JPS62219223A - Thin metallic film type magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance while maintaining durability by providing a protective layer formed by oxidizing a Co-Al alloy on a magnetic Co alloy layer. CONSTITUTION:This recording medium has a nonmagnetic substrate 1, the magnetic layer 2 consisting of a Co alloy film, and the protective layer 3 formed by partially oxidizing the Co-Al alloy. The quantity of Al atoms contained in the protective layer 3 is adequately 5-35% as the ratio of the number of Al atoms per the total number of Co atoms and Al atoms and is further preferably 20-35%. The thickness of the protective layer 3 is adequately 30-300Angstrom and the more preferable range is 50-100Angstrom . The effect of protection is not enough if the thickness is <=30Angstrom . Recording and reproducing characteristics are deteriorated by a spacing loss if the thickness exceeds 300Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a metal thin film magnetic recording medium that has excellent durability and corrosion resistance.

[Prior Art] In recent years, there has been a strong demand for higher density magnetic recording, and various research and development efforts are underway. metal? ;i
One of these methods is a method using a magnetic layer of a film. Among these, the method using a perpendicularly magnetized film is considered to be a method suitable for increasing the density because self-demagnetization approaches zero as the density increases.

The materials for the magnetic layer used in this metal thin film magnetic recording medium are mainly Go, Go-Ni, and Go-P.

Go-Ni-P, Co-Cr, Go-V, (:o
-No, Go-Pt, Go-W.

Go-Or-Pd, Co-Cr-Ha, Go-Cr
Co-based alloys such as -Rh are being studied. One of the major problems with magnetic recording media with such metal magnetic layers is that they lack a significant amount of wear resistance, with direct contact between the magnetic layer and the magnetic head causing scratches on both. .

This problem is an important problem related to the reliability of magnetic recording media, but conventional methods for solving this problem include using fatty acids, higher fatty acids, oxyfatty acids, fatty acid amides, fatty acid esters, fatty alcohols, and metal soaps. etc. have been applied to the surface. However, with the above method, it is difficult to make the thickness of the top coat layer uniform, and its effectiveness deteriorates as it is used.

It was not satisfactory because it lacked durability.

As a method to improve this point, forming a protective layer of cobalt oxide has been carried out. As a means of film formation, vapor deposition method (for example, JP-A-5Ei-137528, JP-A-80-
191425, etc.), reactive sputtering method (e.g. 4.
501322) has been proposed.

However, the above protective layer has problems in terms of corrosion resistance.
For example, if recording or reproduction is performed after being left under high temperature and high humidity conditions, the reproduction signal may be degraded or missing. This corrosion resistance itself can be improved considerably by increasing the degree of oxidation, but
In this case, the durability deteriorates and it is not possible to achieve both performances. This point poses a major problem in practice.

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the above-mentioned problems of the prior art and provide a metal thin film magnetic recording medium that has excellent durability and corrosion resistance.

[Means and effects for solving the problems] The present invention has the following features:
A magnetic layer made of an alloy containing Co as one component is provided on at least one surface of the nonmagnetic substrate, and a Co-Al! The present invention is a metal thin film type magnetic recording medium characterized by having a protective layer made of an oxide of an alloy, thereby achieving the above object.

FIG. 1 shows the basic structure of the metal thin film magnetic recording medium of the present invention. l is a non-magnetic substrate, 2 is a magnetic layer made of a Go alloy film, and 3 is a partially oxidized Co-AR alloy. It is a protective layer. As the nonmagnetic substrate 1, a plastic film made of polyethylene terephthalate, polyimide, polycarbonate, polyamide, etc., stainless steel, aluminum, glass, etc. can be used. Materials for the magnetic layer 2 include Co, Co-Cr, Go-
V, Go-No.

Co-W, Go-P, Go-Ni, Go-Pt,
Go-Xi-ρ, Go-Cr-Ru.

Alloys such as Go-Cr-Rh and Go-Cr-Mo can be used.

In addition, the metal thin film magnetic recording medium of the present invention includes, for example, an intermediate layer between the substrate and the magnetic layer for the purpose of improving adhesion and controlling surface roughness, and a high permeability layer that is effective when using a perpendicular head. A magnetic layer or the like may be provided. Further, a coating of fatty acid, higher fatty acid, oxyfatty acid, fatty acid amide, fatty acid ester, aliphatic alcohol, metal soap, etc. may be provided as a lubricating layer on the oxide protective layer. Furthermore, it is also possible to provide a layer for lubrication or antistatic purposes on the back surface of the substrate.

In addition, a structure in which magnetic layers, protective layers, etc. are provided on both sides of the substrate is also possible.

The properties that the protective layer should have are that it does not easily adhere to the head material, and therefore has good lubricity, and at the same time, it protects the underlying Co.
It must be strongly adhered to the alloy magnetic layer and must not be difficult to peel off.

The Go-based oxide is excellent as a protective layer for CO3O.
4 (spinel structure) has solid lubricity, and the decrease in surface cohesiveness is largely affected. However,
In the case of a completely oxidized protective layer, at the interface with the 1m layer,
The metal phase and oxide phase (mainly CO3O4: spinel structure) of the c, p, structure are in contact with each other, and the crystal lattice of the two is difficult to match, so the bond between the two is weak, and the protective layer is damaged by sliding with the head. Easy to peel off. Therefore, in order to obtain a durable protective layer, it is preferable that some metal phase remains in the protective layer, and it is presumed that this remaining metal phase is responsible for improving the adhesion with the magnetic layer. be done.

Corrosion is caused by oxidation of this metallic phase. In contrast, in the present invention, the metal phase is Go-AI! It is an alloy and has higher corrosion resistance than Co alone, so even if the metal phase remains, the corrosion resistance effect can be obtained.

Note that if the content of Ai) is excessive, the durability will decrease. The reason for this is that Go-AI! of the b, c, c structure within the metal phase! It is conceivable that the ordered lattice phase becomes dominant and the bonding force at the interface with the magnetic layer decreases, or that a small amount of Ai'203 phase is generated near the surface.

As a result of the above consideration, the amount of AP atoms contained in the protective layer is Aj) relative to the total number of Go atoms and i atoms.
The ratio of the number of atoms is preferably 5 to 35%, more preferably 20 to 35%.

Further, as a result of various studies, the thickness of the protective layer is preferably 30 to 300A, and a more preferable range is 50 to 100A. Below 30A, the protective effect is not sufficient;
If it exceeds this, the recording and reproducing characteristics will deteriorate due to spacing loss.

Although the present invention is a technology that can be applied to CO-based alloy magnetic films in general, it is better to use non-oriented or obliquely-oriented magnetic layers when the C-axis of the magnetic layer (macrogonal system) is oriented in a direction perpendicular to the medium surface. Even when the protective layer was somewhat thinner, the durability tended to be relatively good. This is probably due to the difference in the ease of achieving crystallographic consistency between the magnetic layer and the metal phase in the protective layer. The C-axis is perpendicular to the medium surface, and the present invention is particularly effective for Co-based alloy perpendicular magnetic recording media. In particular, it has been reported that when a perpendicular magnetic recording medium is used in combination with a ring head, the spacing loss is greater than in the longitudinal magnetic recording method, and better adhesion between the magnetic layer and the magnetic head is required. (The 9th Japanese Society of Applied Magnetics, Academic Lecture Summary Collection P, 100'), and the present invention, combined with its high-density recording property, exhibits remarkable effectiveness in perpendicular magnetic recording media that require fFj protective films.

Furthermore, according to recent technical trends in research and development, it is generally easier to obtain a high-quality magnetic film when the Go alloy metal magnetic layer is formed by a physical vapor deposition process in a vacuum, such as a vacuum evaporation method or a sputtering method. For example, in the case of an in-plane magnetized film such as a Co-X1 alloy film, in order to increase its coercive force, an oxygen-introducing evaporation technique is often used at the same time as oblique evaporation, and a surface oxide layer is also created at that time (for example, Showa 58-4
No. 1439).

At this time, some oxidation occurs to the inside of the magnetic material, so if you try to strongly oxidize the outermost surface, the inside of the magnetic layer will actually be oxidized.
This results in a decrease in Bg, resulting in a decrease in recording and reproducing characteristics (for example, Japanese Patent Application Laid-Open No. 191425). For in-plane recording media with relatively low recording densities, this method can have sufficient practicality, and the present invention provides, for example, the film forming method disclosed in the above-mentioned publication, in which vapor that participates in the formation of a surface layer is used. It can be realized in such a manner that a vapor flow of a metal containing AR is merged with a vapor flow of a metal containing AR. On the other hand, due to the high recording density used in the CO-based perpendicular magnetization film, it is necessary to reduce spacing loss as much as possible. It is advantageous if the steps are separated.

The present invention provides a thin oxidation protective film that is highly durable and wear-resistant, does not impair the magnetic properties of the magnetic layer, and has good corrosion resistance. It can be suitably used in perpendicular recording media used in the short wavelength region.

[Example] Hereinafter, description will be given based on an example. Note that the results here are obtained when the thickness of the protective layer was approximately 10 OA in both Examples and Comparative Examples.

Example 1 A polyimide resin film with a thickness of 10 JLm was used as a nonmagnetic substrate, and a Co-Cr alloy film with a thickness of 0.4 lu was continuously deposited thereon to obtain a long sample.

A protective layer of Ca-/j) oxide film was formed on this sample by a reactive sputtering method using the apparatus shown in FIG.

4 is a vacuum chamber, 5 is an exhaust device, and 6 is a Go-AP alloy target, which is connected to an external high-frequency power source. A sample film 7, in which a Co-Cr alloy layer was previously formed on a polyimide film by vacuum evaporation, was transferred from an unwinding roll 8 to an intermediate free roller 9. drive can 10,
It passes through the intermediate free roller 9 again and reaches the winding roll 11. 12 is an adhesion prevention plate, 13 is an oxygen introduction pipe, and 14 is an argon introduction pipe.

The ultimate pressure during film formation was 3 x 104 Pa or less, the Ar gas pressure was 0.30 Pa, the amount of oxygen introduced was 8 cc/min, and the input power per unit area was 4 W/c+a2. At this time, the deposition rate was about 20 A/sec, and the sample film driving rate was 15 cm/min.

Example 2 Polyethylene terephthalate 12 pm thick, f
After forming a Go--Ni--P alloy layer with a thickness of 0.4 lum on the substrate of the lume by plating, a Go--Ai) alloy oxide protective layer was formed in the same manner as in Example 1.

Example 3 On the same substrate as in Example 1, a Go-
After forming the Pt alloy layer by vacuum evaporation method, Example 1
Similarly, Co-Al! A protective layer of oxide film was formed.

Example 4 The same Co-C as in Example 1 was deposited on the same substrate as in Example 1.
After forming the r alloy layer, Go-AP is applied using the apparatus shown in Fig. 3.
A protective layer of oxide film was formed by vacuum evaporation.

The overall structure is almost the same as the device shown in FIG.

Oxygen is introduced into the vacuum chamber through an introduction pipe (not shown).

A part of the vacuum chamber is partitioned by a partition wall 15, and the inside thereof is evacuated by another exhaust device 16. An electron gun 17 is installed in this small room, and the Go-AP alloy pellets 19 in the crucible 18 are heated by the electron beam emitted from it. The purpose of providing the partition wall is to maintain the interior at a high vacuum to prevent damage to the electron gun due to oxygen inflow.

The ultimate pressure is 5 x 1 (15 Pa or less, the amount of oxygen introduced is 1
2 cc/min, the deposition rate is about 500 A/sec, and the sample film feed rate is 3.5 m/min.

Example 5 After forming a similar Go-Cr alloy layer on the same substrate as in Example 1, Go-AI! forming a layer of alloy,
This surface was subjected to plasma oxidation using the apparatus shown in FIG. 4 to form a protective layer. The sample is passed through oxygen plasma generated between the electrodes 20 to perform plasma oxidation.

The conditions are vacuum degree 0.30 Pa, oxygen partial pressure 0.08 Pa, input power 300 W, and sample film feeding speed 40 c.
m/min.

Comparative Examples 1 to 5 Examples 1 to 5 except that the protective layer did not contain AR and was made of GO oxide
Samples prepared in the same manner as in Comparative Examples 1 to 5
And so.

Comparative Example 6.7 Comparative Examples 6 and 7 were samples prepared in the same manner as in Example 1 and Example 4, except that a Co--Af oxide containing 40% AJ was used as the protective layer.

Table 1 shows the A of the protective layer for the above Examples and Comparative Examples.
j) Results of content, durability and tactility tests are shown. However, AI! The content is AR'fX with respect to the number of metal (i.e. Go+Ai) atoms contained in the protective layer.
Indicates the ratio of the number of children.

Durability tests were carried out on the samples of the above examples and comparative examples for 8 m.
After cutting into II width and making it into a tape, commercially available 8 mmV
This was done using a TR deck. The method involved recording a test pattern and repeatedly playing it back to examine changes in head output and number of dropouts depending on the number of passes. The criteria for determining durability are as follows. If the output decreases on the 100th pass of repeated playback is within 3 dB of the initial output, A,
3 dB or more was rated B, and a case where the number of dropouts exceeded 200 per minute before reaching 100 passes was rated C.

In addition, the method of counting dropout is 18dB from the average output.
It was counted as one piece when the above decrease in output continued for 15g seconds or more.

Corrosion resistance test was performed using sample tape prepared in the same manner as above.
After leaving it in a constant temperature and humidity chamber at 0° C. and 70% humidity for 50 hours, recording and playback were attempted using the same deck as above. A indicates that there was no problem at all, and B indicates that there was an increase in dropouts in the outermost 30cm portion of the tape while the tape was left unused, but no other problems occurred.B indicates that normal output was obtained over the entire tape. C refers to the parts that appear repeatedly.
1. A tape in which the portion that can be recorded and reproduced normally was 20% or more of the total length of the tape was designated as D.

Tables 1 and 2 also show the test results for durability and corrosion resistance. However, the sample in this case was formed into a disk shape using the same material and approximately 50 pm thick film as the substrate in the above-mentioned Examples and Comparative Examples, and had a 50 kB thickness.
This is a recording and reproduction of the PI signal.

The criteria for determining durability are A if the output decreases after 1 million passes within 3 dB compared to the initial output, B if it is 3 dB or more, and C if stable playback output cannot be obtained.

The criteria for determining corrosion resistance were as follows: After being left under the same conditions as described above, recording and reproducing were attempted, and those with no problems were rated A, those with output loss were rated B, and those with no stable output were rated C.

Table 2 [Effects of the Invention] As explained above, Co-Aj on the CO-based alloy magnetic layer
By providing a protective layer formed by oxidizing the l' alloy, it was possible to significantly improve the corrosion resistance while maintaining durability equivalent to or higher than in the case of providing a conventional protective layer.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram showing the basic structure of the gold IA thin film magnetic recording medium of the present invention, Figure 2 is a schematic diagram of the high frequency sputtering apparatus used to form the protective layer, and Figure 3 is a schematic diagram of the high frequency sputtering apparatus used to form the protective layer. The vacuum evaporation device used for the formation, and FIG. 4 shows the plasma oxidation device used to oxidize the protective layer. 1: Non-magnetic substrate, 2: Co-based alloy magnetic layer, 3: Ca-A
R oxide protective layer, 4: Vacuum chamber, 5: Exhaust device, 6: Co
-Aj) Alloy tarp-/), 7: Sample tape, 8
: a release roll, 9: intermediate free roller, 10: drive can, ll: take-up roll, 12: adhesion prevention plate, 13: oxygen introduction pipe, l4: argon introduction pipe, 15: tE4 wall, 16: exhaust device, 17 = electron gun, 18 nil acupuncture point, 19: Co-A
R alloy pellet, 20: electrode, 21: capacitor, 2
2: High frequency power supply, 23: Earth.

Claims (2)

[Claims] (1) A metal thin film characterized by having a magnetic layer made of an alloy containing Co as a main component on at least one surface of a nonmagnetic substrate, and a protective layer made of an oxide of a Co-Al alloy thereon. type magnetic recording medium. (2) The metal thin film type magnetic recording medium according to claim 1, wherein the magnetic layer is provided with anisotropy so that the magnetization is aligned in a direction perpendicular to the plane of the medium.