JPS61243937A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a frequency characteristic and to prevent the decrease of output by setting the difference between the height at which the area rate in the peak part of a rugged curve of the section of a medium is 1% and the height of the center line of the ruggedness at >=300Angstrom . CONSTITUTION:The area on the line drawn in parallel with the surface of a vertical magnetic recording medium 10 formed with a magnetic Co-Cr film 14 on a heat resistant film 12 in the part of the deepest valley la is made 100% in the rugged curve for the surface roughness at the cut section of said medium. A line is drawn at the peaks 2 at the certain height H and the line H at which the total area of the cut end S of the peaks above the line H is 1% is determined. The difference between the heights of the line H and the average line 3 of the ruggedness is measured. The difference in the height is controlled to >=300Angstrom , by which the frequency characteristic is satisfactorily maintained and the output decrease is prevented.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to perpendicular magnetic recording media.

[Technical Background of the Invention and Problems Therewith] In recent years, perpendicular magnetic magnetization recording methods that perform high-density recording using residual magnetization in a direction perpendicular to the plane of a magnetic recording medium have been attracting attention.

A magnetic recording medium for perpendicular magnetic recording is a medium equipped with a recording magnetic layer that has perpendicular magnetic anisotropy, and is different from the coated media that constitutes most of the magnetic recording media for in-plane recording currently in practical use. Also, metal thin film media in which a thin metal film such as a Co-Cr alloy is formed as a recording magnetic layer by sputtering or vapor deposition, or oxide thin film media with a magnetoplumbite crystal structure such as Ba ferrite or 3R ferrite are highly popular. It is seen as a promising medium more suitable for density recording.

By the way, in coated media, the recording magnetic layer is formed by mixing magnetic powder with a binder etc. and coating it on the substrate, so the recording magnetic layer has elasticity. It is also possible to maintain good contact between the medium and the magnetic head, thereby ensuring sufficient durability of the medium and the head.

On the other hand, in metal thin film media and oxide thin film media, the recording magnetic layer has almost no elasticity, so when a magnetic head made of hard material such as ferrite runs over the media, the surface of the media and head Damage such as scratches is more likely to occur. In this case, not only the durability of the medium and the head is impaired, but also the effective distance between the medium and the head increases due to adhesion of abrasion powder of the medium and the head, resulting in a large spacing loss.

Furthermore, there are several technical challenges in putting into practical use a perpendicular magnetic recording system capable of high-density recording. The main issue is that the adhesion between the surface of the magnetic layer of the medium and the magnetic head must be better than ever. In the perpendicular magnetic recording system, the unevenness of the medium surface tends to cause deterioration in frequency characteristics, as well as a decrease in output and fluctuations in output during reproduction.

[Object of the Invention] The present invention provides a perpendicular magnetic recording medium with good frequency characteristics and no decrease in output.

[Summary of the Invention] In perpendicular magnetic recording media, it is important to solve problems related to frequency characteristics and reduction in output. One of the causes of the deterioration of frequency characteristics and output loss is thought to be that the difference in the height of the surface unevenness of the medium between the lowest output loss level and the signal level has become smaller as density increases. One of the factors that cause signal level fluctuations is the protrusions (irregularities) on the surface of the medium.

Since it is nearly impossible to create a magnetic recording medium with no unevenness on its surface, it is necessary to manage the unevenness in some way. However, the allowable height of unevenness is smaller than that of conventional longitudinal magnetic recording media, and centerline roughness Ra (JIS 8
0601-1982) and the incidence of dropouts.

The same thing can be said about the center surface average roughness assuming the center surface.

One of the reasons for the decrease in output is thought to be that the head rides on a protrusion on the media surface that exceeds the spacing loss, or that the head is unable to come into close contact with the medium after riding on it, creating a gap that exceeds the minimum output loss level. . In this case, it is necessary to clarify how much of the protrusion causes a decrease in output and eliminate it. The present inventors have established a method that allows protrusions that cause output reduction to be described separately from other protrusions.

FIG. 3 shows a cross-sectional view of an example of a perpendicular magnetic recording medium, in which a Go-Crfli film 14 is formed on a heat-resistant film 12 serving as a substrate, and the perpendicular magnetic recording medium 10 is constructed.

FIG. 1 is a curve showing the surface roughness of an example of a perpendicular magnetic recording medium. The part indicated by 1 is called a valley, and the part indicated by 2 is called a peak.If the bottom of the deepest valley 1a in the measurement part is used as the reference line, each point on the medium surface is expressed as its height. I can do it.

Line 3 passing through the average value of the roughness curve can also be used as the reference line. By measuring many of these roughness curves at certain intervals, information about the roughness of the surface can be obtained.

When considering surface roughness using the deepest valley as a reference plane, if you cut parallel to the medium surface at a height H that passes through peak 2, the peaks higher than H will be cut, and peak 2 will have a constant area. A cut S having .

When the area when cutting parallel to the media surface at the deepest valley 1a is taken as 100%, the total area of the cuts is 1%.
It can be cut at a height of 1-1 seconds. The height of the center surface (average surface) of roughness can also be determined by calculation. Here, the number of cuts resulting from cutting at the height of the above-mentioned area ratio of 1% is determined by, for example, spanning and talling a Go-Cr alloy on a substrate made of a heat-resistant organic film. For perpendicular magnetic recording media, the number is 250 to 750 pieces/0.1 mm,
This number is sufficient to support the load of the magnetic head. Therefore, the height Hs at which the total area of the cuts is 1% is considered to be close to the height at which the magnetic head contacts the medium. Therefore, it is considered that the difference between the height H8 at which the area ratio of the cut is 1% and the center plane of the unevenness corresponds to the allowable space length between the head and the medium in magnetic recording/reproduction. In this way, the height of the protrusion of the medium can be defined so as not to reduce the frequency characteristics and reproduction output.

[Embodiment of the invention] A plurality of heat-resistant films whose surfaces are microfabricated with varying degrees of unevenness are prepared, a Co-Cry film is formed by sputtering on the uneven surfaces, and a plurality of perpendicular magnetic recording media are formed. Had made.

Regarding these perpendicular magnetic recording media, when the area ratio of the deepest surface is 100%, the relationship between the height Hs at which the area ratio becomes 1% and the height of the central plane and the relative output was investigated. .

The perpendicular magnetic recording medium evaluated was a 3.5-inch floppy disk, and a ring-type head was used as the magnetic head. As a reference for relative output, a difference of 20 A between the height of the cut area ratio of 1% and the height of the center plane was used.

The unevenness on the surface of the perpendicular magnetic recording medium was measured by using a R = 2JJm diamond stylus (stylus force 30m ()), and fixing the measurement sample on a stern that combined a surface roughness meter with a step motor.
When the stylus measured a certain length, it was returned to its original position, and at the same time, the stage was moved by a step motor to measure roughness in a range of 0.2 mm with a cutoff value of 0.25 mm for each sample. These measurement data were sequentially input into a computer, and after the measurements were completed, necessary corrections were made, such as removing slope and undulation components, and then calculations were performed.

Figure 2 summarizes the measurement results. The horizontal axis shows the difference between the height at an area ratio of 1% and the height of the center plane, and the vertical axis shows the relative output. Curve 4 shows the case where the recording frequency is 50 BPI, and curve 6 shows the case where the recording frequency is 70 KBPI. The difference between the height at which the area ratio of the cut is 1% and the height from the center plane is 30
It is shown that when the relative output is 0 A or more, the relative output is 0.7 or less at BPI of 70, and the same is true at 400 A or more even at 50 KBPI. Therefore, the difference in thickness is preferably
It is considered that 30 OA or less is preferable from the viewpoint of output and frequency characteristics.

In the above-described embodiments, a perpendicular magnetic recording medium having a magnetic layer made of Co-0r was mainly described, but the magnetic layer may be made of other materials. Further, if the Ba Mitsuela unevenness satisfies the conditions specified in the present invention, a perpendicular magnetic recording medium with good frequency characteristics and output characteristics can be obtained.

[Effects of the Invention] As described above, according to the present invention, a perpendicular magnetic recording medium with good frequency characteristics and output characteristics can be obtained by controlling the shape of the surface of the perpendicular magnetic recording medium.

[Brief explanation of drawings]

Figure 1 shows a curve showing the surface roughness of a perpendicular magnetic recording medium to explain the present invention, and Figure 2 shows the difference between the height at which the area ratio of the cut is 1% and the height from the center plane, and the curve at each recording frequency. FIG. 3, which is a diagram showing the relationship with output, is a cross-sectional view of an example of a perpendicular magnetic recording medium. 10...Perpendicular magnetic recording medium 12...Heat-resistant film 14...Magnetic layer agent Patent attorney Noriyuki Chika (other names) No. 1
Figure 3

Claims (1)

[Claims] In a perpendicular magnetic recording medium that has a magnetic layer formed on the surface of a heat-resistant film and has fine irregularities on the surface, the medium surface is cut parallel to the medium surface, and the cutting is performed using the deepest part of the irregular surface as a reference plane. A perpendicular magnetic recording medium characterized in that the difference between the height at which the area ratio of the cut surface of the unevenness is 1% and the height of the central plane of the unevenness is 300 Å or less.