JPS61196424A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To eliminate the disadvantages that the lubricity and corrosion resistance are deficient in a magnetic recording medium using a Co or Co alloy vertically magnetized film and that the recording medium is easy to curl when a high polymer film is used as the substrate by laminating a Co oxide film on the vertically magnetized film. CONSTITUTION:A Co oxide film 3 is formed on a vertically magnetized film 2 by sputtering with Co as the target in an inert gas atmosphere contg. oxygen at specified pressure or by vacuum vapor deposition or ion plating with Co as the vaporization source in rarefied oxygen. Since the Co oxide film 3 has excellent lubricity and corrosion resistance, the head touch and traveling property of a magnetic recording medium are remarkably improved. Moreover, the magnetic recording layer 2 has a columnar fine structure grown in the film-thickness direction and hence the Co oxide film 3 formed on the layer 2 has the same columnar structure. Accordingly, the Co oxide film 3 is structurally and tightly combined with the lower magnetic recording layer 2 and the magnetic recording medium having extremely excellent durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, particularly a magnetic recording medium using a perpendicularly magnetized film.

[Conventional technology]

The perpendicular magnetic recording method can dramatically improve the recording density compared to the current longitudinal magnetic recording method, and its practical application is extremely important for the development of magnetic recording. As recording media for perpendicular magnetic recording, GO and Co-Cr
CO alloys, typified by alloys, and Ba-ferrite have been developed. Ba-ferrite media is produced by dispersing Ba-ferrite fine particles in a binder and coating it on a substrate, and has the advantage of being able to use conventional recording media manufacturing methods, but has the disadvantage of a low saturation magnetic flux density Bs.

[Problem that the invention seeks to solve]

On the other hand, a perpendicularly magnetized film made of CO or Co-gold alloy formed by a thin film deposition method such as a vacuum evaporation method, a sputtering method, or a plating method has a larger Bs than that of Ba-ferrite, and accordingly, higher density recording is possible. However, although the Co or 00 alloy film has excellent magnetic properties, it
Poor wear resistance has traditionally been an obstacle to practical application. As a method to improve this problem, a method of coating the magnetic layer with organic compounds such as metal soap or fatty acid ester perchlorobolyether has been considered, but a protective lubricant with sufficient durability has not been found, and floppy disk In magnetic recording media such as magnetic tapes that use a polymer film as a substrate, warping or curling of the medium causes poor head touch and poor running performance. Since the film is formed by sputtering or the like, a considerable amount of stress remains in the film, which causes the medium to curl.

The present invention eliminates the drawbacks of magnetic recording media using Co or Co alloy perpendicularly magnetized films, such as lack of lubricity and wear resistance, and the drawback that they tend to curl when a polymer film is used as the substrate, and The purpose of the present invention is to provide a magnetic recording medium with excellent durability for density recording.

[Means for solving problems] The magnetic recording medium of the present invention has Co or G on the substrate.

It has a magnetic recording layer of a perpendicularly magnetized alloy film, and is characterized in that a Co oxide film is laminated on the magnetic recording layer.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing the fine structure of a cross section of an embodiment of the magnetic recording medium of the present invention. The magnetic recording medium shown in FIG. 1 has a structure in which a magnetic recording layer 2 of a perpendicularly magnetized film is provided on a substrate 1, and a Co oxide film 3 is further provided on the magnetic recording layer 2.

The substrate 1 is made of glass, aluminum, surface-oxidized aluminum, or a polymer compound such as polyester, polyimide, polyamide, polyacetate, polysulfone, or the like. The magnetic recording layer 2 is composed of a perpendicularly magnetized film made of Co or Co-gold alloy. The magnetic recording layer 2 can be formed using a vacuum evaporation method, a sputtering method, an ion blating method,
Alternatively, it is formed on the base 1 by a plating method. This results in a metal ferromagnetic thin film in which the direction of easy magnetization is approximately perpendicular to the film surface, that is, a perpendicularly magnetized film. As the metal ferromagnetic thin film, Co, Co
-Cr, Co-V, Co-No, Co-W, and Co-Cr-Pd, Co-Or-No, Co-Cr
-Rh, etc. Among them, Co--Cr has a large perpendicular magnetic anisotropy and a perpendicularly magnetized film can be obtained relatively easily. For this reason, the magnetic recording layer 2 is preferably made of Co-Cr.

In addition to being formed directly on the substrate 1, it may be formed with an intervening intermediate layer of a metal film such as Ti, Bi, Ge, etc. or an amorphous film, or between the substrate 1 and the magnetic recording layer 2 or A high permeability magnetic layer may be provided between the substrate 1 and the intermediate layer for the purpose of improving recording efficiency and increasing reproduction output.

The Co oxide film 3 is formed on the perpendicular magnetization $2 by sputtering using Co as a target in an inert gas containing oxygen at a predetermined pressure, or by vacuum evaporation or ion blasting using CO as a deposition source under diluted oxygen. It is formed by C.

This is because the oxide film 3 has extremely excellent lubricity and wear resistance.

Dramatically improves the flat touch and running properties of magnetic recording media. Further, as shown in FIG. 1, the magnetic recording layer 2 has a columnar fine structure grown in the film thickness direction, and the Co oxide film 3 formed thereon also has the same columnar structure. Therefore, the Co oxide film 3 is structurally strongly bonded to the underlying magnetic recording layer 2, resulting in a highly durable magnetic recording medium. Furthermore, the magnetic recording medium of the present invention includes a magnetic recording layer 2 and a Co oxide film 3.
It also has excellent workability because it can be manufactured continuously using the same method.

In the Co oxide film 3, the saturation magnetic flux density Bm changes continuously from ferromagnetic to non-magnetic depending on the oxygen content, and the coercive force Hc also changes, which affects the lower magnetic recording layer 2. Therefore, the Co oxide film The thickness of the W 143 must be determined according to the oxygen content of the W 143 so that the W 143 does not interfere with the recording/reproducing characteristics of the magnetic recording layer 2. In other words, the W 143 has a low oxygen content and has in-plane magnetization.

The oxide film 3 has a large saturation magnetic flux density Ba and a small Ha, so it acts as a magnetic shield layer for the magnetic recording layer 2 below.
When providing the oxide s3 on the upper part of the magnetic recording layer 2, it is necessary to reduce the film thickness.

Furthermore, if the oxygen content is too low, the effects of lubricity and wear resistance will be small, so it is preferable that the Co oxide film 3 has a Bg of 10,000 Gauss or less.

The saturation magnetic flux density of the lower magnetic recording layer 2 is Bsl, the coercive force is Hcl, and the film thickness is δ11 Coi! When the saturation magnetic flux density of the It-based film is Bs2, the coercive force is Ha2, and the film thickness is δ2, δ1Bs1 /He, >δ2 '' 8g2710 /
It is desirable to select 62 so as to satisfy Ha2.

High oxygen content (Co oxide film 3 is non-magnetic or Bg
If this is extremely small, the layer 3 becomes a spacing between the lower magnetic recording layer 2 and the head, reducing recording efficiency and reproduction output. This effect is particularly great on a medium intended for high-density recording, such as the magnetic recording medium of the present invention. Therefore, the thickness of the Co oxide film 3 is preferably 1710 nm or less, which is the shortest wavelength of the recording signal, and more preferably 173 nm or less, which is the shortest wavelength of the recording signal.
It is less than or equal to 0. However, if it is made extremely thin, it will lubricate,
Since the wear resistance effect and durability are poor, it is preferable that the thickness of the Co oxide film 3 is at least 50A or more.

When Co oxide l8I3 becomes a perpendicularly magnetized film, the Co oxide film 3 functions as a magnetic recording layer in the same way as the magnetic recording layer 2, so the thickness of the Co oxide film is not limited to the above range, and even if it is thick. Co oxidation s3 with perpendicular magnetization can be obtained by adding Co so that the initial incident angle of the deposited particles is almost perpendicular to the substrate 1 in an oxygen atmosphere in a certain range or in an oxygen in a certain ratio range to an inert gas. It can be obtained by vapor deposition or sputtering. The oxygen partial pressure at which the perpendicularly magnetized Co oxide film 3 is obtained depends on the manufacturing equipment, but in the case of vapor deposition, it is in 1G-3 torrent of oxygen, and in the case of sputtering, it is in 10 to 20% oxygen in an inert gas. The Bg of the Co oxide film 3, which tends to become a perpendicular magnetization film in the range including It is preferable that the magnetic recording layer 2 does not differ greatly, and it is preferable that both ag and Ha be about the same as those of the magnetic recording layer 2 from the viewpoint of recording and reproducing characteristics.

The lubricity effect of Co oxide l13 depends on the surface unevenness of Co oxide film 3. When the surface unevenness of the layer 3 has a ten-point average roughness RZ (JIS-80801) of 0.005 u or more, the dynamic friction coefficient is 0.3 or less. However, if the maximum value Rmax of the peaks and valleys of the unevenness exceeds approximately 0.05 pm, the signal will be missing in that portion. The surface roughness of the Co oxide film 3 is
Therefore, the surface roughness of the substrate for the magnetic recording medium of the present invention is such that Rz is 0.005 ga or more and Rm
It is preferable that ax is 0.05 μs or less.

It has also been found that when a polymer film is used as the substrate 1, a magnetic recording medium with extremely small curl can be obtained by laminating a Co oxide film 3 on the magnetic recording layer 2. This is a Co film or a G film.

When an alloy film is formed on a polymer film such as polyester, polyimide, or polyamide, the metal film generally curls inward, whereas when a Co oxide film is formed on a polymer film, the Co oxide film curls outward. caused by.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

Example 1 A 40% thick polyimide film was used as the substrate, and 80wt%Ni-20wt%Fe was deposited on it by sputtering.
0.5 scales of the film and 0.3 scales of the 80wt%Co-20wt%Cr perpendicular magnetization film were formed. Furthermore, add 18 oxygen on top of that.
Sputtering Co in Ar gas containing 96
A Co oxide film was formed on the o-Cr film. A sample of this Co oxide film formed directly on a polyimide film under the same conditions was measured with a vibrating sample magnetometer, and the result was that it had no spontaneous magnetization and was nonmagnetic. The thickness of Co oxide film is 0.005゜0
．． 01.0.03. Table 1 shows the recording/reproducing characteristics and durability of 0.11 m floppy disks having the above configuration using a single-side access base vertical head, and shows the results of the 050 and durability of each floppy disk as a guide for short wavelength recording characteristics. It is.

For durability, a floppy disk with no output drop of 3 dB or more and no scratches even after 1 million passes was marked 0. Disk #ILl without a Co oxide film wore out the magnetic layer immediately after head contact and became unusable after approximately 10,000 passes, whereas the disk of the present invention with a Co oxide film 4 and Disk Sui 5 have excellent durability, with no output fluctuation observed even after 1 million passes. The thickness of the Co oxide film is 0.005 g and 0.00 g.
Disks 01-2 and J/L3 were inferior in durability to disks 4 and 5, and output fluctuations occurred after 120,000 and 750,000 passes, respectively. However, in both cases, damage such as the magnetic layer being scraped off, which was observed in the disks, was not observed. The thickness of the Co oxide film should be selected in consideration of the recording wavelength and durability since the recording ability will be lowered.

[Reference example]

80wt%Co-20 was deposited on a 50μs thick polyethylene terephthalate (PET) film by sputtering.
Figure 2 shows the warpage (curl) of the film when a wt% Cr film is formed and when a COs-converted spread film is formed on the film by sputtering, respectively, with respect to the thickness of the film formed on the film. The curl is indicated by the reciprocal of the radius of curvature r, and a positive sign indicates that the film surface is curled inward, and a negative sign indicates that the film surface is curled outward.

Example 2 50, 80wt by sputtering on thick PET film
%Co-20wt%Cr perpendicularly magnetized film of 0.5g was formed, and further Co was deposited on top of it in Ar gas containing 18% oxygen.
By sputtering 0.01.0.03
゜0.05, 0.0? , 0.1 μ of Co oxide films were respectively formed, and five types of floppy disks were manufactured. Figure 3 shows the curl curvature of these floppy disks. *When the Ca-Cr film thickness is 0.5 μs, the curl decreases the most when 0.05 tiles of Co oxide film is formed, and it is sufficiently flat for practical use. A floppy disk was obtained.

Floppy disk without Co oxide film 6 and 0゜05μ
Recording and reproducing experiments were conducted using a ring-type head on the actual floppy disk Sui 7 on which an sCo oxide film was formed.

As a result, the floppy disk 47 of the present invention has a durability of more than 1 million passes, and since the head is in uniform contact with the floppy disk 47, a reproduced output with little output fluctuation within one track can be obtained. On the other hand, in disk Sui 6 without a Co oxide film, the Co-
The Cr film was scraped off within a short time after the head came into contact with it.

Example 3 In Example 2, a floppy disk having the smallest curl was manufactured by changing the oxygen partial pressure during the formation of the Co oxide film. That is, 0.5g of Co-Cr perpendicular magnetization film and 0.05g of Co oxide film were formed on 5O-PET by sputtering method. *The Bg of the Co-Cr film was 5200 Gau.
ss, Hc is 5800e, oxygen is 18%, 18
The Bg of the Co oxide film sputtered in Ar gas containing %, 14%, and 12% is 0 and 1100.48, respectively.
It was 00.7200 Gauss. From the results of measuring the magnetic properties of only the Co oxide film produced under the same conditions, oxygen
% were perpendicularly magnetized films, while the others were nonmagnetic or in-plane magnetized films. Table 2 shows the results of a recording/playback experiment using a ring-type head on these floppy disks.There was no difference in the playback output at long wavelengths for any of the disks, but at 50KBPI output, the disk A9 showed the highest output, and also obtained the largest reproduction output up to short wavelengths. As for durability, no output fluctuations or scratches were observed for any of the disks even after 1 million passes. In this way, when the Co oxide film is a perpendicularly magnetized film, the Co oxide film also functions effectively as a magnetic recording layer, so that the excellent short wavelength recording characteristics of perpendicular recording are not impaired.

Example 4 A 12-thick polyimide film with different surface roughness was used as the substrate L, and Co was deposited by electron beam heating continuous vacuum evaporation method.
A perpendicular magnetization film of 0.42° of 79wt%-Cr21wt% was formed. Furthermore, on top of that, C was added in 6 mTorr of oxygen.
A magnetic tape was produced by forming 0.01 g of O by electron beam heating. The substrate temperature during film formation was 200℃ for both
and the Co-Cr film c7) Bs is 4400 Gauss
, Ha was 9500e, and the Co oxide film prepared under the same conditions was nonmagnetic. The surface roughness of polyimide film measured with Taylor Hobson's Talystep is as follows:
If the ten-point average roughness Rz is less than the measurement accuracy, the maximum roughness Rmax
is 0.02g film! 2: Rz is less than the measurement accuracy, Rm
The ax is 0.18#LII, and the Rz of FILEM Sui 3 is 0.015u.

Rmax is 0.039. , Fillem Sui 4 is Rz
is 0.04JLII.

Rmax is 0.01313g, and Rz of 74 Lum Sui 5 is 0.12g and Rmax is 0.19JAl11.

Table 3 shows the dynamic friction coefficient values of magnetic tapes obtained by forming Co--Cr films and CO oxide films on these polyimide films, the runnability and the number of dropouts when recorded and played back on a VHS deck. Out O is 10 per minute
0 or less, Δ is 101 to 1000, and X is 1001 or more. As shown in Table 3, a tape formed on a very flat film with a very small Rz has a large dynamic friction coefficient and has very poor tape running, and if Rz or Rmax is large, many dropouts will occur8. All of the magnetic tapes of the present invention showed no deterioration in image quality even after 30 minutes of still playback, and had good durability. However, in the magnetic tape without a Co oxide film prepared for comparison, the Co-Cr film was scraped off by the head. It was unplayable. In addition, in the case where there was no Co oxide film, the magnetic tape showed a strong curl with the Co--Cr film inside, but the tape of the present invention with Co oxide formed on the top was sufficiently flat for practical use.

Table 1 〔Effect of the invention〕 As is clear from the above examples, Co or G.

By forming a CO-enriched film on the surface of a magnetic recording medium whose magnetic recording layer is a perpendicularly magnetized film made of an alloy, the wear resistance of the magnetic recording medium has been significantly improved. Furthermore, curling, which was a problem when the substrate was a polymer film, could be removed by adjusting the thickness of the Cos film. Furthermore, if the Co oxide film itself is a perpendicularly magnetized film, it is possible to improve wear resistance and prevent curling without impairing the recording and reproducing ability at short wavelengths.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the magnetic recording medium of the present invention, and FIG. 2 is a diagram showing curling when a Co-Cr film and a Co oxide film are formed on PH7 as a reference example. FIG. 3 is a diagram showing the curl value of the magnetic recording medium of Example 2 of the present invention. 1...Base 2...Perpendicular magnetization film 3...
Co oxide film 4...Curl 5 when forming Co-Cr film...
Figure 1: Curl when Co oxide film is formed

Claims (4)

[Claims] (1) A magnetic recording medium having a perpendicularly magnetized film layer made of Co or a Co alloy on a substrate, characterized in that a Co oxide film is laminated on the perpendicularly magnetized film layer. (2) The magnetic recording medium according to claim 1, wherein the perpendicularly magnetized film layer is made of Co and Cr. (3) The magnetic recording medium according to claim 1 or 2, wherein the Co oxide film is a perpendicularly magnetized film. (4) The magnetic recording medium according to claim 1, 2, or 3, wherein the substrate is a polymer film.