JP2701384B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a thin-film magnetic recording medium having excellent durability under normal use conditions.

[Conventional technology]

A thin-film magnetic recording medium is usually manufactured by coating a metal or an alloy thereof on a non-magnetic substrate by coating, plating, vacuum evaporation or sputtering. In actual use, the magnetic head and the magnetic recording medium are worn and damaged by physical contact, that is, sliding. As a result, a number of defects such as an increase in torque due to an increase in the coefficient of friction and a so-called squeal that generates a sound may occur. In addition, the magnetic properties may deteriorate.

As a method for solving the above-mentioned defect, it has been proposed and implemented to provide a protective layer on the magnetic layer. Generally, abrasion largely depends on a mechanical material that slides with an applied external force. Conventional protective films can be roughly classified into (1) carbonaceous films, and (2) fluorination such as modification of carbonaceous films, such as plasma polymerization.
(3) Films other than carbonaceous films, such as oxide films, nitride films, and boride films.

The carbonaceous film (1) has a wide range of structures and physical properties ranging from a diamond-like thin film to an amorphous thin film, and a Hickers hardness ranging from hundreds to thousands. The structure and physical properties of these films obviously depend on the manufacturing method. For example, in the case of a diamond-like carbon film, an ion beam evaporation method, an arc discharge method, and a plasma CVD method are mostly used. However, considering the damage of the magnetic layer at the time of film formation, applying high energy (several hundred eV or more) or excessively increasing the temperature of the magnetic layer at the time of film formation is not preferable because it deteriorates magnetic properties. In addition, it is not advisable to form the protective film by a method completely different from that of the magnetic layer in terms of economy. On the other hand, in the case of an amorphous carbon film, plasma CV using hydrocarbon gas is used.
Manufactured by sputtering using argon gas plasma with D method or graphite as the target. Depending on the manufacturing conditions, some graphite microcrystalline phases may be seen,
Although the existence of sp ³ structures is observed, these are basically amorphous, and in a plasma CVD method, strictly speaking, they are hydrogenated amorphous carbon films. As described above, the structure and physical properties of the carbonaceous film can be changed depending on the manufacturing method and the manufacturing conditions, and this is one of the reasons for being used as a protective film.

Reforming carbonaceous film (2) is carried out by such or using plasma polymerization method, a sputtering method or process gas such as CF ₄ with Teflon target reacted decomposed to a surface treatment. The purpose of this is to obtain physical properties that cannot be obtained with a normal carbonaceous film, for example, to improve water repellency.

There have been many reports of (3) non-carbon films, and the production method is a method of sintering after coating, plasma CVD.
, Sputtering, and reactive sputtering. The purpose is to improve the adhesion with the magnetic layer more than the carbonaceous film, to easily form a harder film than the carbonaceous film, and to improve wear by improving oxidation resistance. It is in.

[Problems to be solved by the invention]

When the magnetic recording medium is used, the disk is rapidly accelerated from the stopped state, and accordingly, the buoyancy is given to the flying head so that the head floats. After use, the power of the motor for rotating the magnetic recording medium is turned off, and the head and the magnetic recording medium physically contact each other. A test in which such an operation is frequently performed to check the durability is called a contact start / stop (hereinafter abbreviated as CSS). In this CSS test, with conventional magnetic recording media, the coefficient of friction increases as the number of CSS cycles increases, and the drive motor stops or the head collides with the protective film within less than several thousand times. Or a head crash that destroys the protective film.

The present invention has been made to solve the above problems, and has as its object to obtain a magnetic recording medium that prevents a large increase in the coefficient of friction and that can be used for many years.

[Means for solving the problem]

The gist of the present invention is to provide a magnetic recording medium having a thin film magnetic layer and a carbonaceous protective layer formed on a nonmagnetic substrate, wherein the carbonaceous protective layer contains 1 atomic% or more of an element of Group 0 of the periodic table. The present invention resides in a magnetic recording medium.

 Hereinafter, the present invention will be described in detail.

In the present invention, an element belonging to Group 0 of the periodic table (hereinafter referred to as a rare gas) is contained in the carbonaceous film which is a protective layer of the magnetic recording medium.
It is characterized by containing.

Noble gases include helium, neon, argon, krypton, xenon, and radon. However, helium is a light element, and has a small atomic radius, resulting in low sputtering efficiency. Radon is a radioactive element and has a short half-life, which makes it difficult to handle. Among the remaining elements, inexpensive argon is most preferable industrially.

The content of the rare gas needs to be 1 atomic% or more in the carbonaceous film. If the content is less than 1 atomic%, the wear rate of the carbon film is high in the sliding process with the head in the CSS test, and the wear powder is seen or the disk is scratched after thousands of CSS times. This may damage the magnetic layer or cause a head crash. In order to further improve the long-term durability, the content of the rare gas is preferably 1.5 atomic% or more, and more preferably 2 atomic% or more. As the rare gas content increases, the durability increases. Tends to improve.

There are several possible methods for causing the carbonaceous film to contain a rare gas. Roughly speaking, (A) a method of containing a rare gas while forming a carbonaceous film, and (B) a method of forming a carbonaceous film after formation. The method can be divided into a method in which a rare gas is injected and contained.
The method (A) includes a plasma CVD method, a sputtering method,
An evaporation method, an ion beam evaporation method, or the like is conceivable. Specifically, in the case of the plasma CVD method, a rare gas is diluted in a hydrocarbon gas and ionized simultaneously in plasma,
A method in which the magnetic layer side is made electrically negative to attract rare gas positive ions, or a method in which rare gas ions are electrically accelerated separately from an ion gun to strike the carbonaceous film being formed on the magnetic layer. And the like. In the case of the sputtering method, a method of intentionally lowering the potential of the carbonaceous film relative to the ions to positively incorporate rare gas ions used for sputtering into the carbonaceous film may be used. Similarly, in the case of the vapor deposition method and the ion beam vapor deposition method, a method of generating a plasma of a rare gas to partially draw ions into a carbonaceous film, a method of supplying a rare gas from an ion source and injecting it into the carbonaceous film, Is mentioned. On the other hand, the method (B) includes a so-called ion implantation method and a similar method.

Here, the argon concentration in the carbonaceous film can be determined by the Rutherford backscattering (RBS) method. Specifically, a carbonaceous film is formed on a substrate of known density, such as silicon single crystal, and the atomic density of each element is compared by comparing the edge heights of the peaks derived from each atom appearing on the RBS spectrum. calculate. Equation (I) gives the edge height of the peak of the RBS spectrum of element A.

In _{^{H A = σ A ΩQNt / cosθ}} A ...... (I) where, H _A is the peak height, sigma _A is the scattering cross section, Omega solid angle of the detector, Q is the ion irradiation amount, N represents the atomic density , T
The film thickness, is θ _A is a rear scattering angle. The ratio between the atomic densities of the elements A and B is as shown in the following equation (II).

N _A / N _B = (H _A / H _B ) · (σ _B / σ _A ) (II) The element B was a sample with a known density, and the present inventors used a silicon single crystal.

As another method, the absolute amount of argon in the film is determined by comparing the X-ray intensity of an unknown sample and a standard sample of argon (which has been implanted with a fixed amount of argon ions by an ion implanter) by X-ray fluorescence analysis. The argon concentration can also be determined from this value and the film density. Both results agree well.

Further, in the present invention, the hardness of the carbonaceous film is 1000 kgf /
mm ² or more. If the hardness is less than 1000 kgf / mm ² , the head tends to be scratched, the wear rate tends to increase, and the wear resistance tends to decrease.

Further, the carbonaceous film is required not only to have abrasion resistance to function as a protective layer, but also to have corrosion resistance to protect the magnetic layer from oxidation. Low-density carbonaceous film has poor corrosion resistance, and in order to block gases that oxidize the magnetic layer such as water vapor,
It is desirable that the carbon film be dense and dense. In the present invention, the density of the carbonaceous film is preferably 1.95 g / cm ² or more. If the density is less than 1.95 g / cm ² , the magnetic layer may be deteriorated.

In the present invention, as the non-magnetic substrate, for example, a non-magnetic metal such as an aluminum alloy or a magnesium alloy, a synthetic resin such as polysulfone, ceramics, glass, or the like can be used which is usually used as a substrate for a magnetic recording medium.

The thin-film magnetic layer is formed on these non-magnetic substrates. Prior to this, a non-magnetic metal thin film such as nickel phosphide may be formed.

The thin-film magnetic layer is formed by depositing a ferromagnetic metal, for example, a cobalt alloy, an iron alloy, or the like on a substrate by a known method such as an electroless plating method or a sputtering method.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist thereof.

Examples 1 to 4 and Comparative Examples 1 to 3 On a 3.5 inch diameter magnetic disk having a cobalt alloy magnetic thin film formed on an aluminum alloy substrate, in an argon atmosphere, at a film forming pressure of 5 mTorr, and at a power density of 3.7 W applied to the target Using a graphite target at / cm ² and changing the negative potential applied to the substrate side in the range of 0 to -150 V,
40 nm thick carbonaceous protective layers with different argon contents were formed by DC magnetron sputtering.

A CSS test was performed using the obtained magnetic disk. C
The SS cycle accelerates the disk rotation to 3600 rpm,
One cycle was protection at 0 rpm for 10 seconds, and stopping for 10 seconds after deceleration by the brake. CSS until the coefficient of friction between the head and disk exceeds 1, or the head or disk is scratched or dirty
The number of cycles was determined. Using a thin film head having a slider of Al ₂ O ₃ .TiC, a test was performed with a pressing load of 15 g. Also, no lubricant was applied on the protective film.

The results are shown in Table 1. For example, when the argon content in the carbonaceous protective layer was 0.2 atomic%, the friction coefficient exceeded 1 in 5000 CSS cycles, and the head crashed in 10,000 cycles.

Examples 5 to 7 On a magnetic disk on which the same cobalt alloy thin film as in Example 1 was formed, a magnetic disk having a carbonaceous protective film having a different argon concentration by increasing or decreasing the negative potential applied to the substrate side by a high-frequency magnetron sputtering method. Was prepared and a CSS test was performed. Negative potential range from -20 to -100V, deposition pressure 5m
Torr, the power density applied to the target was 2.3 W / cm ² , and the other conditions were the same as in Example 1. The results are shown in Table 2.

Examples 8 to 10 and Comparative Example 4 On a magnetic disk on which the same cobalt alloy thin film as in Example 1 was formed, high-frequency power was applied to the substrate side by DC magnetron sputtering, and a magnetic material having a carbonaceous protective film having a different argon concentration was used. A disk was prepared and a CSS test was performed. The range of high frequency power is 5 to 50W, film thickness, film forming pressure,
Other conditions such as the power density applied to the target were the same as in Example 1. The results are shown in Table 3.

Example 11 Argon ions were implanted into a protective film formed in the same manner as in Example 1 by ion implantation at an incident energy of 40 keV and an implantation amount of 1 × 10 ¹⁷ / cm ² by ion implantation. The argon content in the film was about 2 atomic%. A CSS test was performed using the obtained magnetic disk. This film withstood up to 20,000 CSS cycles.

Example 12 and Comparative Examples 5 to 6 In place of argon, a carbonaceous protective film was produced in the same manner as in Example 1 except that the atmosphere was in a xenon atmosphere and the negative potential range was -20 to -80 V. A CSS test was performed on the magnetic disk. The results are shown in Table 4.

Reference Example On a silicon wafer (100) having a diameter of 3.0 inches, a graphite target was used at a power density of 3.7 W / cm ² applied to a target under a deposition pressure of 5 mTorr in an argon atmosphere. , And carbonaceous films having different argon contents were formed by a DC magnetron sputtering method.

Table 5 shows the measurement results of Knoop hardness, internal stress, and density of the obtained carbonaceous film.

Knoop hardness is JIS Z2251 except that the load is 2 g
Was measured based on the microhardness test method.

The internal stress was determined by measuring the warpage of the central portion of the silicon wafer before and after forming the carbonaceous film with a wafer stress gauge manufactured by Ionic System, and calculating the displacement from the following equation.

(Where Σ is the internal stress (dyn / cm ² ), d is the displacement of the center of the silicon wafer, r is the radius of the silicon wafer, E _S is the Young's modulus of silicon, υ is the Poisson's ratio of silicon, and T _S is silicon The thickness of the wafer and T _f indicate the thickness of the carbonaceous film, respectively.) When the argon content in the carbonaceous film is less than 1 atomic%, the hardness is insufficient, and when the argon content is 1 atomic% or more, the internal stress of the carbonaceous film increases and the density also increases. . The reason for this is unknown, but is considered as follows. Argon atoms having high energy collide with the carbonaceous film being formed, which densifies the film being formed. The compressive stress in the film also increases due to the penetration of argon into the film and the reduction of the distance between carbon atoms due to densification. It is recognized that the bulk material is hardened as the compressive stress increases, and it is considered that this sample also hardened as the compressive stress increased. Generally, hardening is recognized to be effective in improving wear resistance, and it is considered that hardening of the carbon film is one of the reasons that the present invention is effective.

〔The invention's effect〕

The problem to be solved by the present invention can be solved by other methods. For example, there is a method of roughening the surface of a magnetic recording medium. However, considering the recording density, it is desirable to reduce the flying distance between the flying head and the magnetic recording medium, and the method of roughening the surface of the magnetic recording medium is not desirable because it is opposite to this direction. There is another method of applying an appropriate lubricant on the protective film. However, depending on the lubricant, the increase in the coefficient of friction may be accelerated, and even if a good lubricant is selected, the life of the lubricant also depends on the protective film. It is still desired.

According to the present invention, a large increase in the coefficient of friction can be prevented. A small increase in the coefficient of friction means that physical and chemical changes due to sliding of the head and the magnetic recording medium are small, and that not only wear resistance but also environmental durability are good. This means that a highly reliable magnetic recording medium can be obtained by the present invention.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a thin film magnetic layer and a carbonaceous protective layer formed on a nonmagnetic substrate, wherein the carbonaceous protective layer contains 1 atomic% or more of Group 0 element of the periodic table. A magnetic recording medium.