JPH1166531A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a coercive force and to achieve a high surface recording density by a method wherein an alloy magnetic layer in a magnetic recording medium in which a substrate layer and the alloy magnetic layer are provided on a nonmagnetic substrate is formed in such a way that carbon at specific atomic % or higher is contained over the whole region in its thickness direction. SOLUTION: A nonmagnetic substrate in which an NiP plating treatment is executed to its surface and whose surface is polished is set inside a sputtering apparatus whose vacuum is evacuated in advance down to 5×10<6> Pa, and it is heated at about 250 deg.C. Then, a gas in the ratio of 14 of H2 to 86 of high- purity Cr is introduced into a pure Cr substrate layer, a Co-based magnetic layer and a hydrogenated carbon protective layer in this sequence, and the respective layers are formed continuously. In this case, a substrate temperature is kept at 200 deg.C or higher, the film thickness of the Cr substrate layer is set at 300 Å, that of the Co-based magnetic layer is set at 200 Å, and that of the hydrogenated carbon protective layer is set at 150 Å. At this point, carbon becomes 0.5 atomic % or higher over the whole region in the thickness direction of the Co-based magnetic layer. Thereby, a coercive force can be enhanced, and a high surface recording density can be achieved.

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 used for a magnetic disk drive and the like.

[0002]

2. Description of the Related Art A magnetic disk medium is generally formed by a sputtering method on a non-magnetic substrate such as a substrate made of an Al--Mg alloy plated with NiP electroless plating. At this time, the substrate surface is often subjected to polishing and texturing before use. The medium configuration is a base film mainly composed of Cr, a Co-based alloy magnetic film,
It is general that a protective layer mainly composed of carbon or the like is formed in this order.

Since the magnetostatic characteristics of a magnetic disk medium vary depending on the type of magnetic film material, film forming conditions for forming the medium, the configuration of the underlayer, etc., the conditions must be optimized to achieve the target static magnetic characteristics. We do and correspond. However, in recent years,
The areal recording density of magnetic disks is increasing at a rapid pace reaching 60% per year, and magnetic disk media is required to have strict characteristics accordingly. In particular, at present, the magnetostatic properties of the magnetic film of the medium, especially the coercive force, are required to be higher as the areal recording density increases. Therefore, forming a magnetic thin film layer having a high coercive force has always been a major issue in the development of magnetic disk media.

In order to solve such a problem, the magnetic layer material has been changed so far. Particularly widely used is a method of adding Pt to a Co-based magnetic material to generate a high coercive force, but this method is not industrially preferable because it uses extremely expensive Pt. . There is also a disadvantage that noise increases.

[0005]

As described above, the surface recording density of a magnetic disk medium is increasing at a rapid pace, and the value of the coercive force required for the medium is constantly increasing. To respond to this, we are changing the material of the magnetic layer and changing the film formation conditions, but it is difficult to search for a new material, and there is a limit to the improvement within the material. Is becoming more difficult.

[0006]

SUMMARY OF THE INVENTION A magnetic disk medium is usually provided with a protective layer in the form of a magnetic layer in order to protect the magnetic layer from corrosion and damage. Typical materials for the protective layer include carbon-based materials such as carbon, hydrogenated carbon, and carbon nitride, and materials such as silicon oxide and zirconium oxide. These protective layers are selected and set with an emphasis on the performance for improving the durability of the magnetic disk, and attention has not been paid to the correlation with the magnetic properties of the medium.

In a process of examining various phenomena between a magnetic layer and a protective layer in a magnetic disk medium, the inventors have studied a magnetic disk medium in which carbon or a compound containing carbon as a main component is used as a material for a protective layer. At
Those satisfying specific conditions have been found to have a particularly high coercive force, and have reached the present invention.

That is, the gist of the present invention is that in a magnetic recording medium having at least an underlayer and an alloy magnetic layer on a nonmagnetic substrate, the alloy magnetic layer has a thickness of 0.5
Present in magnetic recording media containing at least atomic% of carbon.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the magnetic recording medium according to the present invention, several methods such as Auger electron spectroscopy and secondary ion mass spectrometry are widely used for measuring the carbon concentration in the magnetic layer, but the analysis method is scientifically reliable. I just need. At least, when the concentration is measured using either the Auger electron spectroscopy or the secondary ion mass spectrometry, at least one of the analysis results indicates that 0.5 atomic atoms of carbon are present in the entire thickness direction of the magnetic layer. %, The effect of the present invention can be expected in all magnetic recording media that can obtain the result of being present in an amount of not less than%.

Here, the entire region in the thickness direction of the magnetic layer means the entire region from the uppermost portion to the lowermost portion defined by the following rules. (Top) (1) When the layer containing carbon is on the magnetic layer The element is digged from the outermost surface of the carbon-based protective layer by the argon ion etching method using an analysis method such as Auger electron spectroscopy (AES). It indicates the depth at which the concentration of carbon becomes the same as the concentration of Co when the analysis is performed. (2) In the case where the layer containing carbon is not on the magnetic layer This indicates the surface of the magnetic layer.

(Lower) The depth at which the concentration of Co becomes the same as the concentration of the main element in the metal underlayer when elemental analysis is performed while digging by argon ion etching. For example, when the metal underlayer is a pure Cr layer, the depth is such that the Co concentration and the Cr concentration are the same.

[0012] The magnetic recording medium of the present invention is characterized in that the entire region from the uppermost portion to the lowermost portion in the thickness direction of the magnetic layer contains 0.5% or more of carbon atoms. Preferably, the content is 0.5% or more in the entire region and 3% or less in the lowermost portion of the magnetic layer. When carbon atoms are not contained in the entire region in the thickness direction of the magnetic layer, or when the content is less than 0.5%, the effect of improving coercive force cannot be obtained.

In the present invention, carbon atoms may be contained in the magnetic layer by, for example, adding carbon to the material of the magnetic layer when the magnetic layer is provided, but a protective layer containing carbon may be provided on the magnetic layer. Alternatively, a method of diffusing carbon atoms in the protective layer may be used.

The non-magnetic substrate usable in the magnetic recording medium of the present invention includes a non-magnetic substrate such as an Al—Mg alloy substrate plated with NiP, a soda glass, an aluminosilicate glass, silicon, titanium, various ceramics, and carbon. Is optional. However, when the substrate is heated during the formation of the medium, it is needless to say that the substrate should be selected in accordance with the conditions so that the heat resistance corresponding thereto is required.

The surface of the substrate may be textured by mechanical processing for reducing the coefficient of friction or laser beam processing. The metal underlayer, the alloy magnetic layer, and the carbon-based protective layer may be any physical film forming method such as a direct current sputtering method, a high frequency sputtering method, an ion beam epitaxy, and a vacuum evaporation method. Generally, a direct current or high frequency sputtering method is often used. Further, a constant substrate bias voltage may be applied to the substrate during the film formation. This substrate bias is a DC bias,
Either high frequency bias can be used.

As the alloy magnetic layer that can be used in the magnetic recording medium of the present invention, a known ferromagnetic alloy material can be arbitrarily used, but a Co-based alloy magnetic layer is preferable from the viewpoint of high coercive force. Is there a special reason?). CoP alloy magnetic layers include CoP, CoCr, CoCrTa,
CoNiCr, CoCrPt, CoCrPtTa, Co
Includes all alloy materials containing Co as a main component, such as NiCrPt and CoCrPtB. The thicknesses of these magnetic layers are set in accordance with desired magnetic properties, as in the case of the metal underlayer. The thickness range is 500 ° or less, preferably 10
0 to 300 °, more preferably 150 to 250 °.

An underlayer constituting the magnetic recording medium of the present invention;
Each of the thin film layers such as the alloy magnetic layer may have a multilayer structure composed of two or more layers. Further, a liquid or solid lubricant may be applied on the protective layer containing carbon. The underlayer referred to here is a Cr film, which is widely used at present,
All the metal-based underlayers, including the -V alloy film, the Cr-Ti alloy film, the Cr oxide film, etc., are included. The element most present in the metal-based underlayer at the atomic concentration is referred to as the main component of the metal-based underlayer. The thickness of these underlayers is set in accordance with the desired medium performance, but a thickness of about several hundreds of mm is generally used.

As the protective layer containing carbon, any material can be used. However, it is preferable that carbon is a main component. Particularly, when carbon in the protective layer is diffused into the magnetic layer, carbon is mainly used. It is preferred to use a protective layer of the components. Specific examples of the material of the protective layer include a pure carbon film, a hydrogenated carbon film, a carbon nitride film, a hydrogenated carbon nitride film, and the like.

Here, the hydrogenated carbon film refers to a carbon-based thin film formed by a sputtering method using a carbon target, in addition to a rare gas such as ordinary argon as a sputtering gas, H ₂ , CH _4, or the like. The film was formed while introducing gas. Usually, the material used as the protective layer of the formed disk contains about 20 atomic% to 35 atomic% of hydrogen in the film. In the case of a specific film quality, it is widely used because it shows superior wear resistance as compared with general a-carbon. As the film forming method, either a DC sputtering method or a high frequency sputtering method is possible, and the film may be formed while applying a DC or high frequency bias voltage to the substrate.

A carbon nitride film is a carbon-based thin film formed by a sputtering method using a carbon target in the same manner as a hydrogenated carbon film. A gaseous CNx intermediate is formed by nitriding by the contained plasma, and is formed as a CNx film on a substrate. In addition to rare gases, N
2 is introduced into a vacuum chamber to form a film. The film formation method may be either a direct current sputtering method or a high frequency sputtering method. Further, these carbon-based protective films may be crystalline or amorphous. The thickness of the carbon-based protective layer is 50 to 5
00 °, preferably about 50 to 300 °, and more preferably about 50 to 150 °.

As described above, the magnetic recording medium of the present invention has a carbon atom content of 0.5 atomic% over the entire region in the thickness direction of the magnetic layer.
The method for obtaining the magnetic recording medium of the present invention includes, for example, 5 × 1
A high-purity argon gas is introduced into a container evacuated to 0 ^-6 Pa or less, and a metal underlayer is formed at 200 ° C to 300 ° C.
After forming the Co-based magnetic layer, a method of depositing a carbon-based protective layer while maintaining the substrate temperature at a high temperature of 200 ° C. or higher and without breaking the vacuum atmosphere, or 5 × 1
A rare gas such as a high-purity argon gas is introduced in a small amount into a container evacuated to 0 ^-5 Pa or less, and a sputtering method is used.
There is a method of forming a metal underlayer, a Co-based magnetic layer, and a carbon-based protective layer, and then performing a heat treatment at 200 ° C. or more in a vacuum atmosphere of 5 × 10 ⁻⁶ Pa or less. You may.

[0022]

The present invention will be described in more detail with reference to the following examples. (Example 1) A sputtering apparatus for manufacturing a magnetic disk was evacuated to 5 × 10 ⁻⁶ Pa in advance. NiP plating is applied to the surface and the average surface roughness Ra is 5Å
The surface polished as follows was set in the apparatus, and the substrate surface temperature was heated to about 250 ° C. using a lamp heater set in a vacuum chamber.

Then, immediately, a pure Cr underlayer, Co-1
Each layer of the medium is continuously formed using a DC sputtering method in the order of a 3Cr-4Ta (atomic%) magnetic layer and a protective layer of hydrogenated carbon (produced by introducing gas at a ratio of H ₂ 14 to high purity Ar86). Formed. At this time, the time interval between the completion of the formation of each layer and the formation of the next layer is set to be within 10 seconds so that the decrease in the substrate temperature due to natural cooling is suppressed as much as possible. The substrate temperature during the formation was set to 200 ° C. or higher. The thicknesses of the respective layers were a Cr underlayer 300 °, a Co-13Cr-4Ta (atomic%)-based magnetic layer 200 °, and hydrogenated carbon 150 °.
Among them, the ground is -2 with respect to the ground when the magnetic layer is formed.
A DC bias voltage of 00V was applied.

The magnetic disk medium thus manufactured was subjected to elemental analysis using Auger electron spectroscopy. Element analysis of the etched portion was performed while performing ion etching from the surface of the medium with an ion gun set at 3 kV-300 nA, scanning x100. As a result, an element distribution in the film thickness direction as shown in FIG. 1 was obtained. From this, it was found that carbon was detected over the entire region from the uppermost portion to the lowermost portion of the Co-based magnetic layer, and the concentration was about 1 atomic%.

On the other hand, a part of the magnetic disk medium was cut out, and the static magnetic characteristics were measured using a sample vibration magnetometer (VSM). The results were as shown in Table 1.

Comparative Example 1 A sputtering apparatus for manufacturing a magnetic disk was evacuated to 2 × 10 ⁻⁵ Pa in advance. The surface is subjected to NiP plating, and the surface is polished so that the average surface roughness Ra is 5 ° or less. The apparatus is set in an apparatus, and the substrate surface temperature is set to about 250 ° C. using a lamp heater set in a vacuum chamber. Heated. Thereafter, a pure Cr underlayer, Co-13Cr-4Ta (atomic%)
Magnetic layer, hydrogenated carbon (high purity Ar86 vs. H214
(Introduced gas at a rate of 2).

At this time, the thicknesses of the respective layers were a Cr underlayer 300 °, a Co-13Cr-4Ta (at.%)-Based magnetic layer 200 °, and hydrogenated carbon 150 °, respectively. During the formation of the magnetic layer, a DC bias voltage of -200 V was applied to the substrate with respect to the ground. In addition, a Cr underlayer and Co-
The film was quickly formed up to the 13Cr-4Ta-based magnetic layer, but the final formation of the hydrogenated C protective layer was performed at a substrate temperature of 100 ° C.
Went down.

The magnetic disk medium manufactured as described above was examined by Auger electron spectroscopy in the same manner as in Example 1. At this time, the element distribution in the film thickness direction was as shown in FIG. It can be seen from the graph that C is near the bottom of the Co-based magnetic layer.
Was 0.3%, and it was found that almost no Nb was present. Further, a part of the magnetic disk medium was cut out in the same manner as in Example 1, and a sample vibration magnetometer (VS.
M. ) Was used to measure the magnetostatic properties. The results are shown in Table 1 together with the results of Example 1.

(Comparative Example 2) The same sputtering apparatus as used for producing the magnetic disk medium of Example 1 was evacuated to 5 × 10 ⁻⁶ Pa in advance. The surface is subjected to NiP plating, and the surface is polished so that the average surface roughness Ra is 5 ° or less. The apparatus is set in an apparatus, and the substrate surface temperature is set to about 250 ° C. using a lamp heater set in a vacuum chamber. Heated. Immediately thereafter, each layer of the medium was continuously formed by using a direct current sputtering method in the order of a pure Cr underlayer and a Co-13Cr-4Ta (atomic%) magnetic layer.

At this time, the time interval between the completion of the formation of the Cr underlayer and the formation of the next Co-13Cr-4Ta (at.%) Magnetic layer is set to within 10 seconds, and the substrate temperature by natural cooling is reduced. Was suppressed as much as possible. No protective layer was formed. In addition, Co-13Cr-4
In order to prevent the Ta-based magnetic layer surface from being oxidized, the magnetic disk medium was left as it was in a high vacuum environment until the temperature of the medium dropped to room temperature. The thickness of each layer is C
r Underlayer 300%, Co-13Cr-4Ta (atomic%)
The system magnetic layer was 200 mm. During the formation of the magnetic layer, a DC bias voltage of -200 V was applied to the substrate with respect to the ground.

In the magnetic disk medium of Comparative Example 2, there is no possibility that carbon atoms diffuse into the magnetic film because no carbon-based protective layer is formed. The coercive force values at this time are shown in Table 1. The medium was manufactured under almost the same conditions as in Example 1 except that the hydrogenated C protective layer was not formed, but the coercive force was significantly lower than that of Example 1 as shown in Table 1. .

[0032]

[Table 1]

[0033]

As described above, according to the magnetic recording medium of the present invention, since the magnetic layer has the alloy magnetic layer containing a specific concentration of carbon, the coercive force can be improved, and This contributes to achieving the areal recording density.

[Brief description of the drawings]

FIG. 1 is a graph showing an analysis result of a magnetic recording medium obtained in Example 1.

FIG. 2 is a graph showing an analysis result of the magnetic recording medium obtained in Comparative Example 1.

Claims (4)

[Claims] 1. A magnetic recording medium having at least a base layer and an alloy magnetic layer on a nonmagnetic substrate, wherein the alloy magnetic layer contains 0.5 atomic% or more of carbon over the entire area in the thickness direction. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein a layer containing carbon is provided on the alloy magnetic layer. 3. The method according to claim 1, wherein the carbon atoms contained in the alloy magnetic layer are:
The magnetic recording medium according to claim 2, wherein the magnetic recording medium is diffused into the alloy magnetic layer when the carbon-containing layer is provided. 4. In a magnetic recording medium having at least a base layer, an alloy magnetic layer, and a carbon-containing layer provided on the alloy magnetic layer on a non-magnetic substrate, the carbon layer extends over the entire area in the thickness direction of the alloy magnetic layer. A magnetic recording medium containing 0.5 atomic% or more of atoms and having a higher concentration as it is closer to the layer containing carbon.