JPH0624055B2 - Perpendicular magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a perpendicular magnetic recording medium. For more details,
The present invention relates to a thin film type perpendicular magnetic recording medium provided with a perpendicular magnetization film mainly composed of cobalt and cobalt oxide and / or iron and iron oxide.

[Prior Art] As a perpendicularly magnetized film constituting a perpendicular magnetic recording medium, an alloy thin film of cobalt and another metal such as cobalt-chromium, cobalt-rhodium, cobalt-vanadium is known as a typical one.

These perpendicularly magnetized films are usually formed on the substrate by sputtering or vacuum evaporation. However, a cobalt alloy film formed by sputtering has a problem that the film formation rate is slow, and it is difficult to control the alloy composition by a method of electron beam vapor deposition of a cobalt alloy. Further, both methods have a drawback that the substrate has to be heated to a high temperature of about 150 ° C. to 300 ° C. in order to obtain a film having good magnetic properties, which is a great obstacle particularly when using a plastic substrate. There is.

As a method of improving such a problem, a method of obtaining a perpendicularly magnetized film composed of cobalt and cobalt oxide on a cooled substrate has been proposed (7th Annual Meeting of the Applied Magnetics Society of Japan).

Further, the present inventors have previously proposed a method of obtaining a perpendicular magnetization film mainly composed of iron and iron oxide on a cooled substrate.

Generally, when putting a thin-film magnetic recording medium into practical use,
Since the magnetic layer rubs directly against the magnetic head, it is extremely important to improve the wear resistance of the medium, that is, to prevent the thin film from being scraped and peeled off. However, a perpendicular magnetization film mainly composed of cobalt and cobalt oxide and / or iron and iron oxide. The inventors of the present invention have found that improvement in wear resistance is essential for practical use even in a magnetic recording medium provided with the above.

Conventionally, as a method for improving the wear resistance of a thin film type magnetic recording medium, firstly, a method of increasing the adhesive force between the thin film and the substrate by pretreatment of the substrate or formation of an underlayer, and secondly, increasing the hardness of the thin film, etc. A third method of modifying the thin film itself is a method of providing a protective layer on the medium surface. In addition, the combined use of these methods and the addition of a lubricant is also being considered.

However, although the first method is effective in preventing peeling,
It has no effect on scraping. The method of increasing the hardness of the second thin film is not preferable because it reduces the flexibility of the medium and deteriorates the contact with the magnetic head, and causes a problem of wear of the magnetic head.

On the other hand, in high density recording, it is important to bring the medium recording layer and the magnetic head as close as possible in order to reduce spacing loss. Therefore, it is desirable not to provide a protective layer.

[Problems to be Solved by the Present Invention] In view of the current state of the prior art, the present inventors have proposed a method of improving wear resistance without increasing contact loss with a magnetic head or the like and increasing spacing loss. As a result of diligent study,
Further, in a perpendicular magnetic film mainly composed of iron and iron oxide, it has been found that these problems can be solved by forming fine projections of a specific structure consisting of a part of the perpendicular magnetic film on the surface, and arrived at the present invention. It is a thing.

[Means for Solving Problems] The present invention has the following configurations.

That is, the present invention is a perpendicular magnetic recording medium provided with a perpendicular magnetization film having magnetic anisotropy in the perpendicular direction on a film surface mainly composed of cobalt and cobalt oxide and / or iron and iron oxide, wherein the perpendicular magnetization film is On the surface, 10 fine protrusions having a tip and a sharp angle of 30 degrees or more and 120 degrees or less are formed.
^The present invention relates to a perpendicular magnetic recording medium having ⁸ pieces / mm ² or more and 2 × 10 ¹⁰ pieces / mm ² or less.

That is, in the perpendicular magnetic recording medium of the present invention, it is important that fine protrusions having a specific tip shape, that is, a specific tip and a sharp edge are formed in a specific density distribution on the surface of the perpendicular magnetization film.

The fine projections forming the surface of the perpendicular magnetization film in the present invention will be described with reference to FIG. FIG. 1 is a model view showing a cross section of an example of the perpendicular magnetic recording medium of the present invention, in which 1 is a substrate and 2 is a perpendicular formed on the substrate 1 in a direction perpendicular to the substrate surface. A fine projection 3 is formed on the surface of the magnetic film. The cross section of the protrusion has a triangular shape, a dome shape, or an intermediate shape between the two, as shown in the figure, and forms unevenness on the surface of the perpendicular magnetization film 1.

Here, the sharp edge angle of the protrusion tip of the perpendicular magnetization film is obtained by the following method as shown in FIGS. 2A, 2B and 2C as a model of various protrusion cross-sectional shapes.

That is, an ultrathin section of the sample medium is prepared, and in the transmission electron microscope image thereof, a perpendicular line A passing through the protrusion 4 and extending in the direction perpendicular to the film surface is drawn, and this is moved in parallel by about 25Å to the left and right. Next, the intersections B ', B "of the obtained perpendiculars A'and A" and the ridgeline B that sandwiches the protrusion 4 are obtained, and tangents C', C "are drawn on each intersection, and these two tangents are drawn. The angle θ formed by is referred to as the sharp angle, and the sharp angle θ is measured for all protrusions within a predetermined distance parallel to the film surface in the transmission electron microscope image, and the average value is used as the sharp angle. is there.

In the present invention, the above-mentioned tip and sharpening angle on the surface of the perpendicular magnetization film are 30 degrees or more and 120 degrees or less, more preferably 50 degrees.
10 ⁸ fine protrusions / m or more and 100 ° or less
m ² or more and 2 × 10 ¹⁰ pieces / mm ² or less, more preferably 4
× 10 ⁸ / mm ² or more and 2 × 10 ¹⁰ pieces / mm ² or less, more preferably 1 × 10 ⁹ pieces / mm ² or more and 1.5 × 10
It is important that the density distribution of ¹⁰ pieces / mm ² or less is present. This makes it possible to effectively reduce the contact area where the medium comes into contact with the magnetic head, tape guide, etc., so that the friction coefficient becomes small. In addition, it is possible to surely reduce the abrasion and to improve the running property between the magnetic head or the tape guide and the medium. In other words, since the specific fine protrusions are evenly present in high density, the contact pressure applied to the part where the load is actually distributed and the contact with the magnetic head is small and the wear is reduced. To be done. In addition, traveling is stabilized, and re-output fluctuation and noise can be reduced.

Further, since the surface area of the medium can be increased, the lubricant is abundantly and strongly adsorbed, so that the wear resistance can be improved.

If the sharpness of the tip of the protrusion is less than 30 degrees, the thin film forming the medium is easily broken, and the spacing loss due to the distance between the magnetic head and the medium increases, which is not preferable. On the other hand, if the sharp angle of the tip of the protrusion exceeds 120 degrees, the wear resistance of the medium is deteriorated and the running property becomes poor, which is not preferable.

Further, if the density of fine projections is less than 10 ⁸ pieces / mm ² , the wear resistance is lowered regardless of the shape of the projections. The density of fine protrusions is 2 ×
When it exceeds 10 ¹⁰ pieces / mm ² , the perpendicular magnetization film itself tends to become non-magnetic, which is not preferable.

As a method of forming fine protrusions on the surface of the magnetic recording medium,
A method is widely used in which fine protrusions are provided in advance on a substrate such as a plastic film, a magnetic layer is formed thereon, and protrusions tracing the protrusions on the substrate are formed on the medium surface.

However, this method has a drawback that the magnetic anisotropy to be oriented in the direction perpendicular to the substrate is disturbed by the projections on the surface of the substrate. For high-density magnetic recording, it is important that there are as many fine protrusions as possible on the medium surface with high density, but with the method of forming protrusions on the substrate surface, it is very difficult to achieve both high density and small protrusions. Have difficulty.

In the present invention, the fine projections derived from the structure of the perpendicular magnetization film are used in combination with the projections formed on the surface of the perpendicular magnetization film by the projections on the substrate surface. It is preferable to reduce the ratio. The protrusions formed by the former method have a high density, a relatively sharp shape, and a large surface area, so that the lubricant is abundantly and strongly adsorbed, and the wear resistance can be further improved.

The perpendicular magnetization film used in the present invention is mainly composed of cobalt and cobalt oxide and / or iron and iron oxide, and has magnetic anisotropy in the direction perpendicular to the substrate surface.

The perpendicular magnetization film having magnetic anisotropy in the direction perpendicular to the film surface according to the present invention is defined as follows.

The magnetic characteristics of the perpendicularly magnetized film can be measured by a vibrating magnetometer method shown in JIS C-2561 or a self-recording magnetometer method. That is, the magnetization (M) of the sample is measured while applying the external magnetic field (H) to the perpendicular magnetization film as the sample.

FIG. 3 schematically shows the measurement result. First, the external magnetic field (H) is gradually increased from the O state (point O), and when the magnetization (M) of the sample is saturated (point A), the external magnetic field (H) is decreased, Further, a magnetic field in the opposite direction is applied. When the magnetization in the opposite direction is saturated (point B), the external magnetic field (H) is reduced, and the external magnetic field (H) in the initially applied direction is applied until the magnetization (M) of the sample is saturated (point A).

The curve of A → B → A obtained in this way is called a hysteresis loop. Magnetic properties such as coercive force and saturation magnetization can be measured from this hysteresis loop. When used in a magnetic recording medium, the larger the area (S) surrounded by the hysteresis loop, the larger the recording capacity and the more suitable for high density recording.

The area surrounded by the hysteresis loop measured while applying an external magnetic field in the direction perpendicular to the perpendicular magnetization film surface of the sample is S
And _⊥, the area of the hysteresis loop of the case of adding an external magnetic field in a direction parallel to the vertical magnetization film layer surface when the S _11, S _⊥
Is larger than S ₁₁ , it can be said that the magnetic recording medium is suitable for magnetic recording in the perpendicular direction.

In the present invention, a perpendicular magnetization film having magnetic anisotropy in the direction perpendicular to the film surface means a hysteresis loop area S _⊥ against an external magnetic field perpendicular to the film surface and a hysteresis against an external magnetic field parallel to the film surface. The magnetic anisotropy coefficient (S _⊥ / S ₁₁ ) calculated from the area S _{11 of the} loop is larger than 1, preferably 1.2 or more and most preferably 1.4 or more.

The thickness of the perpendicularly magnetized film is not particularly limited, but practically a range of 0.02 μm to 5 μm is preferable, and 0.03 μm in particular.
The range of μm to 3 μm, particularly 0.05 μm or 2 μm is most preferable in terms of flexibility and good head touch.

The perpendicular magnetization film is mainly composed of cobalt and CoO, Co.
_It is composed of cobalt oxide and / or iron such as ₂ O ₃ and Co ₃ O ₄ and iron oxide such as FeO, Fe ₂ O ₃ and Fe ₃ O ₄ . As cobalt oxide, besides this,
Non-stoichiometric oxides and peroxides represented by CoOx (X is a number between 0 and 2) are also included. The iron oxide also includes non-stoichiometric oxides and peroxides represented by FeOx (x is a number between 0 and 2).

The perpendicular magnetization film contains cobalt and cobalt oxide and / or iron and an element or compound other than iron oxide, for example,
Nickel, copper, chromium, aluminum, carbon, silicon, vanadium, titanium, zinc, manganese, metal oxides, metal nitrides, metal hydroxides, etc. are included within a range that does not impair the perpendicular magnetic anisotropy. It may be.

Iron and iron oxide are preferably contained in order to make the sharp edges of the protrusions on the surface of the perpendicular magnetization film sharp.

As a method of forming such a perpendicular magnetization film, a vacuum deposition method such as vacuum deposition is adopted.

The perpendicularly magnetized film mainly composed of cobalt and cobalt oxide and / or iron and iron oxide can be obtained by performing vacuum deposition while introducing an oxygen-containing gas into the vacuum chamber. 1 × 10 ⁻⁵ Torr or more, preferably 7 × 10 ⁻⁴ Torr or more and 1 × 10 ⁻² Torr or less, and 20% or more of argon in the oxygen-containing gas,
When an inert gas such as helium or a low activity gas such as nitrogen is introduced, and a part of these gas and vaporized substance is ionized, the tip and the sharp angle formed by a part of the perpendicular magnetic film are 120 on the surface of the perpendicular magnetic film. It is possible to form fine protrusions of less than a certain degree. By setting the substrate or the vicinity of the substrate to a negative potential, it is possible to form a projection having an acute-angled tip. And this tendency is remarkable especially in vacuum deposition.

Another method for forming a fine protrusion having a sharp edge angle of 120 degrees or less on the surface of the perpendicular magnetic film is a method of sputter etching the surface of the preformed perpendicular magnetic film. is there. That is, in the perpendicularly magnetized film sputtered with argon ions or the like, the grain boundary portion is selectively etched, and the remaining portion forms a fine projection having an acute-angled tip. In addition, plasma etching, ion milling, and the like can form fine irregularities, but of course, the present invention is not limited to these methods.

At the time of forming the perpendicular magnetic film, it is desirable that the temperature of the substrate is cooled to 50 ° C. or lower in order to increase the magnetic anisotropy coefficient of the perpendicular magnetic film. In addition, the angle between the vapor of cobalt and / or iron and the normal to the surface of the substrate should be 45 degrees or less.
Providing a mask to block more than one degree of incident particles,
It is preferable for increasing the magnetic anisotropy coefficient of the perpendicular magnetization film.

As a method of ionizing a part of the introduced gas and vapor, a method such as glow discharge, hot cathode excitation, or high frequency excitation can be adopted.

The substrate that can be used in the present invention is not particularly limited.
Aluminum, copper, iron, stainless
Such as metal, glass, ceramic, etc.
Organic materials such as machine materials and plastic films
Can be mentioned. Especially tape, flexible disk, etc.
When processability, formability and flexibility are important, organic polymerization
Suitable body materials, especially polyethylene terephthalate
Polyethylene naphthalate, polyethylene dicarb
Polyester such as xylate, polyethylene, polyp
Polypropylene such as ropylene and polybutene
Lumethacrylate, polycarbonate, polysulfone
Resins, polyamides, aromatic polyamides, polyphenylene
Rufilled, polyphenylene oxide, polyamide
Mido, polyimide, polyvinyl chloride, polyvinyl chloride
Polyvinylidene fluoride, Polytetrafluoroethylene
, Cellulose acetate, methyl cellulose, ethyl cellulose
, Epoxy resin, urethane resin or a mixture of these
Compounds and copolymers are suitable. Especially biaxially stretched
Films and sheets are the most excellent in flatness and dimensional stability.
Suitable, especially polyester and polyphenylene sulphate
Fido, aromatic polyamide, etc. are most suitable.

The shape of the substrate may be any of a drum shape, a disk shape, a sheet shape, a tape shape, a card shape, and the thickness is not particularly limited. In the case of sheet, tape, card, etc., the thickness is 2 to 500 in terms of processability and dimensional stability.
μ, and particularly preferably in the range of 4 to 200 μ.

The substrate used in the present invention may be subjected to various surface treatments and pretreatments for the purpose of facilitating adhesion, improving flatness, coloring, antistatic, imparting abrasion resistance, etc. prior to forming a magnetic film or the like. .

In addition, between the perpendicularly magnetized film and the substrate described in the present invention, it is permissible to laminate one or more underlayers for the purpose of improving the magnetic characteristics of the perpendicularly magnetized film, the corrosion resistance, and the adhesive strength. In particular, providing a soft magnetic film as the underlayer
It is preferable because it has a great effect to increase the recording / reproducing sensitivity.

The perpendicular magnetization film and the underlayer may be formed on either one side or both sides of the substrate.

Further, it is appropriately permitted to laminate one layer or a plurality of layers of a protective layer and a lubricating layer on the perpendicularly magnetized film for the purpose of improving corrosion resistance, abrasion resistance, running property, and the like.

[Advantages of the Invention] According to the present invention, since fine protrusions having a specific tip and a sharp angle are formed on the surface of a perpendicular magnetic film with a specific density distribution, the friction coefficient between the medium and the head is reduced, and the running property is improved. And the wear resistance of the medium could be significantly improved. Further, since the surface area of the magnetized film can be increased, the lubricant can be easily and abundantly and strongly adsorbed, and the wear resistance can be greatly improved.

The perpendicular magnetic recording medium obtained by the present invention is a tape, a sheet,
It can be widely used for magnetic recording of audio, video and digital signals in the form of cards, disks, drums and the like.

[Characteristics Measuring Method / Evaluation Criteria] (1) Magnetic Recording Medium Durability Test Method A test sample in which only one surface of the substrate was processed was punched out into a 5.25 inch floppy disk, and a fluorocarbon lubricant was used. Apply to a thickness of about 200Å and put in a jacket. Using a commercially available floppy disk drive, playback output E when recording and playing after 300 rotations
and _p0, then assess the degree of media wear magnitude of the ratio of the reproduction output E _p1 after being traveling on the same track 100,000 (E _p1 / E _p0). The magnetic head used is a double-sided type head having a pair of button type and gimbal type heads, and the head pressure is about 15 g.

(2) Method for measuring tip and sharp angle of fine protrusion and protrusion density An ultrathin section of a sample medium is cut out and the medium cross-sectional shape is observed by a transmission electron microscope. The magnification is 400,000 times. The sharp angle of the tip of the protrusion is obtained by the following method as shown in the model of FIG. That is, a perpendicular line A passing through the projection top portion 4 and extending in the vertical direction to the film surface is drawn, and this is moved in parallel to the left and right by about 25Å. Next obtained perpendicular A '
And A ″ and intersections B ′ and B ″ between the ridgeline B that sandwiches the protrusion nip 4
Then, the tangents C ′ and C ″ are drawn on each intersection, and the angle θ formed by these two tangents is called the sharp angle, and all are in the direction 5000 Å parallel to the film surface in the transmission electron microscope image. For each of the protrusions, the sharp angle θ is measured, and the average value thereof is used as the value of the sharp angle θ.

The density of the protrusions is calculated by observing the medium surface with a field emission scanning electron microscope. Transmission electron microscope is Hitachi H-
Model 600, field emission scanning electron microscope is Hitachi S-8
Type 00 was used.

(3) Measuring method of magnetic anisotropy coefficient From the area S _⊥ of the hysteresis loop for the external magnetic field perpendicular to the perpendicular magnetic film surface and the area S _{11 of the} hysteresis loop for the external magnetic field parallel to the perpendicular magnetic film surface. The _calculated (S _⊥ / S ₁₁ ) is defined as the magnetic anisotropy coefficient.

It is desirable for the perpendicular magnetization film that the magnetic anisotropy coefficient is larger than 1.

[Example] Example 1 A polyethylene terephthalate film ("Lumirror" manufactured by Toray Industries, Inc.) having a thickness of 50 µm biaxially stretched on a substrate was used.

After evacuating the vacuum chamber to 1 × 10 ^-6 torr, the partial pressure is 4
A mixed gas of oxygen and nitrogen of 0:60 was introduced, the pressure in the vacuum chamber was set to 8 × 10 ⁻⁴ Torr, and iron was evaporated by electron beam vacuum deposition to obtain a thickness of about 0.1 μm at a deposition rate of 10 μm / min.
A perpendicular magnetization film consisting mainly of 25 μm iron and iron oxide was formed on the substrate.

At this time, a tungsten filament was installed in the vicinity of the crucible, heated, and biased at -50 V to irradiate electrons from the filament to ionize the mixed gas and a part of the evaporated material.

The base is placed in close contact with a holder cooled to 5 ° C, and the angle between the iron vapor and the normal to the base is 45 degrees or less.
A water-cooled shield plate that shields incident particles exceeding 45 degrees is installed on the front surface of the substrate.

On the surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film is formed, the tip and the sharpening angle are 70 degrees, and the density is 6 × 10 ⁹ pieces / m 2.
m ² conical fine projections were obtained. The magnetic anisotropy was 1.6.

This medium was punched out into a 5.25-inch diameter floppy disk, and a fluorocarbon lubricant was applied to a thickness of about 200 Å, put in a jacket, and a durability test was conducted.
(E _p1 / E _p0 ) was 1.

Example 2 A perpendicularly magnetized film of cobalt and cobalt oxide having a thickness of about 0.25 μm was formed on the substrate in the same manner as in Example 1 except that the partial pressure of oxygen and nitrogen was 80:20 and the evaporation material was cobalt. Formed.

The surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film is formed has a tip and a sharp angle of 100 degrees and a density of 8 × 10 ⁸ mm ^2.
A small dome-shaped conical fine projection was obtained.
The magnetic anisotropy coefficient was 1.75.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 ) was 0.95.

Example 3 The partial pressure of oxygen and nitrogen is 70:30 and the pressure in the vacuum chamber is 7 × 1.
0 ^-4 Torr, cobalt and iron 80% by weight as evaporation material
In the same manner as in Example 1 except that the alloy No. 20 was used, a perpendicularly magnetized film having a thickness of about 0.25 μm and mainly composed of cobalt, iron and oxides thereof was formed on the substrate.

On the surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film is formed, the tip has a sharp angle of 80 degrees, and the density is 1.9 × 10 ^9.
Cone-shaped fine protrusions of number / piece / mm ² were obtained. The magnetic anisotropy coefficient was 1.68.

A durability test was conducted in the same manner as in Example 1. (E _p1
/ E _p0 ) was 0.98.

Example 4 The gas introduced into the vacuum chamber was 100% oxygen, the evaporate and the gas were not ionized, and the polyimide film biaxially stretched on the substrate had a thickness of 50 μm (“Dupont Co., Ltd.”). In the same manner as in Example 2 except that KAPTON ″) was used, a perpendicularly magnetized film mainly made of cobalt and cobalt oxide and having a thickness of about 0.25 μm was formed on the substrate. On the surface of this perpendicularly magnetized film, unclear protrusions having a sharp edge of 145 degrees and a density of 1 × 10 ¹⁰ particles / mm ² were obtained. The magnetic anisotropy coefficient was 1.36.

This perpendicularly magnetized film sample was placed on the cathode of a high frequency sputtering device (EVP-10758 manufactured by Nichiden Anelva Co., Ltd.), and argon gas was introduced into the vacuum chamber up to 2 × 10 ^-2 Torr.
A current of 13.56 MHz and 100 W was applied to carry out sputter etching with argon ions on the surface of the magnetized film for about 10 minutes.

The surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetization film is formed has a tip sharp angle of 100 degrees and a density of 1 × 10 ^10.
Fine projections of a slightly rounded conical shape with a number of pieces / mm ² were obtained.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 ) was 0.93.

A durability test of the medium before sputter etching revealed that (E _p1 / E _p0 ) was 0.7.

Comparative Example 1 The partial pressure of oxygen and nitrogen was 90:10, and the pressure in the vacuum chamber was 9 × 1.
A perpendicular magnetization film mainly composed of iron and iron oxide was formed on the substrate in the same manner as in Example 1 except that ^0-4 Torr was used.

The surface of the thus-obtained perpendicular magnetic recording medium on the side where the perpendicular magnetic film is formed has a tip sharp angle of 125 degrees and a density of 1.6 × 1.
Dome-shaped concavities and convexities of ⁰⁹ pieces / mm ² were obtained. The magnetic anisotropy coefficient was 1.06.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 ) was 0.78.

Comparative Example 2 Except that the gas introduced into the vacuum chamber was 100% oxygen,
In the same manner as in Example 2, a perpendicularly magnetized film mainly made of cobalt and cobalt oxide and having a thickness of about 0.25 μm was formed on the substrate.

On the surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film was formed, unclear projections having a sharp angle of 140 degrees and a density of 1 × 10 ¹⁰ particles / mm ² were obtained. The magnetic anisotropy coefficient was 1.36.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 ) was 0.65.

Comparative Example 3 Mainly composed of gold, iron and their oxides in the same manner as in Example 3 except that the gas introduced into the vacuum chamber was 100% oxygen and the pressure in the vacuum chamber was 9 × 10 ⁻⁴ Torr. A perpendicularly magnetized film having a thickness of about 0.25 μm was formed on the substrate.

The surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film is formed has a tip sharp angle of 130 degrees and a density of 2.5 × 1.
Unclear projections of ⁰⁹ pieces / mm ² were obtained. The magnetic anisotropy coefficient was 1.15.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 ) was 0.75.

Comparative Example 4 The thickness of cobalt and cobalt oxide was about 0.2 in the same manner as in Example 2 except that ionization was not performed.
A 5 μm perpendicular magnetization film was formed on the substrate.

The surface of the thus-obtained perpendicular magnetic recording medium on the side of the perpendicular magnetization film was obtained from dome-shaped irregularities having a tip and a sharp angle of 145 degrees and a density of 1 × 10 ⁹ pieces / mm ² . The magnetic anisotropy coefficient was 1.7.

When a durability test was conducted in the same manner as in Example 1,
(E _p0 / E _p1 ) was 0.7.

Comparative Example 5 Example except that the pressure in the vacuum chamber was set to 2 × 10 ⁻³ Torr and the polyimide film (“KAPTON” manufactured by Deupon Co., Ltd.) having a thickness of 50 μm biaxially stretched on the substrate was used. In the same manner as in No. 1, a perpendicular magnetic film mainly composed of iron and iron oxide was formed on the substrate. On the surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetization film was formed, sharp fine projections having a sharp angle of 50 degrees and a density of 1 × 10 ¹² pieces / mm ² were obtained.

This perpendicular magnetic film sample was subjected to spatter etching in the same manner as in Example 4 except that the sputter etching time was 20 minutes.

The surface of the perpendicular magnetic recording medium thus obtained on the side of forming the perpendicular magnetization film has a tip and a sharpening angle of 25 degrees and a density of 1 × 10 ¹² pieces /
Very sharp protrusions of mm ² were obtained. The magnetic anisotropy coefficient was 1.1. When this sample was subjected to a durability test in the same manner as in Example 1, (E _p1 / E _p0 was 0.65, which was an unsatisfactory result.

Comparative Example 6 In the same manner as in Example 4 except that the pressure in the vacuum chamber was set at 2 × 10 ⁻⁴ Torr, a 0.25 μm-thick perpendicularly magnetized film mainly made of cobalt and cobalt oxide was formed on the substrate. The surface of the perpendicularly magnetized film has a tip and a sharp angle of 155 degrees,
Unclear projections having a density of 7 × 10 ⁷ pieces / mm ² were obtained. The magnetic anisotropy coefficient was 1.0.

This perpendicular magnetic film sample was subjected to a sputtering process on the surface of the perpendicular magnetic film for 30 minutes by using a high frequency sputtering device in the same manner as in Example 4.

The surface of the perpendicular magnetic recording medium thus obtained on the side where the perpendicular magnetic film is formed has a tip and a sharp angle of 120 degrees and a density of 7 × 10 ⁷ pieces / piece.
A dome-shaped protrusion of mm ² was obtained.

When a durability test was conducted in the same manner as in Example 1,
(E _p1 / E _p0 was 0.50.

[Brief description of drawings]

FIG. 1 is a model diagram of a cross section of a perpendicular magnetic recording medium according to the present invention, FIGS. 2A, 2B, and 2C are explanatory diagrams of a method for measuring the tip and the sharp angle of a protrusion, and FIG. 3 is a measurement example of a hysteresis loop. Is. 1: Medium 2: Perpendicular magnetization film 3: Protrusion 4: Protrusion tip θ: Tip and sharp angle

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium comprising a perpendicular magnetization film having magnetic anisotropy in the perpendicular direction on a film surface mainly composed of cobalt and cobalt oxide and / or iron and iron oxide, the perpendicular magnetization film comprising: On the surface, 30 degrees or more 12
10 ⁸ fine protrusions with a tip and a sharp angle of 0 ° or less
The perpendicular magnetic recording medium characterized by having mm ² or 2 × 10 ¹⁰ pieces / mm ² or less.