JPH0562835A - Magneto-optical recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium wherein a bismuth- substituted garnet film can be obtained at low costs and easily by using a sputtering method by a method wherein a substratum layer provided with a garnet structure is formed on a glass substrate and a recording layer composed of a bismuth-substituted garnet is formed on the substratum layer. CONSTITUTION:An amorphous layer as a derivative of YIG (yttrium iron garnet Y3Fe502) is formed, by a sputtering method, on a borosilicate glass substrate 1 composed of an alkaline-free metal glass. It is heat-treated at a temperature of 700 deg.C or lower. A substratum layer 2 composed of a crystalline YIG film is formed. A recording film 3 composed of a bismuth-substituted garnet film (Bi2DyGa0.8Fe4.2O12) is formed on the substratum layer 2 by a sputtering method at a substrate temperature of 550 deg.C. Crystals constituting the recording film 3 by a polycrystalline film are constituted of dense column-shaped fine crystals 4, and this structure is completely the same as a film which has been made crystalline during the formaiton operation of a film on a GGG substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium and a method for manufacturing the same, and more particularly to a magneto-optical recording medium in which a glass substrate is used as a substrate and a bismuth-substituted garnet film is formed as a recording film thereon by a sputtering method. The manufacturing method is related.

[0002]

2. Description of the Related Art A bismuth-substituted garnet film formed by a sputtering method has a large Faraday rotation angle and a perpendicular magnetic characteristic with a large coercive force and squareness ratio. Recently, it has attracted attention as a high-density magneto-optical recording medium for magnetic recording.

By the way, as a substrate for sputtering a bismuth-substituted garnet film formed by this sputtering method, a single crystal gadolinium gallium garnet (GGG; Gd ₃ Ga ₅ O ₁₂ ) substrate conventionally formed by the Czochralski method or A glass substrate having high heat resistance has been used.

When a bismuth-substituted garnet film is formed on such a single crystal GGG substrate at a high temperature,
A film equivalent to a single crystal is formed, and such a bismuth-substituted garnet film produces little medium noise, and good recording / reproducing characteristics can be obtained. However, this single-crystal GGG substrate is expensive because it requires an extremely high-purity raw material, and therefore has a drawback that the manufacturing cost of the magneto-optical recording medium to be formed is large and it is not practical.

On the other hand, when a bismuth-substituted garnet film is formed on a glass substrate, an amorphous film which is a derivative of the bismuth-substituted garnet film is first formed and then crystallized by heat treatment. The way to do is taken.

However, in the case of crystallization by this heat treatment, a polycrystalline film having no dominant orientation is formed, the crystal grains constituting this polycrystalline film become large, and the crystal grain boundaries are remarkably formed. Therefore, when this is used as a magneto-optical recording medium, light scattering occurs, and when recording / reproducing, a large medium noise occurs.

As in the case of using a GGG substrate, if it is possible to crystallize during film formation, it is expected that crystal grain boundaries will not be significantly formed and medium noise will be reduced. A technique for directly crystallizing a bismuth-substituted garnet film during deposition has not been established so far.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a magneto-optical recording medium in which a crystallized bismuth-substituted garnet film with low medium noise can be formed on an inexpensive glass substrate, and its manufacture. The purpose is to provide a method.

[0009]

The magneto-optical recording medium of the present invention is characterized in that an underlayer having a garnet structure is provided on a glass substrate, and a recording film made of bismuth-substituted garnet is provided on the underlayer. To do.

Further, the recording film made of the bismuth-substituted garnet is characterized by being formed by a high temperature film forming method in which the film is crystallized during film formation by a sputtering method. Further, the bismuth-substituted garnet film has a general formula of Bi _x R _3-x M _Y Fe _5-Y O
₁₂ (O ≦ X ≦ 3, 0 ≦ Y <2), R is yttrium or at least one element selected from rare earth elements, and A is an element capable of substituting with iron element. Is characterized in that

Further, the underlayer has a general formula of A _x R _3-x M _Y
Fe _5-Y O ₁₂ (O ≦ X <1, 0 ≦ Y <5), A represents bismuth or a lead element, and R represents at least yttrium or an element selected from rare earth elements. One element, and M is an element capable of substituting for iron element.

Further, the glass substrate is borosilicate glass containing no alkali metal. Further, in the method of manufacturing a magneto-optical recording medium of the present invention, after forming an amorphous film which is a derivative of a garnet structure on a glass substrate by a sputtering method, the substrate is heat-treated at a temperature of 700 ° C. or less to obtain the amorphous film. Characterized in that a crystalline film is crystallized to form an underlayer, and a polycrystalline film of a bismuth-substituted garnet film is formed on the crystallized underlayer by a sputtering method by a high-temperature film-forming method for crystallizing during film formation. It is what

[0013]

When the amorphous bismuth-substituted garnet film formed on the glass substrate is crystallized by the heat treatment, the crystal grains become large and the grain boundaries are remarkably formed. This tendency reduces the substitution amount of bismuth. Alternatively, when the bismuth is not contained at all, a good garnet film is formed even if crystallization is performed by heat treatment.

Therefore, a good bismuth substitution is achieved by crystallizing a thin garnet film which does not contain bismuth on the glass substrate or which is substituted with bismuth to some extent, and then crystallizing a garnet film having a large amount of bismuth substitution during film formation. A garnet film is obtained.

Therefore, it is necessary to crystallize a garnet structure thin film containing no bismuth or having a small amount of bismuth substitution on the glass substrate. by the way,
When an amorphous film formed by sputtering is crystallized by heat treatment, the crystallization temperature depends on the bismuth substitution amount.

When the bismuth-substituted garnet film per one molecular formula contains about 2 bismuth atoms, the crystallization temperature is 650 ° C., but the garnet film containing no bismuth atoms has a crystallization temperature of 700 ° C. or more. During this period, the crystallization temperature decreases substantially in proportion to the amount of bismuth substitution.

When the glass used as the substrate material is a borosilicate glass containing no alkali metal, it has high heat resistance, but it is still softened by heat treatment at a temperature of 700 ° C. or higher for a long time (several tens of minutes or longer). .. Therefore, when an amorphous film containing no bismuth atoms is heat-treated in an ordinary electric heating furnace to be crystallized, diffusion occurs between the amorphous film and the glass substrate, and a crystallized recording film is not formed. Remarkable unevenness is generated, which makes it unsuitable as a base film.

Therefore, when crystallizing this amorphous film, it is effective to rapidly heat the substrate to crystallize it by using an infrared lamp or the like. According to this method, crystallization can be performed quickly, so that softening of the glass of the substrate and diffusion between the amorphous film and the substrate are suppressed, and a good crystalline film can be obtained.

On the underlayer made of the YIG film crystallized in this way, the applicant of the present invention previously disclosed in Japanese Patent Laid-Open No. 2-239448.
The bismuth-substituted garnet film was formed by the method of crystallization during film formation by the sputtering method of the high temperature film formation method disclosed in No.

By doing so, a magneto-optical recording medium having a magneto-optical recording characteristic similar to that when a single crystal GGG substrate is used as a sputtering substrate can be formed, a Faraday rotation angle is large, and a coercive force, It was confirmed that a magneto-optical recording medium exhibiting a perpendicular magnetic characteristic having a large squareness ratio can be easily obtained at low cost.

[0021]

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1 (a), the borosilicate glass substrate 1 made of non-alkali metal glass has
In the general formula A _x R _3-x M _Y Fe _5-Y O _{12 represented} by,
YIG when x = 0, Y = 0 and R is yttrium
An amorphous film, which is a derivative of (yttrium iron garnet, Y ₃ Fe ₅ O ₁₂ ), was formed by the sputtering method, and this was 700 ° C.
Crystallized by being heat-treated at the following temperature, crystalline YIG
A base layer 2 made of a film is formed.

A Bi _x R _3-x M _Y Fe _5-Y O ₁₂ (0 ≦ x) of the general formula expressed in claim 3 is formed on the underlayer 2 by a sputtering method at a substrate temperature of 550 ° C. ≤3, 0 ≤ Y <2), x = 2, R is dysprosium (Dy), Ga element that can replace M with iron element, and bismuth-substituted garnet film with Y = 0.8 (Bi ₂ DyGa _0.8 Fe _4.2 A recording film 3 made of O ₁₂ ) is formed. The bismuth-substituted garnet film thus formed was a polycrystalline film having no dominant orientation when inspected using an X-ray diffraction method.

Further, as shown in FIG. 1 (b), the crystal forming the recording film 3 of the polycrystalline film is composed of dense columnar (columnar) microcrystals 4, and this structure is formed on the GGG substrate. It is exactly the same as the film crystallized during film formation. Therefore, the light scattering is very small, and the recording film has excellent magneto-optical recording characteristics.

The recording film 3 is made of a conventional single crystal GG.
High-temperature film formation can be performed at the same temperature as when the G substrate is used as a substrate for sputtering. When the surface of this recording film 3 is observed by a 400 × differential interference microscope, the surface is smooth like the YIG film of the underlying layer. In addition, a high-quality recording film in which the presence of crystal grains was hardly seen was obtained.

When the Faraday hysteresis loop of the magneto-optical recording medium having the structure of the glass / YIG / bismuth-substituted garnet film of the present invention was measured, the squareness ratio was 1 and the coercive force was 2 KOe as shown in FIG. A perpendicular magnetic film was obtained.

This value was similar to that of a magneto-optical recording medium formed by a conventional method in which a bismuth-substituted garnet film was crystallized directly during film formation on a single crystal GGG substrate.

A method of manufacturing such a magneto-optical recording medium of the present invention will be described. Borosilicate glass containing no alkali metal as described above (HOYA Co., Ltd., trade name; NA-40, Asahi Glass Co., Ltd., trade name; AN, Corning Co., trade name; 7
(059)), a high frequency magnetron sputtering method is used, and argon (Ar) gas is used as a sputtering gas at a substrate temperature of 300 ° C. to obtain a YIG (yttrium iron garnet, Y ₃ Fe ₅ O ₁₂ ) derivative. To form an amorphous material having a thickness of 0.1 μm.

In this case, the above-mentioned alkali-free metal borosilicate glass has a high softening point of about 700 ° C., is resistant to the temperature for crystallizing the above-mentioned underlayer, and has a thermal expansion coefficient of 5 × 10 ^−6.
Since it is as high as / ° C and is close to the YIG film, cracks do not occur when the YIG film is cooled after heat treatment.

Since the coefficient of thermal expansion of quartz glass is too different from that of the YIG film, cracks and the like are generated when the YIG film is cooled after heat treatment, which is not suitable. Then, the glass substrate 1 provided with this amorphous film is heated in a nitrogen gas atmosphere at a temperature rising rate of 10 ° C./sec to a maximum attainable temperature of 700 ° C., held at this temperature for 2 minutes, and then rapidly cooled with nitrogen gas. Then, the amorphous film was crystallized to form the underlayer 2.

As a heating means for the heat treatment of the underlayer,
An infrared lamp was used to rapidly raise the temperature of the substrate, and the substrate was placed on a carbon susceptor to enhance the infrared absorption efficiency and prevent the glass substrate from softening.

When the crystallized underlayer YIG film was inspected by an X-ray diffraction method, YIG was crystallized in a single phase and no heterogeneous phase was observed. Further, the surface of the YIG film was observed with a 400 × differential interference microscope, and the surface was smooth.

Next, the glass substrate 1 on which the underlayer 2 is formed is kept at a temperature of 550 ° C., and a recording film 3 made of a bismuth-substituted garnet film as a recording film is formed on the substrate 1 by a high frequency magnetron sputtering method. did. The recording film 3 made of this bismuth-substituted garnet film was formed by the method previously disclosed by the present inventor in Japanese Patent Laid-Open No. 2-239448.

That is, the apparent composition of the target was Bi ₂ DyGa _0.7 by the high frequency bipolar magnetron sputtering method.
Films were formed at a gas pressure of 1 Pa by using Fe _4.3 O ₁₂ as the sputtering gas and argon gas containing 10% by volume of oxygen gas as the sputtering gas.

By doing so, a magneto-optical recording medium similar to the magneto-optical recording medium formed by the conventional method in which the bismuth-substituted garnet film is crystallized directly during deposition on the single crystal GGG substrate. Was obtained.

[0035] Instead of the addition to the bismuth-substituted garnet film as a recording film of this example _{(Bi 2 DyGa 0.8 Fe 4 .2} O 12),
A bismuth-substituted garnet film having a composition of Bi ₂ DyGaFe ₄ O ₁₂ may be used, and Y ₃ Ga ₂ Fe ₃ O ₁₂ may be used instead of a YIG (yttrium iron garnet, Y ₃ Fe ₅ O ₁₂ ) film as an underlayer.
Yttrium gallium iron garnet film such as YI
A RIG film (R is a rare earth element) in which yttrium, which is a rare earth element of the G film, is replaced with another rare earth element may be used.

[0036]

As described above, according to the present invention, it is possible to obtain a magneto-optical recording medium of bismuth-substituted garnet which has good recording / reproducing characteristics and is low in manufacturing cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium of the present invention.

FIG. 2 is a characteristic diagram of the magneto-optical recording medium of the present invention.

[Explanation of symbols]

 1 Borosilicate glass substrate 2 Underlayer 3 Recording film 4 Column-shaped microcrystal

Claims (6)

[Claims] 1. An underlayer (2) having a garnet structure is provided on a glass substrate (1), and a recording film (3) made of bismuth-substituted garnet is provided on the underlayer (2). Magneto-optical recording medium. 2. A magneto-optical recording medium, characterized in that the recording film (3) made of the bismuth-substituted garnet according to claim 1 is formed by a high temperature film forming method in which crystallization occurs during film formation by a sputtering method. .. 3. The bismuth-substituted garnet film of the recording film (3) according to claim 1, wherein the bismuth-substituted garnet film has a general formula of Bi _x R _3-x M _Y Fe _5-Y O ₁₂ (O
≦ X ≦ 3, 0 ≦ Y <2), and R is at least yttrium or an element selected from rare earth elements.
1. A magneto-optical recording medium, characterized in that one element can be replaced with M, and the element M can be replaced with an iron element. 4. The underlayer (2) according to claim 1, wherein
A _x R _3-x M _Y Fe _5-Y O ₁₂ (O ≦ X <1, 0 ≦ Y <5), A is bismuth or lead element, R is yttrium or rare earth element A magneto-optical recording medium, wherein at least one element selected from the more selected elements and M is an element capable of substituting with an iron element. 5. A magneto-optical recording medium, wherein the glass substrate (1) according to claim 1 is a borosilicate glass containing no alkali metal. 6. A glass substrate (1) is formed with an amorphous film, which is a derivative of a garnet structure, on a glass substrate (1) by a sputtering method, and then the substrate is treated with 70
Heat treatment at a temperature of 0 ° C. or lower to crystallize the amorphous film,
A recording film (3) made of a bismuth-substituted garnet film is formed on the crystallized underlayer (2) by using a sputtering method and a high-temperature film-forming method in which the film is crystallized during film formation. Manufacturing method of magnetic recording medium.