JPH0757236A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To obtain a high recording density medium having high coercive force above a prescribed value by laminating a magnetic layer consisting of 1st and 2nd magnetic thin films on an underlayer of Cr, etc. CONSTITUTION:An underlayer 3, a magnetic layer 4 and a protective layer 5 are successively formed on the surface of a nonmagnetic substrate 2. The underlayer 3 is a sputtered film of Cr, W or Mo, the magnetic layer 4 consists of 1st and 2nd magnetic thin films 41, 42 and the substrate 2 is made of a flexible material having <=200 deg.C thermal deformation temp. The 1st magnetic thin film 41 is a sputtered film of a Co-Ni-Cr alloy, a Co-Ta-Cr alloy or a Co-Ni-Ta-Cr alloy and the 2nd magnetic thin film 42 is a sputtered film of a Co-Pt-Cr alloy. The magnetic layer 4 consisting of the thin films 41, 42 has >=1,400Oe coercive force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for in-plane recording having a magnetic thin film formed by sputtering and a method for manufacturing the same, and more particularly to a total of 3.5 inch size flexible disks. The present invention relates to a high-density magnetic recording medium that enables a recording capacity of 200 MB or more and a manufacturing method thereof.

[0002]

2. Description of the Related Art The recording capacity of a 3.5-inch micro floppy disk (MFD), which is the most popular flexible magnetic disk at present, is 1 to 1 disk.
It is 2MB. On the other hand, a hard disk has a 3.5-inch size and reaches 200 MB per disk.
Since compatibility is required in the MFD that prioritizes medium portability, a certain amount of margin is required for tracking the magnetic head, which makes it difficult to achieve high density.
This point can be improved by improving the system. Rather, flexible magnetic disks such as MFD do not have a highly filled magnetic thin film type medium product formed by sputtering like a hard disk, and only a coated type medium using magnetic powder can be manufactured to achieve high recording density. It's a big reason.

In a sputter-type hard disk, an underlayer made of Cr or the like is usually formed on a substrate mainly made of Al alloy, and a magnetic thin film is formed thereon. The composition of the magnetic thin film includes Co-Ni-Cr system, Co-Ta-Cr system,
The Co-Pt-Cr system and many other systems have been adopted. The magnetism of these magnetic thin films is basically due to cobalt. The magnetic characteristics of the magnetic thin film are determined by the type and composition of the magnetic material used, the film forming conditions, etc., and the saturation magnetic flux density is about 5000 to 10000 G and the coercive force is 100.
Magnetic thin films of about 0 to 2000 Oe are used for recording media.

On the other hand, in the longitudinal magnetic recording, increasing the coercive force of the medium is an essential condition for increasing the recording density. In order to obtain a magnetic thin film having a coercive force of 1400 Oe or more, which is one measure for increasing the coercive force, a nonmagnetic layer made of Cr or the like is provided as an underlayer of the magnetic thin film, and (a) Pt is set to 10
˜20 atomic% or more of the magnetic thin film, (b) when the Pt content of the magnetic thin film is about 10 atomic% or less, other additives are added or the magnetic thin film is thinned,
(C) When a system not containing Pt is used for the magnetic thin film,
Basically, various conditions such as heating the substrate to 200 ° C. or higher and thinning the magnetic thin film at the time of forming the magnetic thin film were required.

For example, Japanese Laid-Open Patent Publication No. 3-162710 discloses that as a conventional technique for obtaining a high coercive force of 1200 Oe or more, it is necessary to heat a substrate and the amount of Pt added is 1
It is described that it is necessary to make it about 5 atomic%. Then, in the same publication, by adding P, Pt
Amount of 10 atomic% or less, coercive force of 1400 Oe without substrate heating
The above examples are disclosed. In addition, Japanese Patent Publication
In Japanese Patent Publication No. 49722, Pt amount is 23 atomic%, film thickness is 400
A coercive force of 1400 Oe or more is achieved at A or less. Further, in Japanese Patent Laid-Open No. 62-257617, there is 20
Coercive force values of 1400 to 2400 Oe are shown for Co-Pt alloys containing atomic% Pt.

There are many examples other than these, for example, Japanese Patent Application Laid-Open No. 58-200513 discloses a Co-Pt alloy thin film containing 7 to 40 atomic% of Pt.
When the Pt content before and after is about 50 A, the coercive force is 14
The possibility of achieving 00 Oe has been shown. further,
In JP-A-2-227815, 10 atomic% Pt is used.
By containing 15 to 30 atomic% of oxygen in the Co—Pt alloy thin film containing Pt, a high coercive force of 1400 Oe or more is achieved. These are all conditions (a) and (b) above.
This is a publicly known example of

Known examples related to the above condition (c) include, for example, Journal of Japan Society of Applied Magnetics, Vol. 15, p9.
1, (1991), a substrate temperature of 200
There is an example in which the coercive force of the Co-Ni-Cr / Cr film is increased to 1500 Oe or more by heating to a temperature of ℃ or more. In addition, IEICE Technical Report CPM 89-78
(1989-12-15) shows an example in which the coercive force increases as the magnetic layer becomes thinner at a substrate temperature of 200 ° C., and the coercive force becomes 1550 Oe at a film thickness of 250 A.

[0008]

In order to realize a high coercive force of 1400 Oe or more in a magnetic thin film formed by sputtering, the above-mentioned various means have been devised, and these have been applied to increase the recording density of hard disks. However, since flexible disks are widely used in a large amount due to the portability of the medium, it is particularly important to reduce the cost of the medium. From this point, the amount of Pt required to increase the coercive force of the sputtered film must be kept as small as possible. . In addition, since the flexible film serving as the supporting substrate is also an inexpensive material and has no heat resistance, heating the substrate during sputtering is not preferable.

On the other hand, in order to increase the output of the medium, it is necessary to increase the amount of magnetic flux that carries the signal. In the saturation recording range, the amount of magnetic flux is represented by the product (Br · t) of the residual magnetic flux density (Br) of the medium and the film thickness (t) of the magnetic layer, and the reproduction output increases as this product increases. Therefore, if the magnetic layer is thinned even when an alloy-based material with a high saturation magnetic flux density is used,
This product (Br · t), that is, the amount of magnetic flux is reduced, and the reproduction output is reduced. In order to increase the density of the medium in the future, in particular, to improve the track density, it is necessary to suppress the decrease in the servo information output written on the medium surface.
Securing output in the low range is also important. 25 k as a guide
The FRPI is set to secure an output higher than that of the current metal-coated floppy disk, and experimentally confirmed that a magnetic flux of 250 G · μm (about ² memu / cm ² ) or more is required as the Br · t for this purpose. did. Co-Pt-Cr, Co
In a thin film magnetic material such as -Ni-Cr or Co-Ta-Cr system, Br is generally 500 in a square ratio of 0.7 to 0.85.
0 to 8500 G, and Br · t ≧ 2 in these systems
To obtain 50 G · μm, the film thickness t should be 294-500.
A or higher is required.

Therefore, it is desirable to realize a magnetic layer having a film thickness of at least 300 A or more, preferably 350 A or more, and a coercive force of 1400 Oe or more, while suppressing the amount of Pt used as much as possible. On the other hand, in the condition (a), the amount of Pt used is large, and also in the condition (b), the amount of Pt used is relatively large or the film thickness is less than 300 A. I'm not satisfied. Further, under the condition (c), there is a problem in production such that heating is required.

The present invention has been made under such circumstances, and in a magnetic recording medium having a magnetic layer formed by sputtering, the amount of Pt used in the magnetic layer is significantly reduced to reduce the cost, and at the same time, Br ・ t ≧ 250 G ・
In addition to realizing a sufficient reproduction output of μm, it is possible to use a flexible substrate with low heat resistance by eliminating the need for heating the substrate when forming the magnetic layer, and to provide a high coercive force of 1400 Oe or more. Aim to achieve.

[0012]

These objects are achieved by the present invention described in (1) to (7) below. (1) Cr, W are formed on at least one surface of a non-magnetic substrate made of a flexible material having a heat distortion temperature of 200 ° C. or less.
Alternatively, an underlayer made of a sputtered film of Mo, a first magnetic thin film, and a second magnetic thin film are provided in this order, and the first magnetic thin film is a Co-Ni-Cr alloy or Co-Ta-Cr. A sputtered film of a Co-Ni-Ta-Cr-based alloy, the second magnetic thin film is a sputtered film of a Co-Pt-Cr-based alloy, and the first magnetic thin film and the second magnetic thin film are A magnetic recording medium having a coercive force of 1400 Oe or more in the magnetic layer containing it. (2) The magnetic recording medium according to (1) above, wherein the Pt content of the second magnetic thin film is 2 to 10 atom%. (3) The thickness of the underlayer is 500 to 5000 A, the thickness of the first magnetic thin film is t ₁ , and the thickness of the second magnetic thin film is t _2.
The magnetic recording medium of (1) or (2) above, wherein 100 A ≦ t ₁ ≦ 280 A, 20 A ≦ t ₂ ≦ 280 A, and t ₁ + t ₂ ≧ 300 A. (4) In the magnetic layer, a nonmagnetic intermediate layer is provided between the first magnetic thin film and the second magnetic thin film, and the intermediate layer is C
A metal layer, an alloy layer or an oxide layer containing at least one element selected from the group consisting of r, Mo, V, Nb, Ti and Al, or an oxide layer obtained by oxidizing the first magnetic thin film. The magnetic recording medium according to any one of (1) to (3) above, wherein the thickness of the intermediate layer is 200 A or less. (5) When the residual magnetic flux density of the magnetic layer is Br, the thickness of the first magnetic thin film is t ₁ , and the thickness of the second magnetic thin film is t ₂ , Br · (t ₁ + t ₂ ) ≧ 250 G The magnetic recording medium according to any one of (1) to (4) above, which has a size of μm. (6) A protective layer having a thickness of 50 to 500 A is provided on the second magnetic thin film, and the protective layer is C, SiO ₂ , Al ₂
O ₃ , SiC or Si-Al-O-N (sialon)
The magnetic recording medium according to any one of (1) to (5) above, which is a non-magnetic layer formed of or an oxide layer obtained by oxidizing a second magnetic thin film. (7) A method for manufacturing the magnetic recording medium according to any one of (1) to (6) above, wherein the non-magnetic substrate is not heated when forming the magnetic layer. Method.

[0013]

According to the present invention, by laminating the magnetic layer composed of the first magnetic thin film and the second magnetic thin film on the underlayer composed of Cr or the like, a high coercive force of 1400 Oe or more is obtained. A recording density medium is obtained. In the present invention,
It is only necessary to use Pt for the second magnetic thin film, and
Since the second magnetic thin film is as thin as 20 to 280 A and the Pt content thereof can be suppressed to 10 atomic% or less, the Pt content of the entire magnetic layer can be remarkably reduced. Further, since the heating of the base material when forming the magnetic layer is unnecessary, a flexible base material that is inexpensive but has low heat resistance can be used. In addition, the total thickness of the magnetic layer including the first magnetic thin film and the second magnetic thin film can be sufficiently increased to 300 A or more, so that the reproduction output can be increased. Therefore, a floppy disk having a high recording density like a hard disk and an output equal to or higher than that of the current floppy disk can be obtained at low cost.

By the way, Japanese Patent Laid-Open No. 1-283803 discloses that the magnetic properties can be controlled in a wide range by changing the alloy composition and film thickness of Co-Cr-Pt, and 9% by atom of Pt is contained. An example is shown in which the coercive force of the magnetic layer of Co—Cr—Pt alloy is 1400 Oe or more. However, in this publication, the thickness of the magnetic layer is about 500 to
There is a statement that about 600 A is most preferable in the range of 1000 A. Therefore, P in the magnetic layer described in the above publication
The t content is about twice or more the Pt content of the entire magnetic layer in the present invention, and the object of the present invention cannot be achieved.

[0015]

Concrete Structure FIG. 1 shows a structural example of the magnetic recording medium of the present invention. These magnetic recording media have a non-magnetic substrate 2 surface,
The underlayer 3, the magnetic layer 4, and the protective layer 5 made of Cr are provided in this order. The magnetic layer 4 is composed of a first magnetic thin film 41 and a second magnetic thin film 42 in FIG.
In (b), it is composed of a first magnetic thin film 41, a second magnetic thin film 42, and an intermediate layer 43 provided therebetween. In the illustrated example, a laminated body including an underlayer, a magnetic layer and a protective layer is formed on one surface of the non-magnetic substrate 2, but the present invention has the laminated body on both surfaces of the non-magnetic substrate 2. It also applies to double-sided recording media.

The non-magnetic substrate 2 is flexible and usually made of a resin film. Since it is not necessary to heat the non-magnetic substrate in the present invention, an inexpensive resin film having a heat distortion temperature (Tg) of 200 ° C. or lower, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PE).
N) or the like can be used. The nonmagnetic substrate 2 has various shapes such as a disk shape according to the purpose.

The underlayer 3 is substantially made of Cr, W or Mo.
Is a nonmagnetic continuous thin film formed by sputtering. The underlayer is a hexagonal Co formed on the underlayer.
The c-axis of the first magnetic thin film of the alloy is directed to the inside of the film surface, and it functions to increase the in-plane coercive force of the first magnetic thin film.
This is because the (110) plane of the underlayer having a body-centered cubic structure grows in an orientation parallel to the substrate surface, and on this (110) plane, a crystal plane including the c-axis of the hexagonal Co alloy in the plane. , For example, for the (101) plane to grow epitaxially. As a result, the c-axis, which is the easy axis of the hexagonal Co alloy, is oriented in the plane of the substrate, and the in-plane coercive force increases. The underlayer used in the present invention has a thickness of 500 to 500.
It is preferably in the range of 0 A. If the non-magnetic substrate is not heated, it is difficult to achieve sufficient epitaxial growth if the thickness of the underlayer is less than the above range, and it becomes difficult to set the coercive force of the first magnetic thin film to 1400 Oe or more. When the thickness exceeds the range, the flexibility of the medium becomes low due to the remarkable crystal growth of the metal particles of the underlayer, the head touch becomes defective, and the output fluctuation becomes large. Further, even if the thickness of the underlayer film is increased beyond the above range, the improvement of the magnetic characteristics reaches the ceiling, and the productivity is only reduced.

The first magnetic thin film 41 is Co-Ni-Cr.
Series alloy, Co-Ta-Cr series alloy or Co-Ni-T
It is a continuous thin film composed of an a-Cr alloy, and the easy axis of magnetization is preferentially oriented in the in-plane direction of the film. The specific composition of the first magnetic thin film 41 is not particularly limited, and may be appropriately selected from the composition range in which a high coercive force is obtained.
It is preferable to select i in the range of 20 to 30 atomic%, Cr in the range of 5 to 20 atomic%, and Ta in the range of 1 to 5 atomic%.

The second magnetic thin film 42 is Co-Pt-Cr.
It is a continuous thin film composed of a system alloy. The specific composition of the second magnetic thin film 42 is not particularly limited, and may be appropriately selected from the composition range in which a high coercive force is obtained.
It is preferable to have a composition containing 10 to 10 atomic% and 5 to 10 atomic% Cr.

O, N, Si, Al and M are added to these magnetic thin films as necessary or as inevitable impurities.
Other elements such as n, Ar, B and C may be contained.

In the present invention, when the thickness of the first magnetic thin film 41 is t ₁ and the thickness of the second magnetic thin film 42 is t ₂ , 100 A ≦ t ₁ ≦ 280 A, 20 A ≦ t ₂ It is preferable that ≦ 280 A and t ₁ + t ₂ ≧ 300 A. By controlling the thickness of the first magnetic thin film within the above range, a coercive force of 1400 Oe or more can be achieved without heating the substrate. In this case, in the first magnetic thin film alone is insufficient amount of magnetic flux (Br · t ₁₎ becomes the in possible sufficient cover flux amount of the second magnetic thin film laminated thereto (Br · t _2). However, when the first magnetic thin film has a thickness exceeding the range, high coercive force cannot be obtained, and when the thickness is less than the above range, the amount of magnetic flux is insufficient and it is necessary to thicken the second magnetic thin film. Not preferable.

The reasons for limiting the composition and thickness of the second magnetic thin film will be described. First, when the intermediate layer is not provided between the first magnetic thin film and the second magnetic thin film, if both magnetic thin films have the same composition or the same system, the same result as when the magnetic layer is thickened is obtained. Cannot obtain high coercive force. Further, as described in the above-mentioned CPM 89-78, high coercive force cannot be obtained even when both magnetic thin films are made of Co—Ni—Cr alloy and a Cr intermediate layer is provided between them.
CPM 89-78 describes that stacking enables high coercive force and low noise, but this is premised on substrate heating, and when substrate heating is not performed as in the present invention. , CPM 89-78, the coercive force will decrease if the same magnetic layer is used. This is because it is necessary to make the Cr intermediate layer as thin as 200 A or less in order to avoid an increase in spacing loss, and as a result, the epitaxial growth of the upper magnetic thin film formed with the Cr intermediate layer as the underlayer is incomplete. This is because the coercive force of the upper layer becomes extremely low. Therefore, the second magnetic thin film, which is the upper layer, must be composed of a material having a different composition from that of the first magnetic thin film, which is the lower layer, and having a low dependency on the underlying layer. As a result of the study, it was found that a Co—Pt—Cr alloy thin film having a film thickness within the above range is effective for the second magnetic thin film. In this case, the amount of Pt may be 10 atomic% or less as described above, and the amount of magnetic flux {Br. (T ₁ + t ₂ )} of the entire magnetic layer is 250 within the above film thickness range.
It was found that it can be maintained at G · μm or more. However, if the thickness of the second magnetic thin film is less than the above range, the amount of magnetic flux of the entire magnetic layer cannot be maintained at 250 G · μm or more, and if the thickness exceeds the above range, the crystal growth of ferromagnetic alloy particles occurs. Becomes noticeable and leads to an increase in noise, and expensive P
This is not preferable because the amount of t used increases.

Each magnetic thin film is formed by sputtering. The sputtering method used is not particularly limited, and either DC magnetron sputtering or RF magnetron sputtering may be used. In the present invention, by setting the composition and thickness of each magnetic thin film within the above ranges, high coercive force can be obtained without heating the non-magnetic substrate when forming each magnetic thin film.

When forming the magnetic thin film, as shown in FIGS. 2A and 2B, the line connecting the center of the surface of the target 10 and the center of the surface of the non-magnetic substrate 2 is the surface of the non-magnetic substrate 2. When the angle formed with is φ, it is preferable to perform the sputtering in a state where both are arranged so that the angle φ is 40 degrees or less, preferably 35 degrees or less. At this time,
From the normal state (φ = 90 degrees) in which the central axis of the non-magnetic substrate and the central axis of the target coincide with each other, as shown in FIG. 2B, the non-magnetic substrate 2 may be rotated relative to the target 10 as shown in FIG. 2B.
(A) and (b) may be combined, that is, the nonmagnetic substrate 2 may be moved in parallel with respect to the target 10 and rotated. By setting both of them in such a positional relationship, the particles from the target are obliquely incident on the surface of the non-magnetic substrate. The angle φ when forming the underlayer may be the same as the angle φ when forming the magnetic thin film, but may be different.
A higher coercive force can be obtained by making the target and the non-magnetic substrate have the above-described relationship. Note that the angle φ is more than 0 degrees, but the specific value of the angle φ may be appropriately determined in consideration of the target coercive force, productivity, and the like. When performing sputtering in this way, it is preferable to rotate the non-magnetic substrate. This makes it possible to form the magnetic thin film uniformly and prevent uneven thickness of the magnetic thin film.
It is preferable to rotate the non-magnetic substrate for the same reason when forming the underlayer.

Atmospheric pressure during formation of the magnetic thin film is preferably 0.5 to 5 Pa in order to obtain a high coercive force.
In addition, the atmospheric pressure when forming the underlayer is preferably 1 to 5 Pa. Other sputtering conditions may be appropriately selected from the known range.

The intermediate layer 43 shown in FIG. 1B is a non-magnetic continuous thin film provided to reduce noise. The intermediate layer is a metal containing at least one element selected from the group consisting of Cr, Mo, V, Nb, Ti and Al,
It is preferably an alloy or oxide sputtered film or an oxide layer obtained by oxidizing the first magnetic thin film. The thickness of the intermediate layer is preferably 200 A or less. If the thickness of the intermediate layer exceeds the above range, the spacing loss of the first magnetic thin film becomes large and the reproduction output is lowered, which is not preferable.

The protective layer 5 is a nonmagnetic layer provided to protect the magnetic layer. The protective layer is made of various oxides, nitrides,
It is preferable to be composed of carbide, carbon, silicide, etc., or a mixture thereof, and specifically, for example, C, S
_{iO 2, Al 2 O 3,} SiC, although such Si-Al-O-N (sialon) is preferred, an oxide layer obtained by oxidizing the second magnetic thin film may be a protective layer. The protective layer is usually formed by sputtering. The thickness of the protective layer is generally 50 to
Set to 500 A. If the protective layer is too thin, the protective effect of the magnetic layer is insufficient, and if it is too thick, a reduction in reproduction output due to spacing loss becomes conspicuous.

If desired, a lubricant layer may be formed on the protective layer. The lubricant layer is preferably formed by applying a fluorine-based organic compound or the like.

[0029]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 A polyester film (A4 size) having a surface roughness (Ra) of 17 A and a film thickness of 75 μm was used as a non-magnetic substrate, and a Cr underlayer (film thickness 30) was formed thereon.
00 A), a first magnetic thin film of Co-Ni-Cr alloy (film thickness 250 A), a second magnetic thin film of Co-Pt-Cr alloy (film thickness 250 A) and a carbon protective layer (film thickness 400).
A) was sequentially deposited by sputtering. D for spatter
Using a C magnetron type sputtering device, the initial exhaust was 1 × 10 ⁻⁴ Pa or less, the underlayer was 5 Pa, the first magnetic thin film was 2 Pa, the second magnetic thin film was 5 Pa, and the protective layer was 1 Pa in an Ar atmosphere. Formed by. In the sputtering apparatus, the non-magnetic substrate and the target were arranged as shown in FIG. The angle φ was 42 degrees, and sputtering was performed while rotating the non-magnetic substrate. The non-magnetic substrate was not heated during the film formation. The target was Cr for the underlayer and Co-Ni-Cr (7.5 atomic%) for the first magnetic thin film.
Cr, 30 atomic% Ni) alloy, Co—Pt—Cr (8 atomic% Cr, 10 atomic% Pt) alloy for the second magnetic thin film, and carbon for the protective layer. The diameter of each target was 3 inches.

Then, a lubricant is applied onto the protective layer, and 3.
A 5 inch diameter disc was punched out to obtain a measurement sample. The punching was carried out so that the center of the disc coincided with the center of the polyester film.

Comparative Example 1 Cr underlayer (thickness 3000)
A) magnetic thin film of Co-Ni-Cr alloy (film thickness 500
A) and a carbon protective layer (film thickness 400 A) were formed. The sputtering conditions were the same as those of the underlayer, the first magnetic thin film and the protective layer in Example 1.

Comparative Example 2 A film was formed under the same conditions as in Comparative Example 1 except that the thickness of the magnetic thin film was 250 A.

Comparative Example 3 Cr underlayer (thickness 3000)
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 2
50 A), Cr intermediate layer (film thickness 100 A), Co-Ni-
A second magnetic thin film of Cr alloy (film thickness 250 A) and a carbon protective layer (film thickness 400 A) were sequentially formed by sputtering. The sputtering of the intermediate layer was performed in an Ar atmosphere of 5 Pa, and the other sputtering conditions were the same as in Example 1.

Example 2 Cr underlayer (thickness 3000)
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 2
00 A), Cr intermediate layer (film thickness 100 A), Co-Pt-
A second magnetic thin film of Cr alloy (film thickness 200 A) and a carbon protective layer (film thickness 400 A) were sequentially formed by sputtering. The sputtering conditions were the same as in Comparative Example 3.

Example 3 Cr underlayer (thickness 3000)
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 2
00 A), a second magnetic thin film of Co-Pt-Cr alloy (film thickness 150 A) and a carbon protective layer (film thickness 400 A)
Were sequentially formed by sputtering. However, the angle φ is 3
The target was 0 degree, the target had a diameter of 8 inches, and the same composition as in Example 1 was used, and the sputtering was carried out in an Ar atmosphere of 1 Pa. Other conditions were the same as in Example 1.

Example 4 Cr underlayer (film thickness 1000
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 1
50 A), Cr intermediate layer (film thickness 100 A), Co-Pt-
A second magnetic thin film of Cr alloy (film thickness 250 A) and a carbon protective layer (film thickness 400 A) were sequentially formed by sputtering. Except that the composition of the Co-Pt-Cr alloy target was 8 atomic% Cr, 8 atomic% Pt, and the balance Co, the sputtering conditions were all the same as in Example 3. The intermediate layer was formed in an Ar atmosphere of 1 Pa.

Example 5 Cr underlayer (film thickness 2000)
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 2
00 A), a second magnetic thin film of Co-Pt-Cr alloy (film thickness 200 A) and a carbon protective layer (film thickness 400 A).
Were sequentially formed by sputtering. Except that the composition of the Co-Pt-Cr alloy target was 8 atomic% Cr, 5 atomic% Pt, and the balance Co, the sputtering conditions were all the same as in Example 3.

Comparative Example 4 Cr underlayer (film thickness 1000
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 2
00 A), Cr intermediate layer (film thickness 100 A), Co-Ni-
A second magnetic thin film of Cr alloy (film thickness 200 A) and a carbon protective layer (film thickness 400 A) were sequentially formed by sputtering. The conditions during sputtering were all the same as in Example 4.

Example 6 Cr underlayer (thickness 3000)
A), the first magnetic thin film of Co-Ni-Cr alloy (film thickness 1
50 A), the second magnetic thin film of Co-Pt-Cr alloy (film thickness 250 A) and the carbon protective layer (film thickness 400 A)
Were sequentially formed by sputtering. All sputtering conditions were the same as in Example 3 except that the angle φ was 90 degrees.

The magnetic characteristics and electromagnetic conversion characteristics of the measurement samples obtained in the above Examples and Comparative Examples were measured. The electromagnetic conversion characteristics were measured by pressing a ring head with a gap length of 0.23 μm against the sample and measuring the relative linear velocity of 3.14 m / s.
It was performed under the conditions of. The measurement results are shown in Table 1. In Table 1, the output is the reproduction output value at a linear recording density of 25 kFRPI, and D ₅₀ shows the linear recording density when the output value is halved. Further, the magnetic flux amount Br · t shown in Table 1 is the sum of the magnetic flux amount of the first magnetic thin film and the magnetic flux amount of the second magnetic thin film {Br.
A _{· (t 1 + t 2)} }. For comparison, the measurement results of the current 3.5-inch metal-coated floppy disk are shown. The output shown in Table 1 is a relative output when the output of this metal-coated floppy disk is 0 dB. The magnetic characteristics were measured by VSM at the maximum applied magnetic field strength of 10 kOe.

[0042]

[Table 1]

From Table 1, each embodiment has Br · t ≧ 250 G.
· [Mu] m, satisfies the coercivity ≧ 1400 Oe, the linear recording density as a D ₅₀ of 95kFRPI above, also it can be seen that the current 3.5-inch metal coating type floppy disk and an output of a similar or higher as the output of the low frequency is obtained . From this, the linear recording density is 100 kB by PLL1-7 conversion, for example.
It can be seen that PI is possible and the output is large, so the track density can be 2500 TPI, and 100 MB or more on one side can be secured in terms of recording capacity of 3.5 inches.

[Brief description of drawings]

1A and 1B are cross-sectional views each partially showing a structural example of a magnetic recording medium of the present invention.

FIGS. 2A and 2B are explanatory views showing the relationship between the target 10 and the non-magnetic substrate 2 when forming a magnetic thin film.

[Explanation of symbols]

 2 Nonmagnetic Substrate 3 Underlayer 4 Magnetic Layer 41 First Magnetic Thin Film 42 Second Magnetic Thin Film 43 Intermediate Layer 5 Protective Layer 10 Target

Claims (7)

[Claims] 1. A non-magnetic substrate made of a flexible material having a heat distortion temperature of 200 ° C. or less, on at least one surface of the non-magnetic substrate,
An underlayer made of a sputtered film of Cr, W, or Mo, a first magnetic thin film, and a second magnetic thin film are provided in this order, and the first magnetic thin film is a Co-Ni-Cr-based alloy, Co- Ta-
A sputtered film of a Cr-based alloy or a Co-Ni-Ta-Cr-based alloy, the second magnetic thin film is a sputtered film of a Co-Pt-Cr-based alloy, and a first magnetic thin film and a second magnetic thin film. A magnetic recording medium having a coercive force of 1400 Oe or more in a magnetic layer containing. 2. The Pt content of the second magnetic thin film is 2-10.
The magnetic recording medium according to claim 1, which has an atomic%. 3. When the thickness of the underlayer is 500 to 5000 A, the thickness of the first magnetic thin film is t ₁ , and the thickness of the second magnetic thin film is t ₂ , 100 A ≦ t ₁ The magnetic recording medium according to claim 1, wherein ≤280 A, 20 A ≤t ₂ ≤280 A, and t ₁ + t ₂ ≥300 A. 4. A non-magnetic intermediate layer is provided between the first magnetic thin film and the second magnetic thin film in the magnetic layer, and the intermediate layer is composed of Cr, Mo, V, Nb, Ti and Al. It is a metal layer, an alloy layer or an oxide layer containing at least one element selected from the group consisting of, or an oxide layer obtained by oxidizing the first magnetic thin film, and the thickness of the intermediate layer is 2
The magnetic recording medium according to any one of claims 1 to 3, which has a magnetic field intensity of 00 A or less. 5. When the residual magnetic flux density of the magnetic layer is Br, the thickness of the first magnetic thin film is t ₁ , and the thickness of the second magnetic thin film is t ₂ , Br. (T ₁ + t ₂ ) ≧ The magnetic recording medium according to any one of claims 1 to 4, which has a density of 250 G · μm. 6. The second magnetic thin film has a thickness of 50 to 50.
0 A protective layer, which is C, SiO
_The non-magnetic layer made of ₂ , Al ₂ O ₃ , SiC or Si-Al-O-N (sialon), or the oxide layer obtained by oxidizing the second magnetic thin film. Magnetic recording medium. 7. A method of manufacturing a magnetic recording medium according to claim 1, wherein the non-magnetic substrate is not heated when forming the magnetic layer. .