim 1, wherein the magneto-optical disk has a diameter of less than 1 Å. (3) An interference layer made of a transparent material with respect to the wavelength of the recording/reproducing light beam is provided between the substrate and the recording layer. magneto-optical disk. (4) an interference layer in which the protective layer is made of a material that is transparent with respect to the wavelength of the recording/reproducing light beam; and an interference layer formed on the surface of the interference layer opposite to the recording layer; Claim 1, characterized by comprising a reflective layer having a reflectance of [%] or more;
The magneto-optical disk according to item 2 or 3. (5) A magneto-optical disk according to claim 1, 2, 3 or 4, wherein the substrate is made of a resin material.