JPH10289442A - Protective film and magnetic recording medium using the protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize sufficient durability and corrosion resistance even if a film is made thin by providing a protective film comprising a fine grain having equal to or below a specific particle diameter. SOLUTION: Since the grain constituting the protective film has a small particle diameter of <=2 nm, the bonding power between the grains is increased and the omission of grains due to the sliding of a head at the time of CSS (contact start and stop) hardly occurs to improve the durability. And the gap of grain boundary is eliminated since the grains are rigidly arranged each other and the magnetic layer is completely shut out from the atmosphere to keep corrosion resistance excellent under a high temp. and high humidity condition. The film forming method is not limited if the film is formed to ham <=2 nm thickness and the film forming by a sputtering method, a chemical film forming method and the like is possible.

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, and more particularly to a thin-film type magnetic recording medium exhibiting better durability and corrosion resistance than conventional media.

[0002]

2. Description of the Related Art A magnetic recording medium is usually manufactured by forming a magnetic layer by applying a magnetic metal or an alloy thereof on a non-magnetic substrate by coating, plating, vapor deposition, sputtering or the like. By the way, the magnetic recording medium
At the time of actual use, it is worn and damaged by sliding with the magnetic head, and as a result, the friction coefficient is increased and the magnetic characteristics are deteriorated. As a method for solving this drawback, a protective film such as a carbon film, an oxide film, a carbide film, a nitride film or a boride film on the magnetic layer, or a lubricating film such as perfluoropolyether, a higher fatty acid or a metal salt thereof. Has been proposed, and has already been put to practical use.

[0003]

A magnetic recording medium employs a recording / reproducing head which floats by rotation of the medium. When recording / reproducing information, the head does not come into contact with the medium and the medium rotates slowly. Only the method in which the head and the medium come into contact (contact start and stop method,
Some of them adopt the CSS method.

In a durability test of a magnetic recording medium, there is a CSS test in which the flying head is intermittently repeated by controlling the rotation of the medium. However, in the conventional magnetic recording medium, as the number of CSSs increases, the number of CSSs increases. The friction coefficient increases, the surface is damaged by wear, and the head slider does not exert buoyancy for any reason, and the head slides with the medium without floating even during high-speed rotation where the head normally floats. There is a problem that a phenomenon called head crash in which the medium is destroyed occurs.

When used in a high-temperature, high-humidity environment,
In conventional magnetic recording media, the protective layer cannot completely prevent the magnetic layer from being exposed to environmental moisture or oxygen, and the magnetic layer may corrode, causing errors or causing a head crash. was there. In order to suppress this problem, it is conceivable to increase the thickness of the lubricant, but in this case, a meniscus is formed between the head and the disk medium, and there is a problem that the head is easily attracted to the disk. .

Furthermore, it is desired that the protective film be thin for increasing the recording density. In recent years, the thickness of a medium of the order of gigabits per square inch has been reduced to 10 nm or less. For this reason, a problem that the durability and corrosion resistance sufficient for practical use cannot be obtained by simply reducing the thickness of the material used for the conventional protective film having a thickness exceeding 10 nm has begun to surface.

[Means to solve the problem]

An object of the present invention is to provide a protective film that achieves sufficient durability and corrosion resistance even when the thickness is 10 nm or less, and a magnetic recording medium using the protective film. The present inventor paid attention to the microscopic structure of the protective film, and as a result of diligent studies, found that the size of the grains forming the protective film affected the durability and corrosion resistance, and reached the present invention. That is, the gist of the present invention is to provide a protective film composed of grains having a grain size of 2 nm or less and a magnetic recording medium having at least a ferromagnetic metal thin film formed on a nonmagnetic substrate, wherein the grain has a grain size of 2 nm or less. Wherein each of the magnetic recording media has a protective film composed of:

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, the grains constituting the protective film refer to particulates formed by assembling a large number of atoms. Then, the grain is formed, for example, on the protective film by a scanning electron microscope (S
When observed at a magnification of about 100,000 to 300,000 times by EM), grains can be distinguished one by one by a grain boundary which is a boundary between the grains.

Although the grain size of each grain is not exactly the same, in the present invention, several tens of grains are randomly extracted, and the average value of the grain sizes is determined to obtain the grain size of the film. Let it be the particle size.

As a result of measuring a protective film used for a conventional magnetic recording medium, the grain size was as large as 3 nm or more. When the grain size of the grains is large, the bonding force between the grains is small, and the magnetic layer is easily exposed to the atmosphere from the gap between the grain boundaries. Therefore, it is considered that the grains are lost due to the sliding of the head at the time of CSS to increase the friction coefficient, and that under high temperature and high humidity conditions, moisture and oxygen entering from the gaps between grain boundaries corrode the magnetic layer.

Since the grains constituting the protective film in the present invention have a small particle size of 2 nm or less, the bonding force between the grains is increased, and the drop of the grains due to the sliding of the head during CSS is less likely to occur, thereby improving the durability. I do. Further, since the grains are densely arranged, there is no gap between the grain boundaries, the magnetic layer is completely shielded from the atmosphere, and the corrosion resistance under high temperature and high humidity conditions is also good. Grain size is 1nm
The following is preferable in order to further improve CSS durability and corrosion resistance under high temperature and high humidity conditions.

A method for forming a protective film according to the present invention will be described. The method of forming the protective film is not particularly limited as long as the protective film is formed so that the grain diameter of the protective film is 2 nm or less.
D method) and the like. In the sputtering method, the power source such as direct current, alternating current, high frequency, pulse, etc. is not particularly limited, but direct current or high frequency (frequency 13.5
6 MHz) power supply is preferred.

[0013] Carbon is preferable as the main material of the protective film.
In addition, as a gas introduced when sputtering with carbon as a target, Ar, He, H ₂ , N ₂ , O ₂ , hydrocarbons, alcohols, nitrogen-containing hydrocarbons, fluorine-containing hydrocarbons, etc. are not particularly limited, but are preferable. As the introduced gas, Ar as an inert gas, H ₂ as a reactive gas,
Nitrogen-containing hydrocarbons such as N ₂ , hydrocarbons and pyrrole are exemplified. Desirable electric power is 10 to 1000 W.

On the other hand, in the CVD method, DC, AC, high frequency,
The power source such as a pulse is not particularly limited, but a direct current, an alternating current, or a high frequency power source having a frequency of 13.56 MHz is preferable. Desirable power is 10 to 1000 W. Although the type is not limited, such as hot filament, capacitive coupling, inductive coupling, and electron cyclotron resonance, a plasma CVD method using the hot filament, capacitive coupling, and inductive coupling as an ionization source is preferable in order to simultaneously form films on both surfaces of the disk. Considering maintenance and operation rate in industrial production, hot filament plasma CVD is particularly preferable.

The source gases in the CVD method include hydrocarbons such as methane, ethane, propane, ethylene, acetylene, benzene, and toluene, alcohols, nitrogen-containing hydrocarbons,
Any compound containing carbon, such as a fluorine-containing hydrocarbon, can be used, but benzene, toluene, and pyrrole are preferred. An inert gas such as Ar, He, H ₂ , N ₂ and O ₂ may be used in combination.

It is not necessary to apply a bias voltage to the magnetic recording medium on which the protective film is formed, but it is preferable to apply a voltage from the viewpoint of film hardness. Conditions such as gas pressure, power supply voltage, bias voltage, film formation time and the like vary depending on the shape, size, etc. of the apparatus, and thus cannot be particularly limited.
All can be performed under known conditions.

The non-magnetic substrate used for the magnetic recording medium of the present invention is usually Ni-P formed by electroless plating.
An Al alloy plate provided with a layer is used.
A substrate such as a metal substrate such as Ti, a glass substrate, a ceramic substrate, a carbonaceous substrate, or a resin substrate can also be used.

The magnetic layer comprising at least the ferromagnetic metal thin film layer formed on the substrate is formed by a method such as electroless plating, sputtering, and vapor deposition. As this magnetic layer, Co-P, Co-Ni-P, Co-Ni-Cr,
Co-Cr-Ta, Co-Ni-Pt, Co-Cr-P
A ferromagnetic metal thin film such as t, Co-Cr-Pt-Ta alloy is formed, and its thickness is usually about 30 to 70 nm. Further, if necessary, the magnetic layer may have a multilayer structure.

As a layer formed on the substrate, an underlayer or an intermediate layer provided between the ferromagnetic metal thin film layer and the surface of the nonmagnetic substrate can be provided as necessary. As the underlayer, a Cr layer having a thickness of usually 5 to 200 nm formed by sputtering is well known. However, another material may be used, or a plurality of layers may be used. The layer provided on the underlayer is called an intermediate layer, but any material or configuration may be used.

The protective layer according to the present invention is usually provided on the uppermost layer surface of the ferromagnetic metal thin film layer, but may be provided with another layer if necessary. After providing the protective layer according to the present invention, another protective layer may be further provided, or a lubricating layer having a thickness of about 1 to 3 nm may be provided. It is preferable to use a fluorine-based material such as perfluoropolyether for the lubricating layer.

[0021]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. (Examples 1 to 3) First, the average surface roughness was 1.5 nm,
A 3.5 inch diameter NiP plating-coated Al alloy disk substrate is textured (surface treated), and then subjected to sputtering at a substrate temperature of 200 ° C.
Underlayer (thickness: 40 nm), Co alloy magnetic layer (thickness: 50 n)
m) was formed.

Next, the substrate was placed in a plasma CVD apparatus, and the inside of the apparatus was evacuated to 3 × 10 ^-4 Pa by a vacuum pump. Thereafter, toluene was supplied at a flow rate of 3.5 ccm and a pressure of 0.5 ccm.
Introduced into the device at 1 Pa, a current was passed through the filament inside the device to obtain thermoelectrons that would be the ionization source of toluene,
Discharge was caused between the filament and the anode to maintain a stable plasma state. Substrate-filament potential difference is 40
An amorphous carbon protective film was formed while applying a bias so that the voltage became 0V. The thickness of the formed carbonaceous protective film is 5, 1
0, 15 nm. On this protective film, a perfluoropolyether liquid lubricant was applied in a thickness of 2 nm.

When the protective films of the three types of disks obtained were observed by SEM at a magnification of 300,000, the grain size of the grains forming the protective films was 1 nm regardless of the film thickness. A CSS test was performed using the same disk. An MR head having a pressing load of 5 gf was used as the head. After rotating the disk at 4,500 rpm for 5 seconds, turning off the power and allowing the disk to stand for 25 seconds was defined as one cycle of CSS.
The environment during the test is 32 ° C. and 80%. 20,0 CSS
The friction coefficient after repeating the 00 cycle was measured. After the test, the surface of the disk was inspected for scratches and dirt.

As a result, the coefficient of dynamic friction after 20,000 cycles was 1.0 for a film thickness of 5 nm, 0.5 for a film thickness of 10 nm, and 0.5 for a film thickness of 5 nm.
At 15 nm, it was 0.4. In addition, no scratch was observed on the disk surface at any film thickness. Further, the disk was subjected to a corrosion resistance test. It was left in an environment of 85 ° C. and 80% for 2 weeks, and observed for corrosion under a high-intensity lamp. As a result, no corrosion was observed at any film thickness.

(Comparative Examples 1 to 3) For a sample for comparison, an underlayer and a magnetic layer were formed in the same manner as in the example, and a hydrogenated carbon protective film was formed by a sputtering method. The hydrogenated carbon film is formed by mixing a mixed gas of Ar and H ₂ with H ₂
0.5P so that the flow rate of ₂ becomes 14% of the total flow rate.
It was formed by sputtering using a carbon target at a sputtering pressure of a. The thickness of the hydrogenated carbon film was 5, 10, and 15 nm. On this protective film, a perfluoropolyether liquid lubricant was applied in a thickness of 2 nm.

For each of the obtained disks,
When the protective film was observed by SEM in the same manner as in No. 3, the grain size of the grains forming the protective film was 3 nm for a film thickness of 5 nm, 4 nm for a film thickness of 10 nm, and 5 nm for a film thickness of 15 nm. Using this disk, a CSS test was performed in the same manner as in Example 1. As a result, the dynamic friction coefficient after 20,000 cycles was 0.2 at a film thickness of 15 nm,
At a film thickness of 5 nm or 10 nm, a head crash occurred halfway. Further, each disk was subjected to a corrosion resistance test in the same manner as in Example 1. As a result, no corrosion was observed at the film thickness of 15 nm, but corrosion was observed over almost the entire surface at the film thicknesses of 5 nm and 10 nm.

[0027]

As described above, by using the protective film of the present invention, when the film thickness of the conventional protective film becomes 10 nm or less, the CSS durability and the corrosion resistance under high temperature and high humidity conditions were insufficient. On the other hand, even when the film thickness is reduced to 10 nm or less, a large increase in the coefficient of friction and the accompanying head crash are prevented, the corrosion resistance is improved, and a magnetic recording medium having high reliability even at high temperature and high humidity is required. Obtainable. In the embodiments, a hard disk is used as an example, but the protective film of the present invention can be applied to a flexible disk, a magnetic tape, and the like.

Claims (3)

[Claims] 1. A protective film formed by sputtering or CVD and having a thickness of 15 nm or less, wherein the grains forming the protective film have a grain size of 2 nm or less. 2. A ferromagnetic metal thin film is formed directly or through another layer on a nonmagnetic substrate, and a protective film is formed directly or through another layer on the ferromagnetic metal thin film. A magnetic recording medium according to claim 1, wherein the particle diameter of the grains constituting said protective film is 2 nm or less. 3. The magnetic recording medium according to claim 2, wherein a main component of the protective film is carbon.