JPH1092640A - Ultra high-density magnetic recording medium and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely cut off the magnetic interaction between ferromagnetic crystal grains and, at the same time, to improve the coercive force of a magnetic recording medium by forming a magnetic recording layer having a ferrite granular structure containing fine ferromagnetic ferrite particles in a nonmagnetic base material on a nonmagnetic substrate. SOLUTION: After an SiO2 film 2 is formed on an Si substrate 1 and a granular film composed of an SiO2 base material. containing FeCo metallic particles is formed by sputtering on the heat-resistant nonmagnetic substrate 1, the granular film 3 is changed to a ferromagnetic ferrite/SiO2 granular film 3 by heat-treating the granular film in a vacuum. Then a carbon film is formed on the surface of the granular film 3 as a protective film 4. Most of the crystals grown in the film 3 after heat treatment are composed of Fe4 O4 ferrite crystals, CoFe2 O4 ferrite crystals, a small quantity of γ-Fe2 O3 ferrite crystals, etc. In addition, the FeCo/SiO2 volumetric ratio in the film 3 is adjusted to 30:70 to 70:30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium, a method for manufacturing the same, and a magnetic disk drive.

[0002]

2. Description of the Related Art A magnetic recording device is used as an external storage device of an information processing device. With an increase in the amount of information handled by information processing apparatuses, it has become essential to improve the recording density of magnetic recording apparatuses. However, when the recording density of the magnetic recording medium used in the conventional magnetic recording device is increased,
Since there is a problem that the reproduction output decreases and the noise increases, there is a demand for a magnetic recording medium capable of high-density recording, high reproduction output and low noise.

[0003] Noise generated from a medium is mainly caused by variation in magnetization in a magnetization transition portion, and variation in magnetization is caused by magnetic interaction between ferromagnetic crystal grains constituting a recording layer. Therefore, in order to reduce the medium noise, it is effective to weaken the magnetic interaction between the ferromagnetic crystal grains. A conventional magnetic recording medium is a ternary or quaternary based on Co made by sputtering.
Generally, a thin film of the original alloy was used, and noise was reduced by segregating non-magnetic addition elements between ferromagnetic crystal grains depending on the composition and preparation conditions to weaken magnetic interaction. . However, since Co-based and Fe-based alloys are basically solid-solution alloys, ferromagnetic crystal particles cannot be completely isolated even if segregation is promoted depending on the composition and preparation conditions. Therefore, the magnetic interaction between the ferromagnetic crystal grains could not be completely cut off.

Further, in the ferromagnetic metal crystal grain granular medium, the magnetic recording layer is formed of a ferromagnetic metal crystal particle and a non-magnetic base material which are insoluble in each other, so that the magnetic mutual layer between the ferromagnetic crystal particles is magnetic. Although the function can be completely cut off, there is a disadvantage that the coercive force is small.

[0005]

For the above reasons, a magnetic recording medium having a large coercive force while completely isolating the ferromagnetic crystal grains to completely cut off the magnetic interaction between the ferromagnetic crystal grains is required. It has been. The present invention aims to answer this need.

[0006]

In order to solve the above-mentioned problems, the present invention provides a magnetic recording layer having a ferrite granular structure containing ferromagnetic ferrite fine particles in a non-magnetic base material. Compared to the conventional metallic granular structure, the ferrite granular structure improves the coercive force, and the granular structure in the non-magnetic base material cuts off the magnetic interaction between ferromagnetic particles to reduce noise. Is done.

Ferrite has the general formula MO.Fe ₂ O ₃ (M
Is a divalent metal), and particularly those exhibiting ferromagnetism are Fe ₃ O ₄ , CoFe ₂ O ₄ , and NiF.
_{e 2 O 4, MnFe 2 O} 4, including barium _{ferrite, CoFe 2 O 4, Fe 3} O 4 is preferred. Ferrite particles include by-products or other ferromagnetic materials,
For example, γ-Fe ₂ O ₃ may be included.

The non-magnetic base material may be any non-magnetic material which is insoluble in ferrite, such as SiO ₂ , Al ₂ O ₃ , MgO, Z
rO _{2 and the} like are exemplified. The ferrite granular structure is used to suppress the magnetic interaction between the ferromagnetic ferrite fine particles. Therefore, it is preferable that the ferromagnetic ferrite fine particles exist independently in the nonmagnetic base material. On the other hand, in order to increase the coercive force, the ferromagnetic ferrite should be more. Therefore, the volume ratio between the ferromagnetic ferrite and the nonmagnetic base material is preferably in the range of 30:70 to 70:30, and more preferably in the range of 40:60 to 60:40.

The thickness of the magnetic recording layer having the ferrite granular structure is related to the size of the ferromagnetic ferrite fine particles, and is generally 100 nm or less, preferably 10 to 50 nm. The particle size of the ferromagnetic ferrite fine particles in the ferrite granular structure is generally 5 to 50 nm, preferably 10 to 3 nm.
0 nm. If the particle size is small, the coercive force decreases, while if the particle size is large, noise tends to occur.

A magnetic recording layer having a ferrite granular structure is formed on a non-magnetic substrate. The non-magnetic substrate is not particularly limited, but is preferably a non-magnetic heat-resistant substrate (Si, SiO ₂ , C, sapphire, crystallized glass, etc.) that can be heat-treated at a high temperature of 400 ° C. or higher. A magnetic recording layer having a ferrite granular structure is formed on a non-magnetic substrate to obtain a magnetic recording medium. A magnetic disk drive including the magnetic recording medium and the magnetic head can be configured.

In order to form a magnetic recording layer having a ferrite granular structure, a metal element constituting a ferromagnetic ferrite is sputtered simultaneously with a nonmagnetic base material to form a thin film having the above-mentioned metal element and a metal granular structure. A method of converting the metal element into ferromagnetic ferrite by heat treatment can be used. It is preferable to use a composite target for simultaneous sputtering.

The heat treatment is performed at a temperature of 400 ° C. or more, preferably in the range of 500 to 800 ° C. The higher the heat treatment temperature, the greater the coercive force. If the heat treatment temperature is too high, the particles grow and become too large. Further heat treatment under high vacuum,
For example, it is preferable to perform the process at about 1 × 10 ⁻⁶ Torr. Oxidation due to the presence of a small amount of oxygen is appropriate. If the amount of oxygen is too large, the oxidation proceeds to form oxides other than ferrite.

The magnetic recording layer having a ferrite granular structure formed as described above generally has a thickness of 1000 Oe or more.
It can have a coercive force of 000 Oe or more, especially 3000 Oe.

[0014]

FIG. 1 is a sectional view of a magnetic recording medium according to an embodiment of the present invention. This medium includes a Si substrate 1, a magnetic recording layer 3, and a protective coating 4 formed on the magnetic recording layer. A layer of liquid lubricant is usually added on the protective coating. In addition, Si
To prevent diffusion bonding between Si and the magnetic material on the surface of the substrate,
A thermal oxide film (SiO ₂ ) 2 is provided in advance.

FIG. 2 shows a procedure for producing a magnetic recording medium according to an embodiment of the present invention. Fe on the heat-resistant non-magnetic substrate (1, 2)
After forming a granular film 3 'of Co metal particles / SiO ₂ base material by sputtering (FIG. 2A), this is heat-treated under vacuum to be converted into a ferromagnetic ferrite / SiO ₂ granular film 3 ( 2B, carbon is formed as a protective film 4 on the surface (FIG. 2C).

Here, the heat-resistant non-magnetic substrate is a Si substrate, a C substrate or the like which can be heat-treated at a high temperature of 400 ° C. or more. FIG. 3 shows a schematic diagram of the composite target used in the example. S
A square Co plate 12 and a Fe plate 13 are concentrically arranged on an iO ₂ target 11. By changing the number of Co plates and Fe plates, the composition ratio of the ferromagnetic metal crystal grains of the magnetic recording layer and the nonmagnetic base material can be changed without causing a gradient in the radial composition on the film-formed medium. Can be done.

Using this composite target, 5 × 1
Magnetron sputtering is performed under a vacuum of 0 ^-7 Torr, an Ar gas pressure of 5 mTorr, a substrate temperature of room temperature (about 50 ° C.), a sputtering power of 200 W, and an F film having a film thickness of 10 to 300 nm.
An eCo / SiO ₂ granular film 3 ′ was formed. After the sputtering, heat treatment was performed at 500 to 800 ° C. for 1 hour in a high vacuum of 1 × 10 ⁻⁶ Torr, and then carbon was deposited to a thickness of 20 nm.

FIG. 4 shows the results of X-ray diffraction of the granular films 3 'and 3'. No diffraction peak was obtained in the film before the heat treatment as compared with the Si substrate. In the heat-treated film, a diffraction peak indicating crystallinity was obtained. Since the diffraction peak is increased by the heat treatment, it is understood that the crystal grains are grown by the heat treatment. The crystal growing in the film after the heat treatment is an oxide of Fe and Co, and the oxide is mainly Fe ₃ O.
₄ , ferrite such as CoFe ₂ O ₄ and a small amount of γ-Fe ₂ O ₃ .

FIG. 5 shows an FeCo body in which Hc is almost maximum.
FeCo oxide / SiO with a product ratio of 56%_Two(Film thickness 20n
m) shows TEM images before heat treatment and after heat treatment at 700 ° C.
Was. The particle size of the film before heat treatment is about 50 °, and the particles
Well aligned, with SiO between grains _TwoLike cut by
I understand the child better. Particles in the film after heat treatment are 20-50 nm
Growing to a degree. Coercivity increases with grain size growth
It is considered great.

FIG. 6 shows the relationship between the coercive force and the FeCo volume ratio at different heat treatment temperatures. The coercive force does not depend on the FeCo volume ratio before the heat treatment and is several tens of Oe. However, when a heat treatment at 500 ° C. or more is applied, the coercive force shows a large value of 1000 Oe or more. The coercive force increases as the volume ratio of FeCo increases, and becomes about 1000 Oe or more at about 30% to 70%. When the volume ratio exceeds 60%, the coercive force decreases rapidly,
If it is 70% or more, it shows soft magnetism. The higher the heat treatment temperature, the greater the coercive force.

FIG. 7 shows the relationship between the coercive force and the FeCo volume ratio for each film thickness. The coercive force greatly depends on the film thickness. The coercive force is most likely to be obtained when the film thickness is around 20 nm, and when the film thickness is larger than 100 nm, the coercive force becomes 1000 Oe or less. FIG. 8 shows a Henkel plot of FeCo oxide / SiO ₂ (51 vol.% Of FeCo medium). FeCo oxide / S
The iO ₂ medium has a curve that is quite close to the theoretical curve of SW particles (Stoner-Wall-Firth particles), and it is considered that the exchange interaction has been sufficiently cut off.

As a result of evaluating the noise of the medium according to the present invention, the medium noise did not increase in the high-density recording area in all the media of the examples. Therefore, it was shown that the present invention can provide a thin film medium suitable for high-density recording. FIG. 9 shows an example of a magnetic disk drive on which the magnetic disk 21 manufactured as described above is mounted. A magnetic head 22 of a magnetoresistive effect type is arranged to face the magnetic disk 21. In the figure, reference numeral 23 denotes a disc holder,
Is a voice coil motor for driving a magnetic head, 25 is a housing, 26 is a semiconductor integrated circuit device, 27 is a connector, and 28 is an arm made of an elastic body that supports the magnetic head 22.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a ferrite granular thin film on a substrate.

FIG. 2 is a diagram showing a process for producing a thin film of the present invention.

FIG. 3 is a schematic diagram showing a composite target for sputtering a thin film of the present invention.

FIG. 4 is an X-ray diffraction pattern of a ferrite granular thin film.

FIG. 5 is a diagram showing a ferrite granular thin film 7 of the present invention.
3 shows TEM images that were heat-treated at 00 ° C. and before heat treatment.

FIG. 6 is a diagram showing the relationship between the coercive force and the FeCo volume ratio of a ferrite granular thin film heat-treated at various temperatures and before heat treatment.

FIG. 7 is a diagram showing a relationship between a coercive force and a FeCo volume ratio of a ferrite granular thin film formed of various thin films.

FIG. 8 is a Henkel plot showing the magnetic interaction of a ferrite granular thin film.

FIG. 9 shows a card-type magnetic disk drive equipped with a magnetic disk.

[Explanation of symbols]

1 ... Si substrate 2 ... SiO ₂ film 3 ... ferromagnetic ferrite / SiO ₂ granular film 3 '... FeCo / SiO ₂ granular film 4 ... carbon protective film 11 ... SiO ₂ 12 ... Fe chips 13 ... Co chips

Claims (6)

[Claims] 1. A magnetic recording medium having a ferrite granular structure magnetic recording layer containing ferromagnetic ferrite fine particles in a nonmagnetic base material on a nonmagnetic substrate. 2. The ferromagnetic ferrite according to claim 1, wherein said ferromagnetic ferrite is CoFe ₂ O _4.
And / or Fe ₃ O ₄ , optionally γ-Fe ₂ O ₃
The magnetic recording medium according to claim 1, further comprising: 3. The magnetic recording medium according to claim 1, wherein said non-magnetic base material is SiO ₂ . 4. The volume ratio of the ferromagnetic ferrite to the non-magnetic base material is from 30:70 to 70:30.
The magnetic recording medium according to any one of the above items. 5. A magnetic disk drive comprising: the magnetic recording medium according to claim 1; and a magnetic head arranged to face the magnetic recording medium. 6. A thin film having a metal granular structure including a ferromagnetic ferrite constituent metal element metal fine particle in a nonmagnetic base material by simultaneous sputtering from a nonmagnetic base material target and a target of a metal element constituting ferromagnetic ferrite. Is formed on a non-magnetic substrate, and the thin film is heat-treated at a temperature of 500 ° C. or more to form a ferrite granular structure magnetic recording layer made of a non-magnetic base material containing crystalline ferromagnetic ferrite fine particles. Of manufacturing a magnetic recording medium.