JPH11175960A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film magnetic recording medium having a Co-alloy magnetic layer formed on a plastic nonmagnetic substrate, and to provide a thin film magnetic recording medium having improved corrosion resistance of the magnetic layer and excellent durability. SOLUTION: This magnetic recording medium is produced by forming a Co-alloy magnetic layer 4 on a plastic nonmagnetic substrate 1, and further forming a carbon protective film 5, and a lubricating layer 6 thereon. The carbon protective film 5 consists of a first protective film 5A comprising a hydrogen-contg. amorphous carbon and a second protective film 5B comprising a hydrogen-free amorphous carbon and a hydrogen-contg. amorphous carbon having a smaller hydrogen content than in the first protective film or a nitrogen- contg. amorphous carbon prepared by incorporating nitrogen into the hydrogen- contg. amorphous carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film magnetic recording medium having a Co non-magnetic magnetic layer provided on a plastic non-magnetic substrate.

[0002]

2. Description of the Related Art As an external recording device for a computer,
Hard disks are generally widely used. The recording capacity of recent hard disks has been increasingly increased, and several gigabits / square inch have been put to practical use.

Conventional hard disks are made of glass or Ni-
This is a type in which a thin-film type magnetic layer such as a Co alloy-based magnetic layer is provided on a hard non-magnetic substrate such as P / Al. However, hard non-magnetic substrates such as glass and Ni-P / Al are relatively expensive, and about 30 to 40% of the disk cost is occupied by the above-mentioned hard non-magnetic substrates. Recently, with the rapid spread of portable personal computers such as notebook computers, there is a strong demand for further increase in the recording capacity of hard disks and reduction in costs.

Under these circumstances, conventional glass and Ni-
Attempts have been made to use a plastic nonmagnetic substrate obtained by injection molding a polymer such as polycarbonate or norbornene-based amorphous polyolefin instead of a hard nonmagnetic substrate such as P / Al. This type of disc has the advantage that the cost of the substrate can be less than 10% of the total cost of the disc, and the cost of the disc can be greatly reduced.

On the other hand, a conventional hard disk is made of CoCr.
When sputtering a Ta-based magnetic material, glass or Ni-P /
A substrate such as Al is heated to 250 ° C. or more, thereby
o By segregating Cr-rich non-magnetism around crystal grains,
The magnetic interaction between crystal grains is cut off to reduce noise in a high recording density region. The Cr-rich non-magnetic segregated around the Co crystal grains also has the effect of increasing the corrosion resistance of the magnetic film itself.

However, a thin film type magnetic recording medium using a plastic non-magnetic substrate is inferior in heat resistance of the substrate,
It is not possible to adopt a method in which the substrate is heated at the time of film formation to improve the magnetic properties due to nonmagnetic Cr segregation. For this reason, the film is formed without heating the substrate. In this case, it is necessary to physically separate the Co crystal grains and cut off the magnetic interaction. Among the magnetic materials, the CoCrPt-based magnetic material has a large crystal magnetic anisotropy, can obtain a relatively large coercive force even when formed at a low temperature, and achieves a high recording density when a plastic non-magnetic substrate is used. It is an important magnetic material for

Further, the conventional hard disk is inferior in reliability in terms of durability and corrosion resistance, as compared with a coating type medium, since the magnetic layer responsible for magnetic recording is made of a Co alloy-based metal thin film. In order to improve the reliability, an appropriate protective film, particularly a carbon-based protective film, is provided on the metal thin film.
The design of such a protective film is as important as the research and development of magnetic materials. In recent years, in order to realize a higher recording density, the thickness of the protective film has been reduced to less than 30 nm, and the flying height of the magnetic head at the time of recording / reproducing has been designed to be about 50 nm. Troiborogy between the slider and the protective film has been an important research topic.

[0008]

As described above, Ni-P
Using an injection-molded plastic non-magnetic substrate instead of a hard non-magnetic substrate such as Al or glass can greatly reduce the cost of a disk, but because the substrate has poor heat resistance, it can be used in a high recording density region. In order to reduce the noise, it is impossible to form a film while the substrate is heated. As a result, it is necessary to physically separate Co crystal grains and cut off magnetic interaction in order to reduce the noise. In order to obtain satisfactory magnetic characteristics by low-temperature film formation, it is desirable to use a CoCrPt-based magnetic material having large crystal magnetic anisotropy.

Here, as an effective means for physically separating Co crystal grains, an appropriate underlayer such as a non-magnetic Cr alloy is provided on a plastic non-magnetic substrate to roughen the surface of the substrate. There is a method of forming an alloy thin film. According to this, noise in the high recording density area is reduced, and S / N
Although the ratio is improved, on the other hand, the continuity of the magnetic layer composed of the thin film is reduced and the film is sparse. As a result, the surface roughness of the magnetic layer increases, the coverage of the carbon-based protective film decreases, and the corrosion resistance tends to deteriorate.

When a CoCrPt-based magnetic material is used as a Co alloy-based magnetic material and is sputtered on a plastic non-magnetic substrate at a low temperature, the non-magnetic Cr rich layer is sufficiently segregated around the Co crystal grains. In addition, since Pt is a noble metal, there is a problem that the corrosion resistance of the magnetic layer made of the magnetic material is further reduced due to a large electrochemical potential difference with Co.

In view of such circumstances, the present invention relates to a thin-film magnetic recording medium in which a Co alloy-based magnetic layer is provided on a plastic non-magnetic substrate, wherein the corrosion resistance of the magnetic layer is improved. It is another object of the present invention to provide a thin-film magnetic recording medium having excellent durability in addition to the above-mentioned corrosion resistance.

[0012]

Means for Solving the Problems In forming a Co alloy-based magnetic layer on a plastic non-magnetic substrate at a low temperature, the present inventors have proposed to physically separate Co crystal grains in order to reduce noise in a high recording density region. However, the continuity of the film is lost, the magnetic particles become coarse, the surface roughness of the magnetic layer becomes large, and if carbon is sputtered on this, the sputtered carbon cluster has high directivity. Therefore, the coverage of the protective film is reduced due to the shadowing effect, and the coverage between the valleys between the magnetic particles is particularly poor. In this portion, the magnetic layer is covered with the atmosphere (water and oxygen or NOx, SOx, etc.). It was considered that corrosion progressed in a state of being exposed to corrosive gas, and the corrosion resistance was remarkably deteriorated.

[0013] In order to enhance the coverage of the carbon-based protective film, studies have been made. As a result, carbon is sputtered on the Co-based magnetic layer in the presence of hydrogen gas or hydrocarbon.
When hydrogen gas is used as a carrier gas and hydrocarbons are used as a monomer gas, the carbon layer is coated by the CVD method, and active hydrogen generated in the system etches the convex portions of the magnetic layer surface, flattening the magnetic layer surface. As a result, the shadowing action is reduced, and the directivity of the carbon is low in a system in which activated carbon is generated, and the directivity to the magnetic layer is improved. As a result, it was found that the coatability of the magnetic layer was improved. Further, the carbon-based protective film thus formed is made of hydrogen-containing amorphous carbon in which active hydrogen and carbon are bonded, and the above-mentioned good covering properties can greatly improve the corrosion resistance of the Co-based magnetic layer. It has been found that even when a CoCrPt-based magnetic material having a large crystal magnetic anisotropy that gives good magnetic properties even at a low temperature is used, its corrosion resistance can be improved to a high degree.

On the other hand, according to such a carbon-based protective film made of hydrogen-containing amorphous carbon, a lubricating layer usually provided on the carbon-based protective film in order to improve the running durability and the like of a disk. There is a tendency that the friction coefficient in the existing state, that is, in the lubricated state, tends to increase, which becomes remarkable in proportion to the hydrogen content in the hydrogen-containing amorphous carbon and causes the above-mentioned durability to deteriorate. There was found. In order to overcome this problem, further investigations were made. As a result, the hydrogen-containing amorphous carbon was used as a first protective film (lower layer) to form a hydrogen-free amorphous carbon and a hydrogen-containing amorphous sulfur. However, a second protective film (upper layer) made of hydrogen-containing amorphous carbon whose content is lower than that of the first protective film or nitrogen-containing amorphous carbon in which nitrogen is added thereto is provided. By using a two-layer carbon-based protective film,
In addition to good corrosion resistance based on the first protective film, the second protective film reduced the coefficient of friction in a lubricated state, and found that very good results were obtained in the running durability of the disk. The invention has been completed.

That is, the present invention provides a magnetic recording medium comprising a Co alloy magnetic layer provided on a plastic non-magnetic substrate, a carbon protective film provided thereon, and a lubricating layer provided thereon. The carbon-based protective film is a first protective film (lower layer) made of hydrogen-containing amorphous carbon.
And a hydrogen-free amorphous carbon having a lower hydrogen content than the first protective film.
And a second protective film (upper layer) made of nitrogen or nitrogen-containing amorphous carbon containing nitrogen therein.
It is related to. Further, the hydrogen content of the hydrogen-containing amorphous carbon constituting the first protective film [H / (C
+ H)] is 0.2 to 0.5 (claim 2), and the hydrogen content [H / (C + H)] of the hydrogen-containing amorphous carbon constituting the second protective film is less than 0.2. (Claim 3), wherein the nitrogen content [N / (C + H + N)] of the nitrogen-containing amorphous carbon constituting the second protective film is 0.05 to 0.5 (claim 4). The present invention relates to the above magnetic recording medium.

According to the present invention, in these magnetic recording media, in particular, the total thickness of the first protective film and the second protective film in the carbon-based protective film is set to 30 nm or less. In the structure (Claim 5), the first thickness of the first protection film and the second protection film in the carbon-based protection film,
Wherein the proportion of the protective film is 20 to 75% (claim 6), wherein the plastic non-magnetic substrate is made of polycarbonate;
Norbornene-based amorphous polyolefin, polyether
A structure in which a polymer selected from terimide, polyethersulfone, and phenolic resin is injection-molded (claim 7), and a Co alloy-based magnetic layer is provided under a non-heated state of the plastic nonmagnetic substrate. A nonmagnetic inorganic buffer layer, a nonmagnetic Cr alloy underlayer or a nonmagnetic Ni-layer, between the plastic nonmagnetic substrate and the Co alloy magnetic layer.
A configuration in which a P underlayer is provided in this order (claim 9)
Each is a preferred embodiment.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As the plastic non-magnetic substrate in the present invention, polycarbonate, norbornene-based amorphous polyolefin, polyetherimide are used in place of rigid non-magnetic substrates such as Ni-P / Al and glass. What is obtained by injection-molding a polymer selected from polyethersulfone and phenol resin is used.
The thickness is not particularly limited, but is usually 0.5 to 2 mm.

In the present invention, when providing a Co alloy-based magnetic layer on the above-mentioned plastic non-magnetic substrate, as a base treatment, usually a non-magnetic inorganic buffer layer, a non-magnetic Cr alloy base layer or a non-magnetic Ni-base layer are used. A P underlayer is provided in this order. The former nonmagnetic inorganic buffer layer is used to increase the surface hardness of the substrate by providing this layer because the substrate is made of plastic and soft.
Normal thickness of iN, carbon, silicon etc. is 5-100
nm layers are used.

The latter nonmagnetic Cr alloy underlayer or nonmagnetic NiP underlayer makes the crystallite size of the Co alloy magnetic layer uniform and fine, and the c axis, which is the anisotropic principal axis of Co, is formed in the film plane. It has the role of orienting, and in particular, physically separates Co crystal grains to reduce noise in a high recording density region and thereby reduce S /
This contributes to the improvement of the N ratio. The thickness of the underlayer is usually preferably 5 to 100 nm. In addition, CrTi, CrV, CrM,
An alloy such as o is used.

The Co alloy-based magnetic layer in the present invention is provided on the above-mentioned plastic non-magnetic substrate via the above-mentioned undercoating layer. At this time, since the plastic non-magnetic substrate has poor heat resistance, low-temperature film formation in which the film is formed without heating the substrate, that is, without heating the substrate, is employed. Even if such low-temperature film formation is adopted,
By forming the underlayer, Co crystal grains can be sufficiently separated physically. The thickness of the Co alloy-based magnetic layer formed in this manner is not particularly limited, but is usually 1
The thickness is preferably 0 to 50 nm.

Here, as the Co alloy-based magnetic material, a conventional CoCrTa-based magnetic material can be used.
It is particularly preferable to use a CoCrPt-based magnetic material which has a large crystal magnetic anisotropy, can obtain a relatively large coercive force even when the film is formed at a low temperature, and is useful for realizing a high recording density. As this CoCrPt-based magnetic material, CoC
rPt, CoCrPtTa, CoCrPtTi, CoC
rPtTiTa, CoCrPtNi, CoCrPt-S
iO ₂ , CoCrPt-SiCx, CoCrPt-C,
CoCrPt-O and the like.

In the present invention, a first protective layer made of hydrogen-containing amorphous carbon is formed as a lower layer of a two-layer carbon-based protective film on the Co alloy-based magnetic layer formed at a low temperature in this manner. The provision of the film improves the corrosion resistance of the magnetic layer. This first protective film is formed by a method of sputtering carbon on a Co-based magnetic layer in an atmosphere of argon gas and hydrogen gas, argon gas and CH ₄ , C ₂ H ₆ ,
A method of sputtering carbon in a hydrocarbon atmosphere such as C ₂ H ₄ , using hydrogen gas as a carrier gas, CH ₄ ,
It is provided by a method of coating carbon by a CVD method using a hydrocarbon such as C ₂ H ₆ , C ₂ H ₄ , C ₆ H ₆ as a monomer gas.

In the method, active hydrogen generated in the plasma has an effect of etching the surface of the Co-based magnetic layer,
The protrusions on the surface of the magnetic layer generated when the Co crystal grains are physically separated are etched to reduce the surface roughness. In other words, the surface of the magnetic layer is flattened in the sputter,
Ing effect is reduced, and the coverage of the carbon-based protective film is enhanced. In the method of the above, hydrocarbons are decomposed in the plasma to generate active hydrogen and active carbon, and the active hydrogen flattens the surface of the Co-based magnetic layer by the same etching action as described above to reduce the shadowing action, Activated carbon, in addition to sputtered carbon clusters, serves as a source of carbon-based protective films, which have a particularly low directivity and a high throwing power to the magnetic layer surface. Therefore, the coverage of the carbon-based protective film is further improved. In the method (1), in addition to the same effect as described above, the coverage of the protective film is further enhanced by the low directivity unique to the CVD method.

In any of the above methods, the first protective film formed as described above becomes a hydrogen-containing amorphous carbon in which active hydrogen and active carbon are bonded. The hydrogen content of this hydrogen-containing amorphous carbon [H /
(C + H)] may be set to 0.2 to 0.5, preferably 0.3 to 0.4 by adjusting the amount of hydrogen gas or hydrocarbon introduced. If the hydrogen content is too low, the active hydrogen generated in the plasma is insufficient, and the effect of etching the surface projections of the Co-based magnetic layer is insufficient, so that the surface of the magnetic layer cannot be sufficiently flattened. Since the amount of activated carbon is low, a carbon source having low directivity is insufficient, and the coverage of the protective film is reduced. If the hydrogen content is excessive, the carbon-based protective film formed becomes polymer-like,
The film strength, especially the surface hardness, decreases, and the sliding resistance deteriorates.

The above-mentioned hydrogen-containing amorphous carbon may contain nitrogen in addition to carbon and hydrogen. The effect of increasing the film strength, in particular, the surface hardness, is obtained by incorporating nitrogen. At this time, the nitrogen content [N / (C + H + N)] is preferably 0.05 to 0.5, and more preferably 0.1 to 0.4. If the nitrogen content is too low or too high, good results cannot be obtained in improving the film strength. In order to contain nitrogen, a predetermined amount of nitrogen gas may be introduced into the system together with hydrogen gas, hydrocarbon, or the like in the above film formation methods.

In the present invention, the first protective film made of the above-mentioned hydrogen-containing amorphous carbon is used as a lower layer, and further, a hydrogen-free amorphous carbon is further provided thereon.
A two-layer structure is provided by providing, as an upper layer, a hydrogen-containing amorphous carbon having a lower hydrogen content than the first protective film or a second protective film made of nitrogen-containing amorphous carbon in which nitrogen is contained. Carbon protective film. With this configuration, in addition to the improvement of the corrosion resistance based on the lower layer, a favorable result can be obtained in maintaining the running durability and the like by reducing the friction coefficient in a lubricated state based on the upper layer.

Here, hydrogen-free amorphous masks
The carbon can be provided by a usual method of spattering carbon in an argon gas atmosphere. Further, the hydrogen-containing amorphous mask having a lower hydrogen content than the first protective film.
The hydrogen can be provided in accordance with the method for forming the first protective film. At this time, the introduction amount of hydrogen gas or hydrocarbon is reduced, and the hydrogen content in the amorphous carbon [H / (C
+ H)] is less than 0.2. Further, the nitrogen-containing amorphous carbon is formed in the system in the above-described method for forming a hydrogen-free amorphous carbon or a hydrogen-containing amorphous carbon having a lower hydrogen content than the first protective film. It can be provided by introducing a fixed amount of nitrogen gas. At this time, the nitrogen content [N / (C + H + N)] in the amorphous carbon is adjusted to be 0.05 to 0.5, preferably 0.1 to 0.4 for the same reason as described above. Is good.

The carbon protective film composed of the first protective film and the second protective film has a total film thickness of usually 30 n.
m or less. When the thickness is more than 30 nm, the magnetic spacing increases, which becomes an obstacle when recording and reproducing at a high density. The first and second protective films each preferably have a thickness of 5 nm or more. If the thickness is less than 5 nm, the first and second protective films do not become a continuous film, but grow in an island shape, thereby deteriorating the coverage and durability. Further, the ratio of the first protective film to the total thickness of the first protective film and the second protective film is preferably 20 to 75%. If it is less than 20%, the corrosion resistance will not be improved due to a decrease in coverage, and if it exceeds 75%, the durability will be reduced.

In the present invention, a lubricating layer is further provided on the carbon-based protective film to improve the durability of the magnetic recording medium. The thickness of the lubricating layer is usually 1 to 10 nm.
It is good to do. As the kind of the lubricant, “Fomblin-Z-AM2001” and “Dom-D” manufactured by Audimoto
OL, "-DEAL", "-DIAC", "Demunum-SA" manufactured by Daikin Industries, Ltd., "-S
H, "-SP", "-SY", "Krytox" manufactured by DuPont, and the like, perfluoropolyether-based lubricants, aliphatic hydrocarbon-based lubricants, and fluorine-substituted alkyl-based lubricants And a phosphoric ester-based lubricant. Among them, an appropriate one can be used according to the purpose of use.

[0030]

Next, an embodiment of the present invention will be described in more detail. Hereinafter, the hydrogen content [H / (C) in the first and second protective films constituting the carbon-based protective film will be described.
+ H)] is HFS (Hydrogen Forward)
Scattering) and the nitrogen content [N
/ (C + H + N)] is XPS (X-Ray Photo
(Spectroscopy).

Example 1 A norbornene-based amorphous polyolefin resin was injection-molded to produce a 3.5-inch plastic nonmagnetic substrate having a thickness of 1.2 mm. A 50 nm thick SiNx film was formed on this non-magnetic plastic substrate by DC magnetron sputtering in an argon gas atmosphere.
Non-magnetic inorganic buffer layer of NiPx having a thickness of 5
A non-magnetic Ni-P underlayer having a thickness of 0 nm and a Co alloy-based magnetic layer having a thickness of 15 nm made of a CoCrPt magnetic material were formed in this order.

On this magnetic layer, an argon gas flow rate of 90 s
A carbon protective target was DC-sputtered in an atmosphere of ccm and a CH ₄ gas flow rate of 40 sccm to form a first protective film having a thickness of 10 nm made of hydrogen-containing amorphous carbon. The hydrogen content in this first protective film [H /
(C + H)] was 0.29. Next, on this,
In an atmosphere of an argon gas flow rate of 90 sccm, a carbon target is DC-sputtered to form a second protective film having a thickness of 10 nm made of hydrogen-free amorphous carbon and having a total thickness of 20 nm. The carbon-based protective film having a two-layer structure was formed. Finally, on this carbon-based protective film,
A lubricant composed of stearylamine and a partially fluorinated alkyl ester was spin-coated to form a lubricating layer, thereby producing a magnetic recording medium having a sectional structure shown in FIG.

In the magnetic recording medium shown in FIG.
1 is a non-magnetic plastic substrate made of norbornene-based amorphous polyolefin resin, 2 is a non-magnetic inorganic buffer layer made of SiNx, 3 is a non-magnetic Ni-P underlayer made of NiPx, and 4 is Co made of CoCrPt magnetic material.
The alloy-based magnetic layer 5 has a two-layer carbon-based protective film comprising a first protective film 5A made of hydrogen-containing amorphous carbon and a second protective film 5B made of hydrogen-free amorphous carbon. Reference numeral 6 denotes a lubricating layer comprising stearylamine and a partially fluorinated alkyl ester.

Example 2 In forming a carbon-based protective film having a two-layer structure, an argon gas flow rate of 90 sccm and CH ₄ were formed after the formation of the first protective film.
In a gas flow rate of 10 sccm, the carbon target is subjected to DC sputtering to obtain a hydrogen content [H / (C + H)].
A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film having a thickness of 10 nm and made of hydrogen-containing amorphous carbon having a thickness of 0.08 was formed.

Example 3 In forming a carbon-based protective film having a two-layer structure, an argon gas flow rate of 90 sccm and CH ₄ were formed after the first protective film was formed.
In a gas flow rate of 20 sccm, the carbon target is subjected to DC sputtering to obtain a hydrogen content [H / (C + H)].
A magnetic recording medium was produced in the same manner as in Example 1 except that a second protective film having a thickness of 10 nm and comprising hydrogen-containing amorphous carbon having a thickness of 0.15 was formed.

Example 4 In forming a carbon-based protective film having a two-layer structure, after forming the first protective film, a carbon target was formed in an atmosphere of an argon gas flow rate of 90 sccm and a nitrogen gas flow rate of 30 sccm. DC spatter to remove nitrogen content [N / (C + H +
N)] A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film having a thickness of 10 nm made of nitrogen-containing amorphous carbon with (H = 0) of 0.07 was formed. did.

Example 5 In forming a carbon-based protective film having a two-layer structure, after forming the first protective film, a carbon target was formed in an atmosphere of an argon gas flow rate of 90 sccm and a nitrogen gas flow rate of 60 sccm. DC spatter to remove nitrogen content [N / (C + H +
N)] (H = 0) A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film having a thickness of 10 nm and comprising nitrogen-containing amorphous carbon having a thickness of 0.14 was formed. did.

Example 6 In forming a carbon-based protective film having a two-layer structure, after forming the first protective film, a carbon target was formed in an atmosphere of an argon gas flow rate of 90 sccm and a nitrogen gas flow rate of 90 sccm. DC spatter to remove nitrogen content [N / (C + H +
N)] (H = 0) A magnetic recording medium was manufactured in the same manner as in Example 1, except that a second protective film having a thickness of 10 nm and comprising nitrogen-containing amorphous carbon having a thickness of 0.28 was formed. did.

Example 7 In forming a carbon-based protective film having a two-layer structure, a carbon sputter was applied on a Co alloy-based magnetic layer in an atmosphere of an argon gas flow rate of 90 sccm and a hydrogen gas flow rate of 20 sccm by a DC sputtering method. Then, a first protective film made of hydrogen-containing amorphous carbon and having a thickness of 10 nm was formed. The hydrogen content [H / (C + H)] in the first protective film is 0.2
I got 2. A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film similar to that of Example 1 was formed thereon.

Example 8 In forming a carbon-based protective film having a two-layer structure, a carbon protective film was formed on a Co alloy-based magnetic layer in an atmosphere of an argon gas flow rate of 90 sccm, a hydrogen gas flow rate of 60 sccm, and a nitrogen gas flow rate of 40 sccm. -DC spatter on the target to obtain a hydrogen and nitrogen containing amorphous carbon
A first protective film having a thickness of nm was formed. The hydrogen content [H / (C + H)] in the first protective film was 0.41, and the nitrogen content [N / (C + H + N)] was 0.11. A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film similar to that in Example 2 was formed thereon.

Example 9 In forming a carbon-based protective film having a two-layer structure, a carbon target was placed on a Co alloy-based magnetic layer in an atmosphere of an argon gas flow rate of 90 sccm and a CH ₄ gas flow rate of 20 sccm using a DC target. As a sputter, a first protective film made of hydrogen-containing amorphous carbon and having a thickness of 10 nm was formed. The hydrogen content [H / (C + H)] in the first protective film is 0.1.
It was 21. A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film similar to that of Example 3 was formed thereon.

Example 10 In forming a carbon-based protective film having a two-layer structure, a carbon-based protective layer was formed on a Co alloy-based magnetic layer in an atmosphere of an argon gas flow rate of 90 sccm, a CH ₄ gas flow rate of 60 sccm, and a nitrogen gas flow rate of 40 sccm. The bonder is DC-sputtered to form a hydrogen and nitrogen containing amorphous carbon having a thickness of 1%.
A first protective film having a thickness of 0 nm was formed. The hydrogen content [H / (C + H)] in the first protective film was 0.40, and the nitrogen content [N / (C + H + N)] was 0.11. A magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film similar to that in Example 4 was formed thereon.

Embodiment 11 In forming a carbon protective film having a two-layer structure, a 13.56 MHz high frequency power supply was applied on a Co alloy magnetic layer in an atmosphere of a hydrogen gas flow rate of 40 sccm and a CH ₄ gas flow rate of 100 sccm. A first protective film made of hydrogen-containing amorphous carbon and having a thickness of 10 nm was formed by the used CVD method. The hydrogen content in this first protective film [H
/ (C + H)] was 0.37. Then, this first
A magnetic recording medium was manufactured in the same manner as in Example 1, except that a second protective film similar to that of Example 5 was formed on the protective film of Example 5.

Example 12 In forming a carbon-based protective film having a two-layer structure, 13. a hydrogen gas flow rate of 80 sccm, a CH ₄ gas flow rate of 100 sccm, and a nitrogen gas flow rate of 40 sccm were formed on the Co alloy magnetic layer. A film was formed by a CVD method using a high frequency power supply of 56 MHz, and a first protective film made of hydrogen and nitrogen-containing amorphous carbon and having a thickness of 10 nm was formed.
The hydrogen content [H / (C + H)] in the first protective film is 0.48, and the nitrogen content [N / (C + H + N)] is 0.1.
It was 0. Then, a magnetic recording medium was manufactured in the same manner as in Example 1 except that a second protective film similar to that of Example 6 was formed on the first protective film.

Comparative Example 1 An argon gas flow rate of 90 sccm was formed on a Co alloy magnetic layer.
Except that the carbon target was DC-sputtered in the atmosphere described above to form a single-layered carbon-based protective film having a thickness of 20 nm made of hydrogen-free amorphous carbon. A magnetic recording medium was manufactured in the same manner as in Example 1.

Comparative Example 2 An argon gas flow rate of 90 scc was formed on the Co alloy magnetic layer.
m and a nitrogen gas flow rate of 30 sccm, the carbon target was subjected to DC sputtering to obtain a nitrogen content [N / (C
+ H + N)] (H = 0) is a single-layered car having a thickness of 20 nm and made of nitrogen-containing amorphous carbon having a thickness of 0.19.
A magnetic recording medium was manufactured in the same manner as in Example 1 except that a carbon-based protective film was formed.

Comparative Example 3 An argon gas flow rate of 90 scc was formed on a Co alloy magnetic layer.
m, in a 10 sccm atmosphere of CH ₄ gas, the carbon target was subjected to DC sputtering to obtain a hydrogen content [H / (C +
H)] A magnetic recording medium was produced in the same manner as in Example 1 except that a single-layered carbon-based protective film having a thickness of 20 nm made of hydrogen-containing amorphous carbon having a thickness of 0.08 was formed. did.

Comparative Example 4 An argon gas flow rate of 90 scc was formed on the Co alloy magnetic layer.
m, the carbon target was subjected to DC sputtering in an atmosphere of CH ₄ gas 40 sccm, and the hydrogen content [H / (C +
H)] A magnetic recording medium was produced in the same manner as in Example 1 except that a single-layered carbon-based protective film having a thickness of 20 nm made of hydrogen-containing amorphous carbon having a thickness of 0.29 was formed. did.

The above Examples 1 to 12 and Comparative Examples 1 to 4
For each of the magnetic recording media described above, the Co concentration on the medium surface before providing the lubricating layer was determined by XPS (X-Ray Photo Sp).
(Ectroscopy). After the lubrication layer is provided, the CSS (Contac) is obtained by the following method.
t Start and Stop) A durability test was performed to evaluate durability. These results are summarized in Table 1. Further, it was left in an environment of 60 ° C. and 90% RH, and the change in the saturation magnetization of the magnetic layer was examined to evaluate the corrosion resistance. The results are shown in Table 2.

<CSS Durability Test> DLC (Diamo
An Al ₂ O ₃ / TiC slider coated with a 10 nm thickness (nd Like Carbon) was used with a vertical load of 3.5 g. The test method is to accelerate to a linear velocity of 12.5 m / sec in 3 seconds, hold at 12.5 m / sec for 10 seconds, decelerate in 6 seconds, and stop for 11 seconds.
This is a test of 0 seconds, and the number of cycles until the carbon protective film and the Co alloy magnetic layer are broken through the lubricating layer is determined by this test.

[0051]

[0052]

From the above Tables 1 and 2, the two-layered structure of the first protective film composed of hydrogen-containing amorphous carbon and the second protective film composed of hydrogen-free amorphous carbon and the like is shown. In all of the magnetic recording media of Examples 1 to 12 provided with a carbon-based protective film, Co was not detected at all from the medium surface due to the high covering property based on the first protective film. , 90% RH,
The reduction rate of the saturation magnetization of the magnetic layer is small, high corrosion resistance is obtained, and in addition to this good corrosion resistance,
The protective film reduces the coefficient of friction in a lubricated state,
It is also clear that very good results have been obtained in the S endurance test.

On the other hand, of the magnetic recording media of Comparative Examples 1 to 4 provided with a carbon-based protective film having a single-layer structure, the protective film was made of pure amorphous carbon not containing hydrogen. In Example 1, Comparative Example 2 composed of nitrogen-containing amorphous carbon, and Comparative Example 3 composed of hydrogen-containing amorphous carbon containing hydrogen but having a low hydrogen content, the covering properties of the protective film were all low. Low, Co
Are 1.7 atomic%, 1.3 atomic%, and 0.5 atomic%, respectively.
Therefore, when left in an environment of 60 ° C. and 90% RH, the saturation magnetization of the magnetic layer is greatly reduced in accordance with the amount of precipitation. Comparative Example 4 composed of hydrogen-containing amorphous carbon having a high hydrogen content
Does not detect Co on the medium surface, but the coefficient of friction in a lubricated state is reduced, and good results cannot be obtained in a CSS durability test.

Example 13 In forming a carbon-based protective film having a two-layer structure, a carbon target was deposited on a Co alloy-based magnetic layer in an atmosphere having an argon flow rate of 90 sccm and a CH ₄ gas flow rate of 40 sccm.
C spatter to reduce the hydrogen content [H / (C + H)] to 0.
29 hydrogen-containing amorphous carbons having a thickness of A
A first protective film having a thickness of 10 nm is formed on the first protective film, and a carbon target is subjected to DC sputtering in an atmosphere of an argon gas flow rate of 90 sccm and a nitrogen gas flow rate of 30 sccm to obtain a nitrogen content [N / (C + H + N)]. A second protective film made of nitrogen-containing amorphous carbon (H = 0) of 0.07 and having a thickness of B nm is formed, and the total film thickness of the first and second protective films (A + B) is formed. ) Was 25 nm, except that the thicknesses of A and B were as shown in Table 3 in the same manner as in Example 1. Magnetic recording media 1 to 6 were produced.

For each of the magnetic recording media, a decrease in saturation magnetization after being left for 4 weeks in an environment of 60 ° C. and 90% RH was measured as a corrosion resistance test in the same manner as described above. I went. The results are shown in Table 3 below. From the results in Table 3, the ratio [A / (A + B)] × 100 (%) occupied by the first protective film in the total film thickness of the first protective film and the second protective film is 20 to 75. %
No. in the range of No. The magnetic recording media of Nos. 2 to 5 highly satisfy both the characteristics of corrosion resistance and CSS durability, and it is understood that it is desirable to set them within the above ranges.

[0057]

[0058]

According to the present invention, a Co alloy-based magnetic layer is formed on a plastic non-magnetic substrate by low-temperature deposition, and a first protective film made of hydrogen-containing amorphous carbon and a hydrogen-free amorphous film are formed thereon. Providing a carbon-based protective film having a two-layer structure with a second protective film made of carbon or the like;
In addition, by providing a lubrication layer on it,
The magnetic recording medium having excellent corrosion resistance can be provided by the high covering property based on the first protective film, and the second recording medium can be provided.
Based on the protective film described above, there is an effect that a magnetic recording medium having excellent running durability and the like can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a magnetic recording medium of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 plastic non-magnetic substrate 2 non-magnetic inorganic buffer layer 3 non-magnetic Ni-P underlayer 4 Co alloy magnetic layer 5 carbon-based protective film 5A first protective film (lower layer) 5B second protective film (upper layer) 6) Lubrication layer

Continued on the front page (72) Inventor Takashi Sekiguchi 1-88 Ushitora 1-chome, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (9)

[Claims] 1. A magnetic recording medium comprising: a Co alloy-based magnetic layer provided on a plastic non-magnetic substrate; a carbon-based protective film provided thereon; and a lubricating layer provided thereon.
The above carbon-based protective film is made of hydrogen-containing amorphous mask.
A first protective film (lower layer) made of carbon, a non-hydrogen-containing amorphous carbon, a hydrogen-containing amorphous carbon having a lower hydrogen content than that of the first protective film, or nitrogen containing nitrogen. A magnetic recording medium comprising: a second protective film (upper layer) made of amorphous carbon. 2. The carbon-based protective film, wherein the hydrogen content [H / (C + H)] of the hydrogen-containing amorphous carbon constituting the first protective film is 0.2 to 0.5. 1
3. The magnetic recording medium according to claim 1. 3. The carbon protective film according to claim 1, wherein the hydrogen content [H / (C + H)] of the hydrogen-containing amorphous carbon constituting the second protective film is less than 0.2. 3. The magnetic recording medium according to claim 1. 4. The carbon-based protective film, wherein the nitrogen-containing amorphous carbon constituting the second protective film has a nitrogen content [N / (C + H + N)] of 0.05 to 0.5. 3. The magnetic recording medium according to 1 or 2. 5. The magnetic material according to claim 1, wherein in the carbon-based protective film, the total thickness of the first protective film and the second protective film is set to 30 nm or less. recoding media. 6. The carbon-based protective film, wherein the proportion of the first protective film in the total film thickness of the first protective film and the second protective film is 20 to 75%. 6. The magnetic recording medium according to any one of items 1 to 5, 7. The plastic non-magnetic substrate includes polycarbonate, norbornene-based amorphous polyolefin,
7. The magnetic recording medium according to claim 1, wherein a polymer selected from polyetherimide, polyethersulfon, and phenol resin is injection-molded. 8. The magnetic recording medium according to claim 1, wherein the Co alloy-based magnetic layer is made of a CoCrPt-based magnetic material provided on a non-heated plastic non-magnetic substrate. 9. A non-magnetic inorganic buffer layer and a non-magnetic Cr layer between a plastic non-magnetic substrate and a Co alloy-based magnetic layer.
9. The magnetic recording medium according to claim 1, wherein an alloy underlayer or a non-magnetic Ni-P underlayer is provided in this order.