JPH05101935A - Garnet polycrystalline film for optical magnetic recording medium, optical magnetic recording medium, and optical magnetic recording disk - Google Patents

Abstract

PURPOSE:To realize a polycrystalline garnet film comprising fine crystal grains on a glass substrate and provide a high performance polycrystalline optical magnetic recording medium using the polycrystalline garnet film. CONSTITUTION:There is laminated bismuth-substituted garnet where a crystal lattice constant of the former is different from the latter by 0.3% or more, and there is separated fine particle garnet polycrystal which is 1mum or less and which has a smaller crystal particle diameter of a first layer from its interface. Such a garnet film has reduced medium noise, and is very useful for an optical magnetic recording medium or a Kerr rotation angle reinforcing layer.

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 noises from grain boundaries of a garnet polycrystalline magneto-optical recording medium and its application.

[0002]

2. Description of the Related Art Garnet type oxide is a magneto-optical recording medium,
It is a material that exhibits excellent performance as a recording material or magneto-optical device such as an optical isolator and a current / magnetic field sensor. In general, this material is non-magnetic in the amorphous state and is therefore used in the single crystal or polycrystal state. However, polycrystalline garnet, which can be manufactured at low cost, is inferior in optical, magnetic or magneto-optical properties to single crystal garnet because of the existence of grain boundaries and the like. 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 realizing high density and high reliability. Garnet material, which has high corrosion resistance and high magneto-optical effect at short wavelength, is the most promising 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. Is being watched. As a method for further improving the recording density, multiple recording using a multilayer film utilizing the translucency of garnet has also been proposed (Ito et al .: Proc. 10th Annual Meeting of the Applied Magnetics Society of Japan, 31 (1986)).

When the garnet film is combined with a conventional amorphous transition metal rare earth alloy or another metal-based magneto-optical recording medium such as 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. A Bi-substituted garnet film formed on a GGG (gallium gadolinium garnet) single crystal substrate exhibits high performance of 60 dB in terms of carrier / noise ratio (signal / noise ratio under standard conditions) in recording / reproducing characteristics (H.
Kano et al: IEEE Trans. Ma
gn. MAG-25 (5), 3737 (198)
9)). However, in the case of a garnet film formed on an inexpensive glass substrate, etc., it is polycrystalline and has a large medium noise due to optical nonuniformity (nonuniform distribution of refractive index) originating 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 due to grain boundaries (eg, M. Abe).
and M.D. Gomi; J. Magn. Magn. M
ater. , 84, 222 (1990)). Additive elements (for example, Ito et al .; Proc. 12th Annual Meeting of the Applied Magnetics Society of Japan, 127 (1989))
Alternatively, a rapid (heat treatment) crystallization method (T. Suzuki
et al; Proceedings of the 13th Applied Magnetics Society Academic Conference,
49 (1988)).

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 single crystal (111) plane, but the lattice constant differs by about 0.3%.
It has been reported that fine crystal grains are not observed on CGMZ (calcium, magnesium, zirconium-substituted gadolinium gallium garnet) single crystal substrates, and that epitaxial growth occurs (Shono; “Light and magnetism-its basics and applications- , 1988 Applied Magnetics Seminar text, 1
07 (1988)).

The inventors of the present invention prepared Bi, Ga-substituted DyFe garnet amorphous films having a garnet structure after crystallization on GGG single crystal substrates of various plane orientations, and detailed the crystallization process by heat treatment. Observed, the crystal lattice constant was ± 0.
It was confirmed that the oriented fine crystal grains of garnet 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 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 smaller than that at the inside of the amorphous film or the surface not in contact with the garnet single crystal. , 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. To aim.

[0009]

The present invention is directed to a garnet polycrystalline film formed of fine crystal grains formed on a substrate and a high performance magneto-optical recording medium to which the garnet polycrystalline film 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.

In the present invention, Bi _x R _3-X N _Y Fe _3-YO
12 Polycrystalline garnet represented by the composition (where 0 ≦ X ≦ 3, 0 ≦ Y ≦ 5, R is one or more kinds of rare earth elements including yttrium, and N is Ga, Al or In). And Garnet grain size of one layer is another
In order to realize a polycrystalline garnet having a crystal grain size smaller than the garnet grain size of one layer and 1 μm or less, the crystal lattice constant between adjacent garnet layers is ± 0.3.
It is characterized by a difference of not less than%, preferably ± 0.5%. In the crystallization process, the generation of fine crystal grains from the interface between the garnet layer and the garnet layer or the amorphous layer having a garnet structure after crystallization is used to refine the crystal grains. Further, in order to adjust the coercive force of 1 kOe or more, the residual atomic weight ratio excluding oxygen is 5 at% or less of 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 or a Pt or Pd / Co multilayer film can be laminated on such a fine crystal garnet two-layer film, and can also be applied as a magneto-optical effect enhancing film.

In crystallization of a multilayer film, 1) stacking is performed while crystallizing by raising the substrate temperature during film formation, 2) stacking one layer at a time by heat treatment after film formation, or 3) crystal of adjacent layers. Amorphous layers are laminated so that the crystallization temperatures are different, and after the layers are laminated, they are heat-treated and crystallized at two or more temperatures, or 4) garnet layers with different crystallization temperatures of adjacent layers are raised while increasing the substrate temperature. While crystallizing more than one layer during film formation 2
Any one of stacking more than one layer and crystallizing the remaining layer by heat treatment after film formation may be used.

[0012]

The inventors of the present invention have found from the results of experiments on a single crystal substrate described in the prior art that even at the interface between a garnet polycrystal layer / garnet polycrystal layer or an amorphous layer having a garnet structure after crystallization. It was predicted that the miniaturization effect could be expected.
Therefore, the lattice constant after crystallization on the glass substrate is ± 0.3.
%, Preferably ± 0.5% or more, two different garnet layers were formed, and preferential generation of fine crystal grains from the interface was realized.

Furthermore, the present inventors have discovered that a coercive force of 5 kOe or more can be realized by adding Cu to the garnet film for magneto-optical media (Japanese Patent Laid-Open No. 31676/1993).
No. 2), it was confirmed that addition of Cu is also effective for increasing coercive force in the present invention. A multi-layered film of TbFeCo or Pt or Pd and Co is formed as a recording layer on the two-layer film of the present invention, and a large Faraday rotation angle of an optically uniform fine crystal garnet layer is utilized during reproduction to achieve high sensitivity. The playback signal was taken out.

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

Gar having different crystal lattice constants of ± 0.3% or more
As a combination of nets, Bi_xR _3-XN_YFe_3-YO
₁₂(Where 0 ≦ X ≦ 3, 0 ≦ Y ≦ 5, R is yttria
One or more kinds of rare earth elements including aluminum, N is Ga or Al
(Representing In), a polycrystalline garnet represented by the composition
However, it is the most promising for magneto-optical recording media. AEON half
If the rare earth site is replaced with Bi, etc., which has a large diameter, it will be crystalline
The child constant increases as X increases. Replace Fe site
For the element to be used, Ga or Al with a small ionic radius is used.
The crystal lattice constant decreases as Y increases. Well
Also, the crystallization temperature varies depending on the type and composition of garnet.
It Therefore, the crystal lattice constants differing by ± 0.3% or more
An example of a net combination is Gd₃Fe_FiveO₁₂(12.4
7A) / Dy₃Fe_FiveO₁₂(12.41A); lattice constant
0.5% difference, GGG (12.38A) / Tb₃Fe_FiveO
₁₂(12.44A); Different types with a lattice constant difference of 0.5%
In addition to the combination of garnet containing the elements of_0.5Dy
_2.5Fe_FiveO₁₂(12.44A) / Bi₂Dy₁Fe_Five
O₁₂(12.51A); lattice constant difference of 0.6% or Y₃Al
₁Fe_FourO₁₂(12.31A) / Y₃Al_FourFe₁O₁₂
(12.09A); Lattice constant difference of 1.8%
A combination of garnets that consist of elements but have different compositions
is there. Here, the number in parentheses represents the crystal lattice constant.

Each of the layers in the garnet multilayer film can also be used as a polycrystalline underlayer simply for forming a metastable layer which requires a garnet structure as an underlayer.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 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) Substrate: Glass Substrate temperature: 10-550 ° C Film thickness: 100 ˜5000 A Heat treatment temperature: 540 ° C. to 750 ° C. (in air) Composition determination method: Assuming that the atomic weight ratio of the metal element and oxygen is 8 to 12, only the metal element is evaluated and calculated by optical emission analysis.

Example 1 Bi_2.6Dy_0.4Ga_1.1Fe_3.9O₁₂(Lattice constant 1
2.56A, average crystal when directly formed on a glass substrate
Particle size 12 μm, hereinafter abbreviated as a layer) and Bi_2.0Dy _1.0G
a_1.5Fe_3.5O₁₂(Lattice constant 12.50A, with a layer
Lattice constant difference 0.5%, flatness when directly formed on glass substrate
A uniform crystal grain size of 3 μm, hereinafter abbreviated as layer b)
Example of making a garnet polycrystalline film according to the claim by the Tatta method
I will give you.

When the film is crystallized by heat treatment after the film formation, the crystallization temperature of the a layer is 560 ° C. and that of the b layer is 620 ° C.
To crystallize during film formation, it is necessary to raise the substrate temperature to 500 ° C. or higher. The b and a layers were laminated at a substrate temperature of 500 ° C. to produce a two-layer film according to claim 1. A at this time
The average crystal grain size of the layer was 0.1 μm.

3 at% Cu was added using a composite target when laminating the a layer under the same sputtering conditions, and 5 k was added.
A coercive force of Oe was achieved, and the two-layer film according to claim 2 was produced. At this time, the average crystal grain size of the layer a was 0.1 μm. After a total of 3 layers of amorphous a and b layers are alternately laminated in the order of b / a / b without increasing the substrate temperature, first, only the a layer is crystallized by heat treatment at 560 ° C., and then heat treatment at 620 ° C. In 2
The three b layers were crystallized to produce a three-layer film according to claim 3. At this time, the average crystal grain size of the layer b was 0.2 μm.

6. A six-layer film according to claim 4, wherein six layers a and b containing 2 at% of Cu added at a substrate temperature of 500 ° C. are alternately laminated in the order of a / b / a / b / a / b. Was produced. At this time, the coercive force of the layer a was 3.5 kOe, and the average crystal grain size was 0.1.
It was 1 μm. Crystallization is performed by heat treatment to stack layers b and a, and an amorphous Tb layer is formed on the layers by using an alloy target.
An FeCo film was laminated to form a film according to claim 5. At this time, the average crystal grain size of the a layer was 0.1 μm, and TbF generated by the laser beam having a wavelength of 514 nm incident from the substrate side was used.
The Kerr rotation angle of eCo was enhanced 10 times.

Layer b was laminated at a substrate temperature of 500 ° C., and 3 at% Cu was added to the layer b using a Cu-added ceramic target having a diameter of 150 mm to form layer a having a coercive force of 5 kOe. A two-layer film was prepared on a 5.25 inch glass disk substrate. Cr that combines heat absorption and light reflection
A film was formed on the two-layer film by using a metal target having a diameter of 150 mm to manufacture a magneto-optical disk according to claim 6. With this disc, an Ar laser with a wavelength of 514 nm was used to achieve a carrier-noise ratio of 50 dB or more.

In each case, a uniform film could be produced in which the crystal grain size of one polycrystalline garnet layer was smaller than that of the other layer and was 1 μm or less. Table 1 summarizes other examples.

[0024]

[Table 1]

In any of Examples 1) to 9), from the interface between the garnet layer and the garnet layer or the amorphous layer having a garnet structure after crystallization, the grain size is smaller and smaller than the crystal grain size in the crystallization process. A garnet two-layer film in which fine polycrystals having a diameter of 1 μm or less were grown was obtained. The fact that these fine polycrystalline garnet films are considered to be extremely promising as a magneto-optical recording medium will be specifically described below with reference to the photographic drawings.

FIG. 1 shows a second embodiment using a scanning electron microscope.
2 is a photograph of a cross section of the a layer during crystallization. 0.5 μ from the interface (region A) of the crystallized b layer (average crystal grain size 2 μm)
It can be seen that fine crystal grains (area B) of m or less are preferentially generated. Here, the region C is an amorphous region. FIG. 2 shows transmission optical micrographs of a) the two-layer film of Example 2 and b) the b-layer single-layer film of Example 2 directly formed on the glass substrate. In the two-layer film of Example 2, the crystal grain boundaries found in the directly formed film (average crystal grain size 3 μm) on the glass substrate are not clearly observed due to the miniaturization.

With respect to the two-layer film of Example 3 and the a-layer single-layer film of Example 3 having the same film thickness formed directly on 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 two-layer film of Example 3 can write a circular bit having an extremely good shape, and is promising as a magneto-optical recording medium. I found out.

[0028]

As described above in the embodiments, B
i _x R _3-X N _Y Fe _3-Y O ₁₂ (where 0 ≦ X ≦ 3, 0
≦ Y ≦ 5, R is one or more kinds of rare earth elements including yttrium, and N is Ga, Al or In), and the lattice constant between adjacent crystallization garnet layers is Whether garnet layers that differ by ± 0.3% or more are laminated to form an interface between the garnet layer and the garnet layer or an amorphous layer having a garnet structure after crystallization and the substrate temperature is raised during film formation to crystallize Alternatively, by crystallizing by heat treatment after film formation, in the crystallization process from the interface, fine crystal grains smaller than the crystal grain size of one layer and having an average crystal grain size of 1 μm or less were successfully generated. The fine crystal grain size garnet polycrystalline film formed on an inexpensive substrate according to the present invention is promising as a magneto-optical recording medium or a magneto-optical effect enhancing layer.

[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
It is a 15,000 times cross-sectional photograph showing the fine crystal structure of the e ₄ O ₁₂ layer.

FIG. 2 a) Bi _0.3 Tb _2.7 Ga _0.3 on a glass substrate
Bi ₂ Dy ₁ Ga ₁ Fe ₄ formed on the Fe _4.7 O ₁₂ layer
3 is a transmission optical microscope photograph at 1000 times showing a fine crystal structure of an O ₁₂ layer and b) a Bi ₂ Dy ₁ Ga ₁ Fe ₄ O ₁₂ film having the same thickness formed directly on a glass substrate.

[Procedure amendment]

[Submission date] January 14, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

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 due to grain boundaries (eg, M. Abe).
and M.D. Gomi; J. Magn. Magn. M
ater. , 84, 222 (1990)). Additive elements (for example, Ito et al .; Proc. 12th Annual Meeting of the Applied Magnetics Society of Japan, 127 ( 1988 ))
Alternatively, a rapid (heat treatment) crystallization method (T. Suzuki
et al; Proceedings of the 13th Applied Magnetics Society Academic Conference,
49 ( 1989 )).

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010] In the present _{invention, Bi x R 3-X M} Y Fe 5-Y O
₁₂ Polycrystalline garnet represented by the composition (where 0 ≦ X ≦ 3, 0 ≦ Y ≦ 5, R is one or more kinds of rare earth elements including yttrium, and M is Ga, Al or In). And Garnet grain size of one layer is another
In order to realize a polycrystalline garnet having a crystal grain size smaller than the garnet grain size of one layer and 1 μm or less, the crystal lattice constant between adjacent garnet layers is ± 0.3.
It is characterized by a difference of not less than%, preferably ± 0.5%. In the crystallization process, the generation of fine crystal grains from the interface between the garnet layer and the garnet layer or the amorphous layer having a garnet structure after crystallization is used to refine the crystal grains. Further, in order to adjust the coercive force of 1 kOe or more, the residual atomic weight ratio excluding oxygen is 5 at% or less of 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 or a Pt or Pd / Co multilayer film can be laminated on such a fine crystal garnet two-layer film, and can also be applied as a magneto-optical effect enhancing film.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

Gar having different crystal lattice constants of ± 0.3% or more
As a combination of nets, Bi_xR _3-X M _YFe _5-Y O
₁₂(Where 0 ≦ X ≦ 3, 0 ≦ Y ≦ 5, R is yttria
One or more rare earth elements, includingMIs Ga, Al
(Representing In), a polycrystalline garnet represented by the composition
However, it is the most promising for magneto-optical recording media. AEON half
If the rare earth site is replaced with Bi, etc., which has a large diameter, it will be crystalline
The child constant increases as X increases. Replace Fe site
For the element to be used, Ga or Al with a small ionic radius is used.
The crystal lattice constant decreases as Y increases. Well
Also, the crystallization temperature varies depending on the type and composition of garnet.
It Therefore, the crystal lattice constants differing by ± 0.3% or more
An example of a net combination is Gd₃Fe_FiveO₁₂(12.4
7A) / Dy₃Fe_FiveO₁₂(12.41A); lattice constant
0.5% difference, GGG (12.38A) / Tb₃Fe_FiveO
₁₂(12.44A); Different types with a lattice constant difference of 0.5%
In addition to the combination of garnet containing the elements of_0.5Dy
_2.5Fe_FiveO₁₂(12.44A) / Bi₂Dy₁Fe_Five
O₁₂(12.51A); lattice constant difference of 0.6% or Y₃Al
₁Fe_FourO₁₂(12.31A) / Y₃Al_FourFe₁O₁₂
(12.09A); Lattice constant difference of 1.8%
A combination of garnets that consist of elements but have different compositions
is there. Here, the number in parentheses represents the crystal lattice constant.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028]

As described above in the embodiments, B
i _x R _3-X M _Y Fe _5-Y O ₁₂ (where 0 ≦ X ≦ 3, 0
≦ Y ≦ 5, R is one or more kinds of rare earth elements including yttrium, and M is Ga, Al, or In, and the polycrystalline garnet represented by the composition has a lattice constant between adjacent garnet layers after crystallization. Whether garnet layers that differ by ± 0.3% or more are laminated to form an interface between the garnet layer and the garnet layer or an amorphous layer having a garnet structure after crystallization and the substrate temperature is raised during film formation to crystallize Alternatively, by crystallizing by heat treatment after film formation, in the crystallization process from the interface, fine crystal grains smaller than the crystal grain size of one layer and having an average crystal grain size of 1 μm or less were successfully generated. The fine crystal grain size garnet polycrystalline film formed on an inexpensive substrate according to the present invention is promising as a magneto-optical recording medium or a magneto-optical effect enhancing layer.

Claims (6)

[Claims] 1. A _{Bi x R 3-X N Y} Fe 3-Y O 12 ( where, 0 ≦ X ≦ 3,0 ≦ Y ≦ 5, R is one or more rare earth elements including yttrium, N is the Ga , Al or In
, Which is composed of two layers having different crystal lattice constants of ± 0.3% or more, and the average crystal grain size of one layer is smaller than that of the other layer. And a garnet polycrystalline film for a magneto-optical recording medium, which is 1 μm or less. 2. The garnet according to claim 1, wherein at least one of the two layers of garnet is added with Cu of 5 at% or less in terms of a residual atomic weight ratio excluding oxygen of the garnet, and the coercive force of the layer is 1 kOe or more. A garnet polycrystalline film for a magneto-optical recording medium, characterized in that 3. A garnet polycrystal for a magneto-optical recording medium, wherein at least two layers in the garnet polycrystal film for a magneto-optical recording medium, in which three or more layers of garnet are laminated, are two-layer films according to claim 1. film. 4. A garnet polycrystal for a magneto-optical recording medium, wherein at least two layers in the garnet polycrystal film for a magneto-optical recording medium in which three or more layers of garnet are laminated are at least two layers. film. 5. The amorphous rare earth-transition metal alloy, Pt or P is added to the garnet two-layer film according to claim 1.
A magneto-optical recording medium or a magneto-optical recording disk, wherein a multilayer film of d 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.