JP2001176045A - Magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in surface smoothness without reducing its high coercive force. SOLUTION: The magnetic recording medium consisting of a substrate and a maghemite thin film formed thereon is characterized in that the maghemite thin film has 10-50 nm film thickness and 0.1-0.7 nm centerline mean roughness and 1-10 nm maximum roughness Rmax of its surface respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a high coercive force and excellent surface smoothness.

[0002]

2. Description of the Related Art In recent years, in magnetic recording devices such as hard disks, there has been a remarkable tendency to reduce the size and reliability of information devices and systems. A recording medium is required, and the demand is increasing.

A magnetic recording medium satisfying such characteristics is required to have a large coercive force and to reduce a distance (magnetic spacing) between a magnetic recording layer and a magnetic head.

As a magnetic recording medium having a large coercive force, a magnetic recording medium comprising a base and a magnetic thin film formed on the base is widely known.

[0005] Magnetic thin films that have been put to practical use in magnetic recording media are roughly classified into oxide magnetic thin films such as maghemite (published by the Institute of Electronics, Communication and Communication Engineers, “Technical Report of the Institute of Electronics and Communication Engineers”, (1981) MR81-20, 5-12 pages, "Ceramics" (1
986), Vol. 24, No. 1, pp. 21-24, JP-B-51-4086, JP-B-5-63925, etc.) and alloy magnetic thin films such as CoCr alloys.

The former is excellent in oxidation resistance and corrosion resistance because it is an oxide. As a result, it has excellent stability over time and a small change in magnetic properties over time.
In addition, since the oxide is harder than the metal, a protective film is not required because the oxide is harder, and the magnetic spacing (the distance between the magnetic head and the magnetic recording layer) can be reduced as compared with the alloy magnetic thin film medium.
It is optimal as a high-density recording medium.

Attempts have been made to increase the coercive force of the maghemite thin film by containing cobalt, but on the other hand, there is a tendency that the stability over time is deteriorated by the influence of heat or the like as the cobalt content increases. is there.

The present inventors have completed a maghemite thin film having a high coercive force even with a low cobalt content by controlling the spacing between specific surfaces of maghemite (Japanese Unexamined Patent Publication No. 11-110732). Gazette, JP-A-11-110732).

The latter has a high coercive force of about 2000 Oe or more, but the alloy material itself is easily oxidized, and as a result, the stability over time is poor and the magnetic properties are liable to be deteriorated.

In order to prevent the deterioration of magnetic properties due to the oxidation, the surface of the alloy magnetic thin film is usually coated with diamond-like carbon or SiO _{2 having} a thickness of about 100 to 200 ° as a protective film. The magnetic spacing is increased by the thickness of the film.

On the other hand, in the magnetic recording medium, in order to reduce the magnetic spacing, it is necessary to reduce the flying height of the magnetic head as much as possible and to stably fly the magnetic head. In a conventional hard disk drive, a certain degree of surface roughness was required to prevent the magnetic recording medium and the magnetic head from adsorbing by the meniscus force when the magnetic head was stationary. At present, the improvement of the hardware system eliminates the need for surface roughness for preventing adsorption, and it is required that the magnetic thin film used for the magnetic recording medium has better surface smoothness.

It is known that when the surface of the magnetic recording medium is not smooth, it appears as medium noise, and it is necessary to reduce the surface roughness of the magnetic thin film in order to reduce the noise.

At present, a magnetic recording medium using an oxide magnetic thin film has a very thin magnetic thin film of 50 nm or less, so that the surface properties of the magnetic thin film largely depend on the surface properties of the substrate. Therefore, there is a demand for a technique of using a substrate having excellent surface smoothness and further smoothing the surface of the magnetic thin film.

Conventionally, as a method for producing a maghemite thin film, 1) a hematite thin film is formed on a substrate, and the hematite thin film is reduced in a temperature range of 230 to 320 ° C. to transform into a magnetite thin film. 290
2) A method of forming a magnetite thin film on a substrate and oxidizing the magnetite thin film at 320 ° C. or higher is known.

As a technique for improving the surface properties of a magnetic recording medium comprising a magnetic iron oxide thin film, a method of optimizing heat treatment conditions to improve the surface smoothness (Japanese Patent No. 28164)
No. 72), and a method of performing sputter etching on the surface of a magnetic recording layer made of an alloy magnetic thin film using oxygen gas (Japanese Patent Application Laid-Open No. 10-50544).

[0016]

A magnetic recording medium comprising a maghemite thin film having an excellent surface smoothness while maintaining a high coercive force as much as possible has been most demanded at present, but has not been obtained yet. .

That is, according to the method described in the aforementioned Japanese Patent No. 2816472, the surface roughness of the glass substrate is reduced by polishing or the like, and the conditions for oxidizing the magnetite thin film in the atmosphere are selected so that magnetic recording with a low Rmax is achieved. The media is manufactured, but what is disclosed in the examples is
What is a method for improving the surface roughness of a magnetic recording medium while maintaining a high coercive force as much as possible in a very thin thin film having a magnetic thin film thickness of about 200 nm and a magnetic thin film thickness of 50 nm or less? It is hard to say.

The method described in Japanese Patent Application Laid-Open No. H10-50544 is a technique for improving the surface smoothness of a magnetic recording medium comprising an alloy magnetic thin film containing Co as a main component. On the other hand, plasma processing is performed. When the same plasma treatment is performed on the maghemite thin film in the present invention, local discoloration is observed, and the expected effect cannot be obtained.

Also, Japanese Patent Application Laid-Open Nos. 11-110732 and 11-110732 describe that a maghemite thin film having a high coercive force can be obtained by controlling the plane spacing. No mention is made of the surface smoothness, and the obtained maghemite thin film is not sufficiently satisfactory in surface smoothness.

Accordingly, it is a technical object of the present invention to obtain a maghemite thin film capable of improving the surface smoothness of a magnetic layer without lowering a high coercive force, in an industrially and economically advantageous manner.

[0021]

The above technical object can be achieved by the present invention as described below.

That is, the present invention provides a magnetic recording medium comprising a substrate and a maghemite thin film formed on the substrate, wherein the maghemite thin film has a thickness of 10 to 50 nm and a center line of the surface of the maghemite thin film. Average roughness R
a is 0.1 to 0.7 nm and the maximum roughness Rmax is 1 to 10 nm (Invention 1).

The present invention also provides a magnetic recording medium comprising a base and a maghemite thin film formed on the base, wherein a nickel oxide base film is formed between the base and the maghemite thin film, The thickness of the thin film is 10 to 50 nm, and the center line average roughness Ra of the surface of the maghemite thin film is 0.1 to 0.7 nm.
Wherein the maximum roughness Rmax is 1 to 10 nm (Invention 2).

Further, according to the present invention, in a method for manufacturing a magnetic recording medium in which a magnetite thin film is formed on a substrate and the magnetite thin film is oxidized into a maghemite thin film, oxygen gas or oxygen is supplied to the magnetite thin film before oxidation. A method for manufacturing a magnetic recording medium according to the first aspect of the present invention, wherein plasma processing is performed using a mixed gas containing the mixed gas.

Further, the present invention provides a method for forming a magnetite thin film by forming a nickel oxide base film on a substrate, forming a magnetite thin film on the nickel oxide base film, and oxidizing the magnetite thin film to form a maghemite thin film. A method for manufacturing a magnetic recording medium according to the second aspect of the present invention, wherein the magnetite thin film before oxidation is subjected to a plasma treatment with an oxygen gas or a mixed gas containing oxygen in the method for manufacturing a recording medium.

The structure of the present invention will be described in more detail as follows.

First, the magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention comprises a base and a maghemite thin film formed on the base.

The substrate in the present invention may be a commonly used substrate material such as a plastic substrate or a glass substrate, and is preferably a glass substrate. Further, the center line average roughness Ra of the surface of the substrate used in the present invention is usually 0.6 nm or less, preferably 0.1 to 0.5 nm, and the maximum roughness Rmax is usually 8 nm or less, preferably 1 nm or less.
７7 nm.

The thickness of the maghemite thin film in the present invention is 10 to 50 nm. Preferably 10 to 30 n
m, more preferably 10 to 20 nm. Film thickness is 10
159.2 kA / m (2000 O
e) It is difficult to obtain a magnetic recording medium having the above coercive force value. If the thickness exceeds 50 nm, it is difficult to obtain a uniform magnetization state up to the deep portion of the magnetic thin film when recording a signal, and it is difficult to obtain good recording / reproducing characteristics.

Maghemite is represented by the general formula γ-Fe ₂ O ₃ , but may contain a small amount of Fe ²⁺ in the present invention.

As the maghemite thin film, a predetermined amount of cobalt may be added to improve the coercive force. The amount of cobalt is 0.2: 1 or less in molar ratio to Fe, preferably 0.01: 1 to 0.1: 1. When the ratio is less than 0.01: 1, it is difficult to obtain a magnetic recording medium having a higher coercive force of 159.2 kA / m (2000 Oe) or more.
If it exceeds 0.2: 1, a magnetic recording medium having excellent stability over time cannot be obtained.

It should be noted that Mn and N other than cobalt which are usually used for improving various properties of the maghemite thin film are used.
If necessary, i, Cu, Ti, Zn, etc. may be contained in a molar ratio of about 0.005: 1 to 0.04: 1 with respect to Fe. In this case, a magnetic recording medium having a high coercive force is obtained. It becomes easy to be.

The center line average roughness Ra of the surface roughness of the maghemite thin film is usually 0.1 to 0.7 nm, preferably 0.1 to 0.65 nm, and more preferably 0.1 to 0.6 nm.
2 nm. If it exceeds 0.7 nm, the effect of the present invention cannot be obtained.

The maximum roughness Rmax of the surface roughness of the maghemite thin film is usually 1 to 10 nm, preferably 1 to 9.5.
nm. If it exceeds 10 nm, the effect of the present invention cannot be obtained.

The magnetic recording medium according to the present invention has a saturation magnetization (magnetization at an applied magnetic field of 1591.5 kA / m (20 kOe)) of 0.276 to 0.377 T (220 to 377 T).
00 emu / cm ³ ), preferably 0.289-0.3
52T (230 to 280 emu / cm ³ ), more preferably 0.289 to 0.327 T (230 to 260 emu)
/ Cm ³ ), and the coercive force value is usually 143.2 kA.
/ M (1800 Oe) or more, preferably 151.2 kA
/ M (1900 Oe) or more. The upper limit is 31
It is 8.3 kA / m (4000 Oe).

The magnetic recording medium according to the present invention comprising a maghemite thin film containing cobalt has a coercive force value of usually 15
9.2 kA / m (2000 Oe) or more, preferably 17
It is at least 5.1 kA / m (2200 Oe), more preferably at least 238.7 kA / m (3000 Oe). Its upper limit is 318.3 kA / m (4000 Oe).

The magnetic recording medium according to the present invention may use a nickel oxide thin film as a base film of the maghemite thin film. When a nickel oxide thin film is used as a base film, the magnetic properties, particularly the coercive force, are improved, and a higher coercive force can be realized with a thinner maghemite thin film as compared with a case without a base film. Further, by making the maghemite thin film thinner, the surface smoothness targeted by the present invention is further improved. The thickness of the nickel oxide thin film is 50 to 1
00 nm is preferred.

In the case of the magnetic recording medium according to the present invention having a base film, the center line average roughness Ra of the surface roughness of the maghemite thin film is usually 0.1 to 0.7 nm, preferably 0.1 to 0.7 nm.
-0.65 nm, more preferably 0.1-0.6 nm,
Still more preferably, it is 0.1 to 0.56 nm. 0.
If it exceeds 7 nm, the effect of the present invention cannot be obtained.

In the case of the magnetic recording medium according to the present invention having an underlayer, the maximum roughness R of the surface roughness of the maghemite thin film
max is usually 1 to 10 nm, preferably 1 to 9 nm, more preferably 1 to 8 nm, and still more preferably 1 to 7.
5 nm. If it exceeds 10 nm, the effect of the present invention cannot be obtained.

The magnetic recording medium according to the present invention having a base film has a saturation magnetization value (applied magnetic field of 1591.5 kA / m (20
kOe) is 0.276-0.377.
T (220-300 emu / cm ³ ), preferably 0.1T.
289-0.352T (230-280 emu / c
m ³ ), more preferably 0.289 to 0.327 (23
0 to 260 emu / cm ³ ), and the coercive force value is usually 159.2 kA / m (2000 Oe) or more, preferably 175.1 kA / m (2200 Oe) or more, and more preferably 222.8 kA / m (2800 Oe). ) That is all. The upper limit is 636.6 kA / m (8000O
e).

The magnetic recording medium according to the present invention, which has a base film and is made of a maghemite thin film containing cobalt, usually has a coercive force value of 175.1 kA / m (2200O
e) above, preferably 198.9 kA / m (2500 O
e) above, more preferably 254.6 kA / m (320
0 Oe) or more. Its upper limit is 636.6 kA / m
(8000 Oe).

Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.

In the magnetic recording medium according to the present invention, the magnetite thin film is oxidized in a temperature range of 200 to 450 ° C. to form a maghemite thin film. It can be obtained by oxidizing the magnetite thin film after the treatment.

The magnetite thin film may be formed by an ordinary method. For example, a so-called sputtering method is used in which a magnetite is generated and deposited while introducing a mixed gas of oxygen and a rare gas using an alloy of Fe as a target. The magnetite thin film may be formed on the substrate while controlling the flow rate of oxygen (CCM) in the mixed gas and the deposition rate (nm / min) of magnetite.

The oxygen flow rate (CCM) in the mixed gas with respect to the magnetite deposition rate (nm / min) depends on various conditions for obtaining a magnetite thin film by oxidizing the Fe alloy target, for example, the type, structure, and total It differs in various ways depending on gas pressure, substrate temperature, sputtering target area, and the like.

The magnetite thin film before the plasma treatment has a thickness of 10 to 50 nm and has a center line average roughness R of the surface roughness.
a is 0.1 to 0.7 nm, and the maximum roughness Rmax is 1 to 10
nm is preferred.

In the plasma treatment according to the present invention, the magnetite thin film is subjected to a plasma treatment at a substrate temperature of 100 to 220 ° C., preferably 150 to 220 ° C. If the substrate temperature is out of the above range, a sufficient effect cannot be obtained.

The atmosphere for the plasma treatment is an oxygen gas or a mixed gas atmosphere containing an oxygen gas. As the mixed gas containing oxygen gas, a mixed gas of oxygen gas and a rare gas is preferable, and as the rare gas, helium, neon, argon,
Any of krypton, xenon, and radon can be used. Considering economy, argon is preferred. In the case of a mixed gas, the mixing ratio of oxygen gas and rare gas is 10
0: 0 to 50:50.

The processing time of the plasma processing in the present invention is 30 seconds to 30 minutes, more preferably 1.5 to 3 minutes.
0 minutes. If the processing time is outside the above range, a sufficient effect cannot be obtained.

The magnetite thin film after the plasma treatment has a thickness of 10 to 50 nm and has a center line average roughness R of the surface roughness.
a is 0.1 to 0.7 nm, and the maximum roughness Rmax is 1 to 10
nm is preferred.

When a nickel oxide thin film is used as a base film, a nickel oxide thin film may be formed on a substrate in advance, and then a magnetite thin film may be formed in the same manner as described above.

[0053]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.
It is as follows.

Surface roughness of magnetite thin film and maghemite thin film (center line average roughness Ra, maximum roughness Rmax)
Is an atomic force microscope (Digital Instruments D
I. Was evaluated in a 5 μm square area.

The thickness of the magnetic layer of the magnetite thin film and the maghemite thin film is determined by writing a line on the substrate with a Magic (registered trademark) pen before forming the film, removing the line with an organic solvent after forming the film, and The deposited film is simultaneously removed. The step formed in this way is measured with a stylus type surface roughness meter (DEKT).
AK) and the thickness of the thin film was calculated.

The oxidation of the magnetite thin film to the maghemite thin film was confirmed by a change in the surface electric resistance of the thin film, which is one of the criteria. That is, while the surface electric resistance of the magnetite thin film is 0.001 to 0.5 MΩ, the surface electric resistance of the maghemite thin film increases and changes to 1 to 100 MΩ. Measurement of surface electrical resistance is available from Insulat
The measurement was carried out using an ion Tester DM-1527 (manufactured by Sanwa Denki Keiki Co., Ltd.) with the distance between the two probes being 10 mm.

The magnetic properties such as the coercive force and the saturation magnetization of the magnetic recording medium were shown by values measured using a “vibrating sample magnetometer VSM” (manufactured by Toei Kogyo Co., Ltd.). The maximum applied magnetic field was measured at 1591.5 kA / m (20 kOe).

The X-ray diffraction pattern of each thin film was shown by a value measured by "X-ray diffractometer RAD-IIA" (manufactured by Rigaku Corporation). The measurement conditions were: tube used: Fe, tube voltage:
40 kV, tube current: 25 mA, goniometer, sampling width: 0.010 °, scanning speed: 1.000 ° /
min, divergence slit: 1 °, scattering slit: 1 °, light receiving slit: 0.30 mm, and diffraction angle (2θ) of 30.
The area from 00 ° to 60.00 ° was measured.

A manufacturing method when a maghemite thin film is formed directly on a substrate will be described. Center line average roughness Ra is 0.20n
m, an iron containing cobalt on a crystallized glass substrate having a maximum roughness Rmax of 5.00 nm by reactive sputtering using an RF sputtering apparatus (high-frequency high-rate sputtering apparatus SH-250H-T06, manufactured by Nihon Vacuum). (Fe containing 4 wt% Co)
By sputtering the target, a maghemite thin film containing cobalt (Co: Fe molar ratio of 0.04:
1) was formed (substrate temperature 220 ° C., gas pressure 9 mTorr)
r). The obtained magnetite thin film has a thickness of 48 nm,
Center line average roughness Ra is 0.57 nm, maximum roughness Rmax
Was 8.00 nm.

Next, oxygen gas was introduced into the RF sputtering apparatus, plasma was generated in an etching mode, and the magnetite thin film was irradiated for 30 minutes (substrate temperature: 180 ° C., gas pressure: 9 mTorr, oxygen: argon = 100). : 0).

The magnetite thin film after the plasma treatment has an R
a was 0.62 nm and Rmax was 8.12 nm.

Subsequently, it was oxidized in the air at 320 ° C. for 60 minutes to obtain a cobalt-containing maghemite thin film (Co: Fe molar ratio: 0.04: 1).

The obtained cobalt-containing maghemite thin film has a thickness of 48 nm and a center line average roughness R of the surface roughness.
a is 0.64 nm, the maximum roughness Rmax is 8.72 nm,
The coercive force was 245.1 kA / m (3080 Oe), and the saturation magnetization value was 0.306 T (244 emu / cm ³ ).

On the other hand, the cobalt-containing maghemite thin film obtained without performing the plasma treatment has a center line average roughness Ra of 0.88 nm and a maximum roughness Rmax of 1 among the surface roughnesses.
4.7 nm, coercive force 238.8 kA / m (3001O
e), the saturation magnetization value is 0.320 T (255 emu / cm
³ ). Therefore, the surface smoothness can be improved while maintaining a high coercive force as much as possible by the plasma treatment before oxidation.

[0065]

First, the most important point in the present invention is that the plasma treatment of the magnetite thin film before oxidation improves the surface smoothness of the maghemite thin film as a final product.

Although the reason why the surface smoothness of the maghemite thin film is improved is not yet clear, the present inventor has conducted a plasma treatment on the magnetite thin film before oxidization so that a portion of the magnetite thin film where oxidation is insufficient is performed. Oxidation is promoted to form a more homogeneous magnetite thin film,
Then, it is presumed that when the maghemite thin film is converted into a maghemite thin film by oxidation treatment, more uniform oxidation occurs, and as a result, a maghemite thin film having excellent surface smoothness is obtained. In the case where only the oxidation treatment is performed without performing the plasma treatment, the oxidation treatment is performed while including the insufficiently oxidized portion, and the surface property of the obtained maghemite thin film is hardly sufficient. Has a center line roughness Ra of 0.
It exceeds 7 nm and the maximum roughness Rmax exceeds 10 nm.

As shown in FIG. 1, X before and after the plasma treatment
When the line diffraction is compared, the peak of the (311) plane of the magnetite (b) after the plasma treatment is shifted to the wide angle side,
It can be seen that the spacing between the (311) planes is reduced and the structure is changed. In general, it has been found that when changing from magnetite to maghemite having a higher oxidation degree, the spacing between the (311) planes is reduced. From this fact, it is considered that the oxidation is progressing by the plasma treatment.

[0068]

Next, examples and comparative examples will be described.

Examples 1 to 5 and Comparative Examples 1 to 3 A maghemite thin film was obtained in the same manner as in the embodiment of the invention except that the type of target and the plasma treatment conditions were changed.

The production conditions at this time are shown in Table 1, and various properties of the obtained maghemite thin film are shown in Table 2.

[0071]

[Table 1]

[0072]

[Table 2]

Examples 6 to 13 and Comparative Examples 4 to 6: A nickel oxide thin film (thickness: 100 nm) was formed on a glass substrate and then the type of the target was changed. To obtain a magnetite thin film. A maghemite thin film was obtained in the same manner as in the embodiment of the present invention except that the conditions of the plasma treatment were variously changed for the obtained magnetite thin film.

Table 3 shows the production conditions at this time, and Table 4 shows various characteristics of the obtained maghemite thin film.

[0075]

[Table 3]

[0076]

[Table 4]

As can be seen from the examples, when a nickel oxide thin film was formed as a base film and a maghemite thin film was formed thereon, a magnetic recording medium having a smoother surface than that without a base film was obtained. Can be obtained.

[0078]

The magnetic recording medium according to the present invention has a high coercive force and excellent surface smoothness, and thus is suitable as a magnetic recording medium for high-density recording.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern before (a) and after (b) plasma treatment of a magnetite thin film in the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 10/00 H01F 10/00 10/20 10/20 10/30 10/30 41/14 41/14

Claims (4)

[Claims] 1. A magnetic recording medium comprising a substrate and a maghemite thin film formed on the substrate, wherein the maghemite thin film has a thickness of 10 to 50 nm and a center line average roughness Ra of the surface of the maghemite thin film. Is 0.1-0.
A magnetic recording medium having a thickness of 7 nm and a maximum roughness Rmax of 1 to 10 nm. 2. A magnetic recording medium comprising a substrate and a maghemite thin film formed on the substrate, wherein a nickel oxide base film is formed between the substrate and the maghemite thin film, and the thickness of the maghemite thin film is Is 10
A magnetic recording medium having a thickness of 50 nm, a center line average roughness Ra of the surface of the maghemite thin film of 0.1 to 0.7 nm, and a maximum roughness Rmax of 1 to 10 nm. 3. A method for manufacturing a magnetic recording medium, comprising forming a magnetite thin film on a substrate and oxidizing the magnetite thin film to form a maghemite thin film, wherein the magnetite thin film before oxidation is mixed with oxygen gas or a mixed gas containing oxygen. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein plasma processing is performed. 4. Production of a magnetic recording medium in which a nickel oxide base film is formed on a substrate, a magnetite thin film is formed on the nickel oxide base film, and the magnetite thin film is oxidized to become a maghemite thin film. In the method,
3. The method for manufacturing a magnetic recording medium according to claim 2, wherein a plasma treatment is performed on the magnetite thin film before oxidation with oxygen gas or a mixed gas containing oxygen.