JPH0770041B2 - Magnetic disk - Google Patents

Description

The present invention relates to an improvement of a magnetic disk used as a storage medium.

[Conventional technology]

The structure of a conventional magnetic disk is shown in FIG. In FIG. 8, 1 is a disc-shaped non-magnetic substrate made of aluminum alloy, 2 is 9-12 μm on the non-magnetic substrate 1 in a chromic acid bath.
The surface roughness of Rm
Non-magnetic hardened layer with ax 0.02 to 0.05 μm and film thickness of 4 to 12 μm, 3 is a neutral method (in Ar), reduction method (Ar + H ₂ ), using a target such as Fe, α-Fe ₂ O ₃ . The Fe ₃ O ₄ film is formed on the substrate by sputtering in a sputtering atmosphere such as the oxidation method (Ar + O ₂ ), or the oxidation method (Ar +
O ₂ ) is sputtered to form an α-Fe ₂ O ₃ film on the substrate, and then a Fe ₃ O ₄ film is formed by hydrogen reduction.
A magnetic recording medium layer _{4 in} which the e ₃ O ₄ film is formed into a γ-Fe ₂ O ₃ film through an oxidation step in the atmosphere is a lubricating layer which covers the magnetic recording medium layer 3.

By the way, in the magnetic disk constructed as described above, even if the recording density is increased, in order to obtain the same read output waveform as in the case of the low density, the thickness of the magnetic layer is reduced to improve the resolution and the recording bit cell 1 In order to prevent a decrease in the read output voltage due to a decrease in the volume of magnetic material per piece, we have adopted a thin film continuous medium formed by sputtering, vapor deposition, etc., in which the magnetic content of the magnetic recording medium layer is increased to 100%. There is.

When the magnetic disk rotates, the magnetic head
Since a so-called contact star stop (CSS) method is used, in which the head floats about 0.1 to 0.3 μm and is in contact with the magnetic head disk when rotation stops, a stable head levitation state at a low flying height is secured and Efforts are being made to prevent disk collisions (head crashes).

Therefore, the conditions of the non-magnetic substrate 1 suitable for high-density recording include good mechanical flatness and surface roughness, small defects, and a small number of defects. Furthermore, as the recording medium becomes thinner, the substrate must have sufficient hardness. That is,
If the board is soft, the magnetic head may deform such as when it comes into contact with the magnetic disk, and the magnetic head cannot be stably floated. Not only will it cause a partial loss of recorded data, which can be said to be a fatal injury as a device, but the number of contact start stops (CSS), which shows the reliability of the magnetic recording device, will decrease, leading to a head crash, resulting in total loss of recorded data. The problem of being connected arises.

In the above description, the problem that occurs due to insufficient substrate hardness has been described. However, even if the substrate hardness is sufficient and the depression does not occur even when the magnetic head and the substrate come into contact with each other, the friction of the lubricating layer 4 is reduced. Is large, the frictional force generated at that time breaks the stable levitating state of the magnetic head, causing a head crash, and there is a problem that data is lost as in the above case.

[Problems to be solved by the invention]

However, the hardness distribution in the cross-sectional direction when an alumite layer is formed on an aluminum alloy that has been conventionally used and polished is as shown in Fig. 9, and the cross-section of scratch marks on the surface of the alumite layer is shown. Is as shown in FIG.

In the case of the conventional substrate in which the alumite layer was formed on the aluminum alloy, the improvement of surface defects such as surface depressions and protrusions was not sufficient as described above.

The present invention has been made to solve the above problems, and an object thereof is to provide a non-magnetic substrate having sufficient hardness and improving surface defects.

[Means for solving problems]

Therefore, the magnetic disk according to the present invention has a non-magnetic hardened layer.
21 is composed of an alloy containing at least nickel and copper having a content of 34 ± 5 WT%, and 300 is formed on this non-magnetic hardened layer.
It is characterized in that the magnetic recording medium layer is formed of a sputtered magnetic film which requires an oxidative heat treatment step at a temperature of ≧ ° for several hours.

[Action]

In the present invention, the alloy containing at least nickel formed on the non-magnetic substrate greatly reduces surface defects such as surface depressions and protrusions of the non-magnetic hardened layer 21. Further, by forming the nonmagnetic hardened layer from an alloy containing nickel and copper having a content of 34 ± 5 WT%, a sputtered magnetic film requiring an oxidation heat treatment step at 300 ° or more for several hours is formed on the nonmagnetic hardened layer. Therefore, even if the magnetic recording medium layer is formed, cracks do not occur in the nonmagnetic hardened layer.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a constitutional view showing an embodiment of the present invention, in which 1,3,4 are the same constituent elements as in the conventional magnetic disk, and 21 is a non-magnetic hardened layer made of an alloy containing at least nickel.

When nickel-phosphorus (Ni-P) is used as the alloy containing nickel, the hardness is relatively high as shown in FIG. 9, and the surface protrusions are greatly improved compared to the conventional alumite coating. I found out that it was done.

As a reason for this, in the case of a conventional alumite coating, a small amount of Mg, Si, Fe or a compound thereof contained in aluminum is present as a hard impurity on the substrate of a soft aluminum alloy, and is a protrusion, whereas It is considered that the substrate is relatively hard with the Ni-P alloy, and even if similar impurities are present, it is processed into a concave shape as a soft substance in the substrate when polished.

Thus, it was found that the Ni-based alloy film is excellent as the nonmagnetic hardened layer 21.

However, among the above steps of the γ-Fe ₂ O ₃ film magnetic disk,
The substrate temperature at the time of sputtering is usually around 240 ° C., and the atmospheric oxidation step for converting γ-Fe ₂ O ₃ requires heating at 300 ° C. or higher for several hours.

Therefore, the magnetism generation temperature of Ni-P plating film is usually 200
Since the temperature is around ° C, the Ni-P plated film is magnetized after the above process.

When the hardened layer becomes magnetized, the magnetic transition width is increased by being recorded in the magnetic medium layer and the hardened layer below this during magnetic recording, and the magnetization of the magnetic medium layer is reproduced by the hardened layer below this during reproduction. Due to the closing, the magnetic flux generated outside the magnetic recording medium is reduced, and there is a problem that the head output is reduced.

Therefore, in order to solve this problem, a Ni-Cu-P ternary alloy plating film showing non-magnetism with a Ni content of 60 wt% or less was considered.

This ternary alloy plating film has a Ni content of 60 as shown in FIG.
It was found that it was non-magnetic at less than wt% and that the hardness was extremely high as shown in FIG.

However, in order to use a γ-Fe ₂ O ₃ sputtered film as a magnetic material, there is an oxidation heat treatment step at 300 ° C. or higher for several hours during the manufacturing process, and it is necessary to endure this heat treatment and it is necessary that cracks do not occur. is there.

However, the initially prototyped disk produced a large number of concentric or radial cracks on the entire disk surface or in the vicinity of the inner and outer peripheral edges in this process, and the problem of insufficient heat resistance became clear.

It was also found that the cracks were classified into concentric circular cracks and radial cracks as shown in FIG. 3, and the sectional structure of the cracks was shown in FIG.

As a result, it is presumed that the cause of cracking in the ternary alloy is stress cracking. In order to eliminate this stress cracking, samples with various Ni, Cu, and P contents were made, and the stress state before and after heat treatment was investigated. did. This investigation was performed by forming a plating film on one surface of a rectangular aluminum plate and measuring the amount of warpage of the plate.

By this investigation, the graph of stress-Cu content shown in FIG. 5 was obtained.

A ternary alloy plating film was formed on both sides of the aluminum foil, and the coefficient of thermal expansion from room temperature to 300 ° C was measured.

As a result, a graph showing the relationship between the copper content and the coefficient of thermal expansion shown in FIG. 6 was obtained.

According to these Fig. 5 and Fig. 6, the Cu content is 34 ± 5 wt.
%, There was no change in stress before and after heat treatment, and the content at this time was found to be equal to the coefficient of thermal expansion of aluminum.

Therefore, with the content of copper (Cu) set to 34 ± 5 wt%, a film of 15-60 wt% with various disk sizes (outer diameter 3 ", 5 1/4", 8 ", 8.8", A film was formed at 9 ″, 10.5 ″), and the crack generation state was examined.

As a result, the graph shown in FIG. 7 was obtained.

From this, it can be seen that the allowable range varies depending on the disk size.

This can be understood in relation to the thermal stress generated by the coefficient of thermal expansion.

As described above, the material of the nonmagnetic hardened layer used in the magnetic disk is composed of nickel (Ni), copper (Cu), and phosphorus (P).
It was concluded that the optimum content of the original alloy and the copper content within the mass ratio of 34 ± 5%.

Although the present invention shows an example in which the aluminum alloy is used as the non-magnetic substrate 1, the same effect can be obtained even if the non-magnetic substrate is made of other metal.

Further, the case where γ-Fe ₂ O ₃ is used as the magnetic recording medium layer 3 has been described, but Co-Ni, Co-Cr, Co-Ni-P, Ba-Fe are used.
rrite, Tb-Fe, it is clear there is no hindrance to apply to Gd-Co, etc. other magnetic, further, SiO _2, Ti on the magnetic
It is clear that there is no problem in application when a protective film of N, SiC, C, etc. is provided.
The effects of high hardness and heat resistance can be obtained.

〔The invention's effect〕

As described above, the present invention comprises a non-magnetic hardened layer made of an alloy containing at least nickel and a copper content of 34 ± 5 WT%, and an oxidation heat treatment step on the non-magnetic hardened layer at 300 ° or more for several hours. Since the magnetic recording medium layer is formed by a sputtering magnetic film that requires, cracks do not occur in the non-magnetic hardened layer even after such heat treatment,
As a product, a high-quality magnetic disk with few surface defects could be obtained.

[Brief description of drawings]

FIG. 1 is a structural diagram of a magnetic disk of the present invention, FIG. 2 is a diagram showing the relationship between nickel content and magnetism, and FIG.
FIG. 4 is a diagram showing a state of cracks in a copper-phosphorus ternary alloy, FIG. 4 is a diagram showing a sectional structure of the crack, FIG. 5 is a diagram showing a relationship between copper content and stress, and FIG. FIG. 7 is a diagram showing the relationship between the content rate and thermal expansion, FIG. 7 is a diagram showing the relationship between the 9-disk size of a non-magnetic substrate and the occurrence of cracks, and FIG. 8 is a configuration diagram of a conventional magnetic disk, FIG. Is a diagram showing hardness distribution of various materials, and FIG. 10 is a cross-sectional view showing a cross section of a scratch. 1 ... Non-magnetic substrate, 2 ... Non-magnetic hardened layer, 3 ... Magnetic recording medium layer, 4 ... Lubrication layer.

Claims (3)

[Claims] 1. A magnetic disk comprising a nonmagnetic substrate coated with a nonmagnetic hardened layer, the coated nonmagnetic hardened layer coated with a magnetic recording medium layer, and the magnetic recording medium layer coated with a lubricating layer. In the above non-magnetic hardened layer, at least nickel and the content rate of 34 ± 5 W
The magnetic recording medium layer is formed of an alloy containing T% copper, and the nonmagnetic hardened layer is formed with a sputtering magnetic film requiring an oxidation heat treatment step at 300 ° or more for several hours. Magnetic disk to do. 2. The magnetic disk according to claim 1, wherein the nonmagnetic hardened layer is formed of a ternary alloy in which phosphorus is mixed with an alloy of nickel and copper. 3. The magnetic disk according to claim 1 or 2, wherein the nickel content is 60 WT% or less.