JPH06302432A - Garnet polycrystalline film for optical magnetic recording medium, optical magnetic recording medium and optical magnetic recording disk - Google Patents

Abstract

PURPOSE:To form a high-performance optical magnetic recording medium on an inexpensive substrate by stacking polycrystalline garnets by two or more layers at least, and besides, constituting the crystalline lattice constant between adjacent garnet layers so as to be different at a specified ratio or more. CONSTITUTION:This is a polycrystalline garnet represented by the composition of BixR3-x+uMyFe5+y+vO12 (0<=x<=3, 0<=y<=5, -3<=u<=3, -5<=v<=5, R shows one or more kinds of rare earth elements including yttrium, and M a trivalent metal replaceable with iron). This is a garnet polycrystalline two-layer film for an optical magnetic recording medium, which consists of two layers whose crystal lattice constant is different by + or -0.3% or more, and in which the average grain diameter of the garnet polycrystalline second layer made on the first layer is smaller than that of the first layer on a glass substrate, and besides is 1mum or under. Hereby, a polycrystalline garnet film consisting of fine crystal particles can be formed on an inexpensive substrate, and a high-performance polycrystalline optical magnetic recording medium can be obtained, using it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine crystal grain garnet polycrystalline film effective for reducing noise originating from grain boundaries in a garnet polycrystalline magneto-optical recording medium and its application.

[0002]

2. Description of the Related Art Garnet type oxides are materials exhibiting excellent performance as recording materials such as magneto-optical recording media, optical isolators, current / magnetic field sensors or magneto-optical devices. In general, this material is non-magnetic in the amorphous state and is therefore used in the single crystal or polycrystal state.
However, the polycrystalline garnet that can be manufactured at low cost is
Compared with single crystal garnet, it has optical properties such as grain boundaries,
Poor magnetic or magneto-optical properties. In particular, for application as a magneto-optical recording medium, it is essential to improve the performance of polycrystalline garnet.

Magneto-optical recording is the most effective technique for achieving high density and high reliability. Garnet material, which has high corrosion resistance and large magneto-optical effect at short wavelength, is a next-generation magneto-optical medium that can overcome the drawbacks (low corrosion resistance and small magneto-optical effect) of amorphous rare earth-transition metals that have already been realized. Most promising. As a method of further improving the recording density, multi-layer recording using a multi-layer film utilizing the translucency of garnet has been proposed (Ito et al .: Proc. 10th Annual Meeting of the Japan Society for Applied Magnetics, 31 (198).
6)).

Further, if the garnet film is combined with a conventional amorphous transition metal rare earth alloy or another metal-based magneto-optical recording medium such as a Pt or Pd / Co multilayer film, the magnetic field utilizing the large Faraday rotation angle is used. It is known that the optical effect can be enhanced and it is effective for improving the performance of the magneto-optical recording medium. The Bi-substituted garnet film formed on a GGG (gallium gadolinium garnet) single crystal substrate exhibits a high performance of 60 dB in terms of carrier / noise ratio (signal / noise ratio under standard conditions) in recording / reproducing characteristics (H. Kano etal: IEEE Trans. Magn. MAG-25 (5), 3737
(1989)). However, in the case of a garnet film formed on an inexpensive glass substrate or the like, it is polycrystalline and has a large medium noise due to optical nonuniformity (nonuniform distribution of refractive index) derived from crystal grain boundaries. There is.

In order to form a high-performance polycrystalline garnet film on a glass substrate or the like, grain refinement is effective in reducing optical nonuniformity caused by grain boundaries (eg, M. Abe an.
d M.Gomi; J. Magn. Magn. Mater., 84, 222 (1990)
). Additive elements (for example, Ito et al .; Proc.
127 (1989)), or rapid (heat treatment) crystallization method (T. Suzuki et al; 13th Applied Magnetics Society Academic Lecture Summary, 49 (1989)).

[0006] Shono conducted a transmission electron microscope observation after the complete crystallization of the garnet film and found that the lattice constant differs by about 1%.
Fine crystal grains are observed in the garnet film formed on the G single crystal (111) plane, but the lattice constant is different by about 0.3%, and the GCGMM (calcium, magnesium, zirconium-substituted gadolinium gallium garnet) single crystal substrate It has been reported that no fine crystal grains are observed above, and that epitaxial growth occurs (Shono; "Light and magnetism-its basics and applications-", 1988 Applied Magnetics Seminar text,
107 (1988)).

The present inventors have found that Bi and Ga having a garnet structure after crystallization on a GGG single crystal substrate having various plane orientations.
An amorphous film of substituted DyFe garnet was prepared, the crystallization process by heat treatment was observed in detail, and the crystal lattice constant was ±
It was confirmed that garnet oriented fine crystal grains were preferentially generated inside the amorphous film or on the surface of the amorphous film from the interface with the single crystal substrate different by 0.3% or more. This means that at the interface between the amorphous film having a garnet structure after crystallization and the garnet single crystal, the increase in the interface energy due to the formation of crystal nuclei is larger than that in the inside of the amorphous film or the surface not in contact with the garnet single crystal. It is small, and it is considered that heterogeneous nucleation in this part occurs preferentially.
Further, it is considered that the epitaxial growth is hindered due to the misfit of the lattice constant, and the single crystal film in the strict sense is not formed even on the single crystal substrate, and it becomes oriented microcrystals.

[0008]

SUMMARY OF THE INVENTION The present invention provides a high performance polycrystalline magneto-optical recording medium by realizing a polycrystalline garnet film consisting of fine crystal grains on an inexpensive substrate and applying it. The purpose is to

[0009]

The present invention is a polycrystalline garnet film formed of fine crystal grains formed on a substrate, and a high-performance magneto-optical recording medium to which the same is applied. Here, the substrate includes a substrate made of an amorphous material such as glass, a polycrystalline material including garnet, and a single crystalline material including garnet.

Rare earth iron garnet has a basic composition of R ₃ F.
e ₅ O ₁₂ (wherein, R is a rare earth element including yttrium) is represented, in the present invention, R to _{Bi, Bi x R 3-x} M y Fe 5 by substituting Fe with metals such as Ga _-y O
_A magneto-optical recording medium having a composition of ₁₂ (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 5, R is at least one rare earth element including yttrium, and M is a trivalent metal that can replace iron). Mainly used as.

However, in the case of a thin film produced by the sputtering method, Bi _x R _{3−x + u} M _y Fe deviated from the above composition.
_{5-y + v} O ₁₂ (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 5, −3 ≦
u ≦ 3, −5 ≦ v ≦ 5, R is one or more kinds of rare earth elements including yttrium, and M is a trivalent metal substituting for iron), and polycrystalline garnet is obtained. It is known that However, when u = 0 and v = 0, garnet is obtained in a single phase, and the recording / reproducing characteristics are usually highest. -0.3≤u≤0.3, and -0.5≤v≤
If it is 0.5, a compound phase other than garnet and an amorphous phase (both of which are called “different phase”) are not clearly confirmed, but there is a possibility that they are generated. u ≠ 0,
Alternatively, the composition with v ≠ 0 may have the highest recording / reproducing characteristics. -1.0≤u≤1.0, and -1.7≤v≤
1.7, -0.3≤u≤0.3, and -0.5≤v≤
If it is not included in 0.5, generation of a hetero phase is confirmed.
Therefore, the recording / reproducing characteristics may deteriorate, but the recording / reproducing characteristics may be high. Furthermore, −3.0 ≦ u ≦
3.0 and -5.0≤v≤5.0, -1.0≤u≤
When 1.0 and -1.7≤v≤1.7 are not included, -1.0≤u≤1.0 and -1.7≤v≤1.7.
, -0.3≤u≤0.3, and -0.5≤v≤0.5
More than if it is not included in the
In many cases, the recording / reproducing characteristics deteriorate. It is known that a metastable phase having a composition of u ≠ 0 or v ≠ 0 can be obtained in a garnet thin film, and even in the above cases and when a metastable phase is obtained, a different phase from that of garnet polycrystal is obtained. In some cases, a mixture with and is produced (hereinafter, referred to as "polycrystalline garnet" including the latter case).

In order to realize a polycrystalline garnet having a crystal grain size of 1 μm or less, at least two layers of polycrystalline garnet are laminated, and the crystal lattice constant between adjacent garnet layers is ± 0.3% or more, preferably It is a feature of the present invention that the difference is ± 0.5% or more. In the process of crystallizing the garnet second layer laminated on the garnet first layer just above the already crystallized substrate, the second layer is formed by utilizing the generation of fine crystal grains from the interface between the first layer and the second layer. Refining the crystal grains of. In addition, in order to adjust the coercive force of 1 kOe or more, the residual atomic weight ratio excluding oxygen is 5 at
% Or less Cu is added. Even in a multilayer film of three or more layers, at least one set of two layers can be used as a multiple recording magneto-optical recording medium by applying the present invention. An amorphous transition metal rare earth alloy, Pt, or a multilayer film of Pd and Co can be stacked on such a microcrystalline garnet two-layer film, and can also be applied as a magneto-optical effect enhancing film.

The crystallization of the multilayer film may be carried out by raising the substrate temperature to crystallize during film formation or by heat treatment after film formation.

[0014]

The inventors of the present invention have found from the results of experiments on the single crystal substrate described in the section of the prior art that the polycrystalline garnet layer / polycrystalline garnet layer, or the amorphous garnet and the amorphous garnet structure having a garnet structure after crystallization. It was predicted that the miniaturization effect could be expected at the interface of the quality layer. Therefore, the lattice constant after crystallization on the glass substrate is ± 0.3% or more, preferably ± 0.
Two garnet layers differing by 5% or more were formed, and preferential generation of fine crystal grains from the interface was realized.

Further, the present inventors have discovered that coercive force of 5 kOe or more can be realized by adding Cu to the garnet film for magneto-optical medium (Japanese Patent Application No. 1-3167).
No. 62), it was confirmed that addition of Cu is also effective for increasing coercive force in the present invention.

Tb as a recording layer is formed on the two-layer film of the present invention.
Forming a multilayer film of FeCo, Pt or Pd and Co,
At the time of reproduction, a reproduction signal of high sensitivity was extracted by utilizing the large Faraday rotation angle of the optically uniform fine crystal garnet layer.

Further, by forming the fine crystal grain polycrystalline garnet film of the present invention on a glass disk having a diameter of 5.25 inches, a magneto-optical disk having extremely small noise due to grain boundaries could be manufactured.

Such a garnet multilayer film is formed on the substrate by a sputtering method, a thermal decomposition method or the like. In the sputtering method, Ar gas or a mixed gas of Ar and oxygen may be used to heat the substrate and apply a bias voltage. Even for films of the same type and composition, the crystallization temperature is generally different between crystallization during film formation and crystallization by heat treatment after film formation. To crystallize during film formation, the substrate temperature must be at least 400 ° C. or higher. In order to crystallize by heat treatment after film formation, it is necessary to perform heat treatment at 450 ° C. or higher.

[0019] Combinations of different garnet crystal lattice constants ± 0.3% or _{more, Bi x R 3-x +} u M y Fe
_{5-y + v} O ₁₂ (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 5, −3 ≦
u ≦ 3, −5 ≦ v ≦ 5, R is one or more kinds of rare earth elements containing yttrium, and M is a trivalent metal substitutable with iron). Most promising for use. When the rare earth site is replaced with Bi having a large ionic radius, the crystal lattice constant increases as X increases. In the element that replaces the Fe site,
The crystal lattice constant using Ga or Al having a small ionic radius becomes smaller as Y increases. The crystallization temperature also differs depending on the type and composition of garnet. Therefore, an example of a combination of garnets having crystal lattice constants differing by ± 0.3% or more includes Gd ₃ Fe ₅ O ₁₂ ((12.47 Å / Dy ₃ Fe ₅ O ₁₂ (12.41 Å); lattice constant difference). 0.5%, GGG (12.38 Å / Tb ₃ Fe ₅ O ₁₂ (12.44 Å; a combination of garnets containing different elements such as a lattice constant difference of 0.5%, Bi _0.5 Dy _2.5 Fe ₅ O ₁₂
(12.4 4 angstrom) / Bi ₂ Dy ₁ Fe ₅
O ₁₂ (12.51 Å); lattice constant difference of 0.
6% or Y ₃ Al ₁ Fe ₄ O ₁₂ (12.31 angstrom) / Y ₃ Al ₄ Fe ₁ O ₁₂ (12.09 angstrom); composed of the same kind of element such as a lattice constant difference of 1.8% There are also combinations of garnets with different compositions. Here, the numbers in parentheses represent crystal lattice constants.

[0020]

EXAMPLES The present invention will be further described below based on examples. First, the conditions for producing these garnet films by the high frequency sputtering method are as follows. Target: Ceramic target with a diameter of 80 mm High frequency power: 200 W Sputtering gas: Argon or mixed gas of argon and oxygen Gas pressure: 10-30 mTorr (oxygen partial pressure 30% or less) Base plate: Glass Substrate temperature: 10 ° C to 550 ° C Film thickness : 100 to 5000 angstrom Heat treatment temperature: 540 ° C. to 750 ° C. (in air) Examples 1 to 7 : All Bi _2.6 Dy _0.4 Ga _1.1 Fe
_3.9 O ₁₂ (lattice constant 12.56 Å, average crystal grain size 12 μm when directly formed on a glass substrate)
(Hereinafter referred to as “a layer”) and Bi _1.8 Dy _1.2 Ga _1.5
Fe _3.5 O ₁₂ (lattice constant 12.48 Å,
The lattice constant difference from the a layer is 0.6%, and the average crystal grain size is 3 μm when directly formed on the glass substrate (hereinafter referred to as “b layer”).
By combining the above, polycrystalline garnet films were prepared under various conditions.

Example 1 Layer b was laminated by the sputtering method and then crystallized at 560.degree. Furthermore, after a layer a was stacked on it by a sputtering method, it was crystallized at 640 ° C. At this time, the crystal grain size of the layer b was 0.3 μm.

Example 2 An a layer was laminated at a substrate temperature of 500 ° C. on a b layer prepared at a substrate temperature of 500 ° C. At this time, the crystal grain size of the layer b was 0.1 μm.

Example 3 The production conditions were the same as in Example 1 except that a 3 at% Cu was added using a composite target when laminating the a layer by the sputtering method. This film achieved a coercive force of 5 kOe. At this time, the crystal grain size of the layer b was 0.1 μm.

Example 4 Amorphous a-layer and b-layer were alternately laminated in the order of b / a / b without raising the substrate temperature, and a total of three layers were laminated. Then, only the a-layer was crystallized by heat treatment at 560 ° C. Then, a three-layer film was produced by crystallizing the two b layers by heat treatment at 620 ° C. At this time, the crystal grain size of the layer b was 0.2 μm.

Example 5 At a substrate temperature of 500 ° C., a 6-layer film was prepared by alternately laminating 6 layers a and b containing 2 at% of Cu in the order of a / b / a / b / a / b. . At this time, the coercive force of the a layer is 3.5 k.
The Oe and average crystal grain size were 0.1 μm.

Example 6 A film was prepared by crystallizing by heat treatment, laminating layers b and a, and then laminating an amorphous TbFeCo film thereon using an alloy target. At this time, the average crystal grain size of the layer a is 0.
The Kerr rotation angle of TbFeCo by the laser light having a wavelength of 514 nm which is 1 μm and is incident from the substrate side is enhanced ten times.

Example 7 Layer b was laminated on a 5.25-inch glass disk substrate at a substrate temperature of 500 ° C. using a ceramic target having a diameter of 150 mm. Furthermore, the substrate temperature is 500 ° C.
While maintaining the above condition, an a layer having a coercive force of 5 kOe was formed by adding Cu of 3 at% by using a Cu-added ceramics target having a diameter of 150 mm to form a two-layer film. This Cr film that combines both heat absorption and light reflection
A magneto-optical disk formed on the layer film by using a metal target having a diameter of 150 mm was produced. A carrier / noise ratio of 40 dB or more was achieved with this disk using an Ar laser with a wavelength of 514 nm.

Examples 8 to 15 : Table 1 shows the composition, lattice constant difference, and crystal grain size of each layer of Examples 8 to 15.

[0029]

[Table 1] In either case, the garnet first layer and the garnet second phase, or the garnet first layer and the garnet first layer and the first layer laminated on the first layer after crystallization, the grain size in the second layer from the interface of the amorphous layer having the garnet structure. A garnet two-layer film in which fine polycrystals of 1 μm or less were grown was obtained. It is considered that these fine polycrystalline garnet films are extremely promising as a magneto-optical recording medium.

A detailed description will be given below using micrographs. FIG. 1 is a cross-sectional photograph of a layer a of Example 8 being crystallized by a scanning electron microscope. It can be seen that fine crystal grains of 0.5 μm or less (region B) are preferentially generated from the interface (region A) of the crystallized b layer (average crystal grain size 2 μm). Here, the region C is an amorphous region. Figure 2
FIG. 3 shows a transmission optical micrograph of the two-layer film of Example 8, and FIG. 3 shows the b-layer single-layer film of Example 8 directly formed on the glass substrate. In the two-layer film of Example 8, the crystal grain boundaries found in the directly formed film (average crystal grain size 3 μm) on the glass substrate are miniaturized, and therefore are not clearly observed.

Then, for the a-layer single-layer film of Example 9 having the same film thickness formed directly on the two-layer film of Example 9 and the glass substrate, a wavelength of 633n was applied while applying an external magnetic field of 100 Oe.
Bits were written by a He-Ne laser of m and the shape thereof was examined. The directly formed film on the glass substrate shows a disordered bit shape along the crystal grain boundaries, but the film of Example 9 can write a circular bit having an extremely good shape, and is promising as a magneto-optical recording medium. I understood it.

Examples 16 to 19 : In Examples 1 to 15,
_{Bi x R 3-x + u} M y Fe 5-y + v O 12 ( where, 0 ≦ x ≦
3, 0 ≦ y ≦ 5, −3 ≦ u ≦ 3, −5 ≦ v ≦ 5, R is one or more kinds of rare earth elements including yttrium, and M is a trivalent metal substituting for iron) In the polycrystalline garnet represented by, the first layer and the second layer were u = 0 and v = 0. In Examples 16 to 19, as summarized in Table 2, the case where the composition of the first layer and the second layer represented as described above was u ≠ 0 or v ≠ 0 was evaluated.

[0033]

[Table 2] In either case, the grain size in the second layer is increased from the interface of the amorphous layer having a garnet structure after crystallization by laminating the garnet first layer and the garnet second layer or the garnet first layer and the first layer on each other. A garnet two-layer film in which fine polycrystals of 1 μm or less were grown was obtained. Furthermore, a magneto-optical disk was prepared, and an Ar laser with a wavelength of 514 nm was used.
The carrier / noise ratio was measured. As a result, Examples 16 to 1
The carrier-to-noise ratios of 44, 47, 37, and 42 dB for 9 were respectively.

[0034]

[Effect of the Invention] _{Bi x R 3-x + u} M y Fe 5-y + v O 12 ( where, 0 ≦ x ≦ 3,0 ≦ y ≦ 5, -3 ≦ u ≦ 3, -5 ≦
v ≦ 5, R is one or more kinds of rare earth elements including yttrium, and M is a trivalent metal capable of substituting for iron). In a polycrystalline garnet represented by the following composition, between adjacent garnet layers after crystallization, Laminated garnet layers having different lattice constants of ± 0.3% or more, with respect to the average crystal grain size of the first layer directly on the glass substrate, the average grain size of the polycrystalline garnet of the second layer formed on the first layer By generating fine crystal grains having a small diameter and 1 μm or less, it becomes possible to form a high performance magneto-optical recording medium or a magneto-optical effect enhancing layer on an inexpensive substrate.

[Brief description of drawings]

FIG. 1 Bi _0.3 Tb _2.7 Ga by scanning electron microscope
Bi ₂ Dy ₁ Ga ₁ F formed on _0.3 Fe _4.7 O ₁₂ layer
15000 times the cross-sectional photograph of the microstructure of e ₄ O ₁₂ layer.

FIG. 2 Bi _0.3 Tb _2.7 Ga _0.3 Fe on a glass substrate
_4.7 Bi ₂ Dy ₁ Ga ₁ Fe ₄ O ₁₂ formed on O ₁₂ layer
3 is a transmission optical micrograph at 1000 × of a layer.

FIG. 3 Bi _{2 of} the same thickness formed directly on a glass substrate
It is a 1000 times transmission optical microscope photograph of the fine structure of the Dy ₁ Ga ₁ Fe ₄ O ₁₂ layer.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 31, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 Scanning electron microscope Bi _0.3 Tb _2.7.
Bi ₂ Dy formed on Ga _0.3 Fe _4.7 O ₁₂ layer
₁ is a photograph of a metal structure of 15000 times the microstructure of a ₁ Ga ₁ Fe ₄ O ₁₂ layer.

FIG. 2 Bi _0.3 Tb _2.7 Ga on a glass substrate
Bi ₂ Dy ₁ G formed on _0.3 Fe _4.7 O ₁₂ layer
3 is a photograph of a metallographic structure of the a ₁ Fe ₄ O ₁₂ layer observed by a transmission optical microscope at 1000 times.

FIG. 3 Bi _{2 of} the same thickness formed directly on a glass substrate
2 is a photograph of a metallographic structure of a microstructure of a Dy ₁ Ga ₁ Fe ₄ O ₁₂ layer observed by a transmission optical microscope at 1000 times.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G11B 11/10 K 9075-5D

Claims (6)

[Claims] 1. A Bi _x R _{3-x + u} M formed on a glass substrate.
_y Fe _{5-y + v} O ₁₂ (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 5,
-3 ≦ u ≦ 3, −5 ≦ v ≦ 5, R is one or more rare earth elements including yttrium, and M is a trivalent metal that can replace iron) The average crystal grain size of the first layer directly above the glass substrate is the average of the garnet polycrystal second layer formed on the first layer. A garnet polycrystalline two-layer film for a magneto-optical recording medium having a small grain size and 1 μm or less. 2. The garnet polycrystal second layer formed on the first layer directly above the glass substrate, out of the two garnet layers in claim 1, is 5 at% or less in terms of the atomic weight ratio of the remaining garnet excluding oxygen. Cu is added, and the coercive force of the layer is 1 kOe or more. A garnet polycrystalline two-layer film for a magneto-optical recording medium. 3. A garnet polycrystalline film for a magneto-optical recording medium, comprising three or more layers of garnet laminated, wherein at least two layers are the two-layer film according to claim 1 for a multi-recording magneto-optical medium. Garnet polycrystalline multilayer film. 4. A garnet polycrystalline film for a magneto-optical recording medium, comprising three or more layers of garnet laminated, wherein at least two layers are the two-layer film according to claim 2, for a multi-recording magneto-optical medium. Garnet polycrystalline multilayer film. 5. The garnet bilayer film according to claim 1, further comprising an amorphous rare earth transition metal alloy, or Pt or Pd.
A magneto-optical recording medium or a magneto-optical recording disk, characterized in that a multilayer film of Co and Co is laminated. 6. A magneto-optical recording disk comprising the garnet polycrystalline film according to any one of claims 1, 2, 3, and 4.