JPH0311004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic disk medium that is suitable for ultra-high density recording, has high durability, wear resistance, and high reliability. Magnetic recording media for magnetic disk devices, which are generally used as external storage devices for information processing devices, are required to have higher recording density and higher reliability as the amount of information increases. In order to improve the recording density, we need to improve the magnetic properties of the magnetic film attached to the surface of the magnetic disk, such as increasing the coercive force and increasing the magnetic flux density, making the magnetic film itself thinner, and further improving the electromagnetic conversion characteristics. Since it is necessary to reduce the spacing loss by reducing the spacing between the magnetic film of the magnetic head and the magnetic recording medium (hereinafter referred to as spacing), the magnetic film surface must be smooth and free from surface roughness and protrusions. Good things are required. Magnetic disks designed for such high recording densities range from coating-type magnetic films that contain magnetic powder and binder, which have been commonly used, to continuous magnetic films that do not contain binders (continuous magnetic films) that do not contain binders. Because the medium (medium) has a high magnetic storage energy and is advantageous, iron or iron-cobalt alloys are deposited on non-magnetic substrates by sputtering or vapor deposition in vacuum, argon gas, or an atmosphere containing oxygen mixed with argon gas. Continuously deposited ferrite oxide magnetic films (hereinafter referred to as ferrite oxide films) and metal magnetic films have been proposed by various methods. In addition, magnetic films have also been commonly produced by electrodeposition. Magnetic recording media created by these methods are high recording density media with excellent properties. In particular, ferrite oxide films are hard materials and have good corrosive properties, making them difficult to use as magnetic recording media. It is rated as very good. As described above, the properties of magnetic films have been very good for a long time, and magnetic recording media made in this way have sufficient durability and resistance to the sliding of the magnetic head so that they can withstand actual usage conditions. Applying treatments to the surface of magnetic films to improve their abrasion resistance has become an important issue. In other words, in a magnetic disk device, during normal operation, the magnetic head flies above the magnetic film surface of the magnetic recording medium, and the magnetic head does not come into direct contact with the magnetic film, but as the recording density improves, the spacing increases. In order to reduce the size, it is necessary to lower the flying height, and recently a method has been developed in which the magnetic head slides into contact with the magnetic recording medium when the magnetic disk medium starts and stops rotating, that is, the contact start/stop method (hereinafter referred to as the CSS method). ) method is being adopted, so sufficient durability and wear resistance are required. Conventionally, the following methods have been employed to improve the durability and wear resistance of such magnetic recording media. One method is to form a lubricant film directly on the magnetic recording medium to reduce the friction caused by sliding between the magnetic head and the magnetic recording medium. For example, as a lubricant on the surface of a magnetic disk.
By applying a diluted solution of KryToxAD (trademark of DuPont), the surface of the recording medium becomes slippery, which reduces abrasion caused by sliding of the magnetic head and improves abrasion resistance. Since the surface of the magnetic recording medium, that is, the surface of the magnetic film, has very good smoothness, a phenomenon occurs in which the magnetic head is attracted to the recording medium. Here, adsorption refers to the phenomenon in which the magnetic head adheres to the disk surface. This adsorption is a type of adhesion that uses lubricant as an intermediary, and in the CSS method, it is accompanied by stick-slip during sliding contact, which can lead to head crushing in a short period of time, causing damage to the magnetic head and damage to the magnetic surface. This may cause scratches, etc. Applying a lubricant to the surface of a magnetic recording medium in this way reduces the frictional force, but conversely it causes an adsorption phenomenon, so it is not very effective in improving the wear resistance of the surface of the recording medium. I couldn't do it. This head-stag can be reduced by applying a thin layer of lubricant on the magnetic recording medium, but this is not so effective in terms of reducing the frictional force, and if the film thickness of this lubricant is Control is nearly impossible in a mass production process due to the small variable range of film thickness, which results in poor reproducibility and manufacturability. As another method for improving the wear resistance of the surface of a magnetic recording medium, a method of forming a protective film on a magnetic film has been conventionally carried out using a metal magnetic film, and many protective film materials have been proposed. However, in general, the protective film for metal magnetic films has the purpose of improving corrosion resistance in addition to wear resistance, and with a protective film of 300 Å or less, pinholes occur in the protective film, so no effect on corrosion resistance can be expected. Therefore, a protective film with a thickness of 400 Å to 800 Å is normally used. It is also practiced to apply a lubricant on top of this protective film. It is true that the wear resistance of the protective film reaches a practical level, but as mentioned above, when using such a thick protective film, spacing loss becomes a problem and the original performance of the magnetic film cannot be demonstrated. I couldn't do it. Furthermore, even if the protective film were made thin without considering corrosion resistance, if the protective film was less than 400 Å, the wear resistance would be significantly reduced. Therefore, it is an object of the present invention to provide a new magnetic disk medium that eliminates the above-mentioned drawbacks.
By forming an inorganic compound thin film with a thickness of 30 to 200 Å using a vacuum technique such as sputtering, the inorganic compound thin film does not cover the entire magnetic film, but is scattered, and a lubricant film is further applied to the surface. This can be achieved by a magnetic disk medium characterized in that it is formed and configured. The present invention will be explained below based on Examples. FIG. 1 shows the characteristics of the magnetic disk medium according to the present invention, in which the horizontal axis shows the inorganic compound thin film (SiO ₂ ).
The film thickness and the number of sliding movements are shown on the vertical axis. The number of sliding movements is determined by placing an alumina head slider (tapered flat type) on the surface of a magnetic recording medium (disc-shaped) and rotating the medium at a low speed (peripheral speed of 40~
The number of passes through the head until scratches appear on the media surface in an accelerated abrasion test (80 cm/s) is shown. The load on the head is 20 g/mm ² . Therefore, the greater the number of times of sliding, the better the wear resistance. The solid line in Figure 1 shows a dilute solution of KryTox 143AD (DuPont trademark) applied as a lubricant to the SiO ₂ film provided on the magnetic film, and the broken line shows the state without lubrication. show. Furthermore, each line width indicates the variation in measured values. As is clear from the figure, the thicker the SiO ₂ film provided on the magnetic film, the better the wear resistance, regardless of whether it is lubricated or not, and the wear resistance decreases as the SiO ₂ film becomes thinner. In addition, wear resistance is generally lower when not lubricated than when lubricated. What must be noted here is the wear resistance of the SiO ₂ film when the thickness is around 300 Å. When the SiO ₂ film thickness is around 300 Å, there are large variations in wear resistance due to measurement and other factors. Another major feature is that the variation increases when lubricated, and in some measurements, the measured values are lower than when not lubricated. This large variation around 300Å is due to the thinning of the SiO ₂ film.
This is thought to be due to the fact that the strength of the SiO ₂ film decreased significantly and the adsorption effect due to lubrication was added. In order to obtain abrasion resistance at a current practical level, it is necessary that the number of times of sliding is N=2000 or more in this accelerated test. It has been confirmed that this value can withstand more than 20,000 CSS cycles. This condition is stably satisfied when the SiO ₂ film thickness is 400 Å or more during lubrication. Next, we performed detailed measurements of the SiO ₂ film thickness around 300 Å, and the results shown in Figure 2 were obtained. What should be noted here is that the SiO ₂ film thickness is 300 Å.
As in Figure 1, the number of sliding movements N is the lowest, 300.
On the contrary, when the thickness is less than 300 Å, the variation becomes smaller and the wear resistance is improved, and even when the thickness is 300 Å or more, the wear resistance is naturally improved. These reasons are considered to be as follows. When the SiO ₂ film thickness is 300 Å or more, the strength of the SiO ₂ film is high, so it is thought that even if adsorption occurs, it is unlikely to be scratched. Furthermore, when the SiO ₂ film thickness is 300 Å or less, the wear resistance is stable and improved despite the thin SiO ₂ film thickness and low film strength, which is thought to be due to the suppression of adsorption. . In other words, adsorption is a phenomenon of adhesion between the head and the medium using lubricant as an intervening substance, and can be prevented by adjusting the amount of lubricant applied to the medium. The problem here is the adhesion of the lubricant to the medium. As shown in Table 1, it is clear from the good wettability that general lubricants have greater adhesion to inorganic compounds such as SiO ₂ than to magnetic films such as ferrite. Therefore, if a lubricant is applied to a magnetic film on which an inorganic compound is dotted and then thoroughly wiped off, the lubricant can be left only on the surface of the inorganic compound. Therefore, if the amount of inorganic compounds dotted on the magnetic film is increased, the amount of lubricant applied will naturally increase, and conversely, if the amount of inorganic compounds dotted is decreased, the amount of lubricant applied can be reduced. The amount of this inorganic compound is
This can be done by controlling the SiO ₂ film thickness. That is, it is considered that when the SiO ₂ film thickness becomes 300 Å or less, the SiO ₂ film is not attached continuously on the magnetic film, but is already attached in the form of a network to islands. Therefore, as described above, it is possible to control the amount of lubricant applied. Therefore, as shown in Figure 2, when the SiO ₂ film thickness is less than 300 Å, the amount of lubricant applied is controlled and becomes the optimum amount, eliminating adsorption, and improving wear resistance due to the sliding effect of the lubricant. I can do things. Based on this idea, the present inventors were able to control the amount of lubricant applied to the optimum amount and obtain sufficient wear resistance without the need to provide a relatively thick SiO ₂ film called a protective film. We discovered that the optimum film thickness _for this film is 30 to 200 Å, which makes it possible to significantly improve spacing loss while providing sufficient wear resistance for practical use. It was successful.

[Table] FIG. 3 is a diagram showing the relationship between the thickness of the SiO ₂ film provided on the magnetic film and the coefficient of friction (μk) between it and the ferrite head. In the figure, the ○ mark indicates that the SiO ₂ film is not lubricated, and the * mark indicates that it is lubricated. Note that this lubrication is as described above.
This is the case when KryTox143AD is used. As is clear from this figure, during lubrication, a small value of friction coefficient (μk) of 0.15 to 0.19 was obtained when the SiO ₂ film thickness was 30 Å or more. When the SiO ₂ film thickness is in the range of 30 Å to 100 Å, the friction coefficient (μk) is limited by the lubricity of the SiO ₂ film alone.
Although it cannot be less than 0.2, it can be reduced to μk = 0.15 to 0.19 by using a lubricant. The attached table shows the SiO ₂ film thickness on the magnetic recording medium, the coefficient of friction between the magnetic head and the magnetic recording medium with or without lubricant, CSS resistance, property change rate, and sputtering conditions for SiO ₂ film formation. It is. The sample numbers applicable to the present invention are 3 to 9 and 30 to 9.
The measurement results shown in the attached table were obtained for a SiO ₂ film thickness of 200 Å. As is clear from the table, when the lubricant is applied with the film thickness of SiO ₂ of the present invention, the CSS resistance is approximately 20,000 times or more, and the spacing loss (rate of change in characteristics)
was almost 0%, giving very good results. As described above, in the present invention, a film with a thickness of 30 to 200 Å is formed on the magnetic film.
By forming SiO ₂ and applying a lubricant thereon, a magnetic recording medium with no spacing loss and good wear resistance can be provided. In the present invention, a ferrite oxide magnetic film formed by sputtering has been described, but the present invention is not limited to this, and metal magnetic films formed by electrodeposition, sputtering, or vapor deposition may also be used for disks that do not require corrosion resistance.
In addition, it can be applied to non-corrosion-free disks, and even disks that have been subjected to anti-corrosion treatment, as long as the adhesion (bonding strength) between the film that imparts lubricity to the surface, such as silicon dioxide, and the disk surface is good. It is. In addition, as a film that imparts lubricity to the surface, silicon dioxide film (SiO ₂ ), but also the alumina (Al ₂ O ₃ ) film and silicon titanide (Si ₃ N ₄ ) film shown in Table 1 are effective. Furthermore, a silicon dioxide-alumina-beryllium oxide (SiO ₂ -Al ₂ O ₃ -BeO) film can be used simultaneously.
Various lubricants can also be used. <Example> [] Formation of ferrite oxide magnetic film: The surface of an alumina substrate is anodized using a sulfuric acid solution to form an alumite layer with a thickness of 1 to 2 μm. This substrate is then washed and coated with iron containing cobalt. Using target as main component 80% argon (Ar), 20%
Sputtering was performed in an oxygen (O ₂ ) atmosphere to form hematite (α-Fe ₂ O ₃ ) with a thickness of 0.2 μm on the substrate surface. This was heat-treated in a reducing atmosphere to convert it into magnetite (Fe ₃ O ₄ ), and further heat-treated in the air to form a ferrite oxide magnetic film of hematite (γ-Fe ₂ O ₃ ). [] Formation of silicon dioxide film: 100% silicon dioxide as a target on the ferrite oxide film
Argon (Ar) or 80% Argon (Ar) −20
% oxygen (O ₂ ) atmosphere by sputtering. The conditions are shown in the attached table. [] Formation of lubricant film: Apply lubricant A to the rotating disk by spin coating.
KeyTox 143AD (Trademark of DuPont) and K1000 (Trademark of Canion Products) as lubricant B were applied, and then the surface was wiped off with a rotating pad equipped with oil-free paper to form a lubricant film. The lubricant was applied after the silicon dioxide film was formed and left in a desiccator for 20 hours. <Experimental Method> (1) CSS resistance was tested by repeating the cycle shown in Figure 4 and measuring the number of CSS cycles until scratches appeared on the disk surface. Check for scratches by visual inspection. The test was conducted twice for each sample, once on the inner circumference and once on the outer circumference. In addition, the heads used were a winch ester type with a load of 3.2±0.2g, and a taper ferrite type.
A new head was used for each test with Mn-Zu ferrite heads. The rate of change in electromagnetic transmissibility (rate of change in characteristics) is for the samples in the attached table. The output difference is shown in % when the rising wave output in No. 2 without the silicon dioxide film is taken as 1. The head used to measure the characteristics has a flying height of 0.2μ.
Tapered flat type Mn- (peripheral speed 40m/s)
Measurements were made using Zn ferrite using the same head and under the same conditions. Further, the friction coefficient indicates the friction coefficient (μk) immediately after the ferrite head and the magnetic recording medium slide. The friction coefficient values in the attached table are the average values of 5 times. still
The film thickness of SiO ₂ is calculated from the sputter rate, and although it is considered that it is not a completely continuous film if the thickness is less than 200 Å, here it refers to the average shape film thickness calculated by dividing the deposited amount by the total area. be.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the SiO ₂ film thickness and the number of sliding operations, FIG. 2 is a diagram showing the relationship between the SiO _{2 film thickness and the number of sliding operations according to the present invention, and FIG. 4 is a diagram showing the relationship between the SiO 2} film thickness and the number of sliding operations. A diagram showing the conditions for repeating the start and stop of rotation, and FIG. 3 is a diagram showing the relationship between the SiO ₂ film thickness and the coefficient of friction.

Claims (1)

[Scope of Claims] 1. A magnetic disk medium used in a magnetic disk device that records and reproduces information by placing a flying head on a rotating magnetic disk medium, which comprises a magnetic film formed on a substrate, and a magnetic film formed on the substrate. 30 on magnetic film
By forming an inorganic compound thin film with a thickness of ~200 Å using a vacuum technique such as sputtering, the inorganic compound thin film does not cover the entire magnetic film, but is scattered, and a lubricant film is further formed on the surface. A magnetic disk medium characterized in that it is configured as follows.