JPH05159290A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the process for production of the magnetic recording medium which has the higher coercive force than heretofore and can deal with the trend toward a higher recording density. CONSTITUTION:A magnetic material layer 3 consisting of a Co alloy, such as CoNiCr, is first formed on a carbon substrate 1 heated to a prescribed temp. by using a sputtering method while a bias voltage from -1000 to -300V is impressed to this substrate 1. A protective layer 4 consisting of carbon is then formed on this magnetic layer 3. The coercive force of the magnetic material layer is enhanced. Since the carbon substrate is light in weight, the load of a driving motor is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium such as a magnetic disk and a magnetic drum used in an external recording device such as a computer, and particularly to a magnetic recording suitable for manufacturing a magnetic recording medium having a high recording density. The present invention relates to a method of manufacturing a medium.

[0002]

2. Description of the Related Art In recent years, an increase in the amount of information has promoted an increase in the capacity and recording density of magnetic disks used in external recording devices of computers. The magnetization transition width a is one of the factors showing the performance of this kind of magnetic recording medium.
In order to increase the recording density of the magnetic recording medium, it is necessary to reduce the magnetization transition width a. This magnetization transition width a is
Assuming that the magnetic layer thickness is δ, the residual magnetic flux density is Br, the factor relating to the squareness is m, and the coercive force is Hc, these have the following relationships.

A∝δ ・ Br / (m ・ Hc)

That is, in order to increase the recording density of the magnetic recording medium, it is preferable that the value of the coercive force Hc is as large as possible.

By the way, at present, magnetic recording media are manufactured by the following method.

Coating Method A magnetic recording medium is prepared by mixing acicular γ-Fe ₂ O ₃ with Al ₂ O ₃ and a binder and applying the mixed solution onto an aluminum alloy substrate using a spin coating method. To manufacture. In this coating method, the magnetic material layer is thinned by improving the coating method of the mixed solution, and the γ-Fe ₂ O
₃ It has been studied to increase the coercive force of magnetic recording media by methods such as miniaturization of acicular particles and Co deposition.

Plating method Co is deposited on the NiP / Al substrate using the electroless plating method.
A magnetic recording medium is manufactured by forming a metal magnetic layer made of P or CoNiP or the like. In this method, the magnetic material layer can be made thinner and the coercive force can be made higher than that of the magnetic recording medium by the coating method. Further, it has been studied to further increase the coercive force of the magnetic recording medium by methods such as further thinning the magnetic layer and improving the plating bath composition.

Sputtering Method A metallic magnetic layer is formed on a NiP / Al substrate by using a sputtering apparatus. With this sputtering method, a higher coercive force than that of the plating method can be achieved.

As described above, various methods are currently being attempted to further increase the recording density of the magnetic recording medium. However, since the coating method and the plating method are not satisfactory in terms of productivity, operability and recording density, the sputtering method is becoming the mainstream.

In this sputtering method as well, various studies have been conducted in order to cope with a higher recording density. For example, in general, the magnetic layer is CoN
Thin films made of i, CoNiCr or CoCrTa have been used. Instead of the magnetic layer of these compositions, CoC
Attempts have been made to increase the coercive force by a magnetic layer having a composition using a noble metal such as rPt. It is also known that a magnetic layer having a high coercive force can be obtained by heating a substrate to a high temperature to form a magnetic layer (for example, Ishikawa et al., 11th Annual Meeting of the Japan Society for Applied Magnetics). Shu, 1-pA-10
, 1988). Furthermore, it is known that a magnetic layer having a high coercive force can be obtained by forming the magnetic layer while applying a negative bias voltage to the substrate (for example, Hashimoto et al.
Proceedings of the 35th Joint Lecture on Applied Physics, 29a-C-9,10,19
88 years).

[0011]

However, the conventional method for producing a magnetic recording medium using the sputtering method is
There are the following problems. That is, when the magnetic layer contains a noble metal, the use of an expensive noble metal increases the product cost.

In addition, in the method of heating the substrate to a high temperature, in a device which is usually used for mass production of magnetic recording media, the substrate is heated to a temperature of 250 ° C. or higher to form a magnetic layer. Have difficulty. Even if a device capable of heating the substrate to a temperature of 250 ° C. or higher is used, NiP is magnetized at a temperature of 280 ° C. or higher in a commonly used NiP / Al substrate. Therefore, the magnetic layer cannot be formed by heating the substrate to a temperature of 280 ° C. or higher.

Further, conventionally, since a NiP / Al substrate is usually used, it is not satisfactory in view of downsizing and large capacity of the recording apparatus, and a lighter and smoother substrate is required. is there. A glass substrate is a substrate that has better smoothness than the NiP / Al substrate. However, since glass is an insulator, it is not possible to form a magnetic layer while applying a bias voltage. Therefore, when the glass substrate is used, the coercive force of the magnetic layer cannot be sufficiently increased.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a magnetic recording medium which has a high coercive force and can achieve a higher recording density than ever before. To aim.

[0015]

A method of manufacturing a magnetic recording medium according to the first invention of the present application uses a sputtering method while applying a negative bias voltage to a substrate made of carbon heated to a predetermined temperature. The method is characterized by including a step of forming a magnetic material layer made of a Co-based alloy on a substrate and a step of forming a protective layer on the magnetic material layer.

In the method of manufacturing a magnetic recording medium according to the second invention of the present application, a negative bias voltage is applied to a substrate made of carbon heated to a predetermined temperature, and a sputtering method is used to form Cr on the substrate. Forming an intermediate layer, forming a magnetic layer made of a Co-based alloy on the intermediate layer by using a sputtering method while applying a negative bias voltage to the substrate, and forming a magnetic layer on the magnetic layer. And a step of forming a protective layer.

[0017]

The inventors of the present invention have a high coercive force even if an expensive noble metal is not included in the magnetic material layer, can achieve a high recording density, and can be manufactured by using a manufacturing apparatus that has been conventionally used. Various experimental studies were conducted to obtain a magnetic recording medium that can be used. As a result, they have found that an extremely excellent magnetic recording medium can be manufactured by using carbon as the substrate of the magnetic recording medium.

That is, since the carbon substrate is black, the surface temperature of the substrate becomes higher than that of the conventional NiP / Al substrate even when heated under the same conditions. Moreover, since carbon is a non-magnetic material, it does not magnetically affect the magnetic material layer even when heated to a high temperature. Furthermore, since carbon has high heat resistance, it does not easily deform even when heated to a temperature of 250 ° C. or higher. Furthermore, since carbon is a conductor, it is possible to form a magnetic layer while applying a bias voltage. Therefore, it is possible to form a magnetic layer made of a Co-based alloy on a substrate having a surface temperature higher than that of the conventional one and having a negative bias voltage applied. This makes it possible to obtain a magnetic layer having a higher coercive force than the conventional one.

The reason why the coercive force of the magnetic layer made of a Co-based alloy is improved by using a carbon substrate has not been fully clarified, but the magnetic layer is heated at a high temperature while applying a bias voltage to the substrate. It is considered that the magnetic separation of the crystal grains forming the magnetic layer proceeds by forming the.

The hardness Hv of carbon is as high as 650,
Conventionally, the smoothness is superior to that of aluminum alloy (Hv = 60) or NiP (Hv = 450) used as a substrate of a magnetic recording medium. Furthermore, the specific gravity of carbon is
Its weight is 1.5 to 2.0, which is lighter than aluminum (specific gravity 2.7) and its bending strength is as high as about 180MPa, which makes it possible to reduce the weight of the magnetic recording medium and reduce the load on the drive motor. ..

As described above, the carbon substrate is lightweight, has high strength, is excellent in smoothness, can apply a negative bias voltage when forming the magnetic layer, and further Since the surface temperature can be increased, it is extremely excellent as a substrate for magnetic recording media.

Although the magnetic layer may be directly formed on the carbon substrate, the crystal of the magnetic layer may be formed by interposing an intermediate layer of Cr (chrome) between the substrate and the magnetic layer. Is improved, and the coercive force of the magnetic layer can be further improved. Therefore, it is preferable to form an intermediate layer made of Cr on the carbon substrate and then form a magnetic layer on the intermediate layer.

[0023]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

1A and 1B are schematic cross-sectional views showing a method of manufacturing a magnetic recording medium according to the first embodiment of the present invention in the order of steps.

First, as shown in FIG. 1A, while applying a bias voltage of -100 to -300 V to the substrate 1 made of carbon and heating the substrate 1 to 250 ° C., for example,
The magnetic layer 3 made of a Co-based alloy such as CoNiCr is formed on the substrate with a thickness of, for example, 600Å by using the sputter method.

Then, as shown in FIG. 1 (b), a protective layer 4 made of carbon is formed on the magnetic layer 3, for example, 300Å.
Formed with a thickness of. As a result, the magnetic recording medium is completed.

According to the method of this embodiment, since the carbon substrate 1 is black, the surface temperature of the substrate 1 becomes high when the magnetic layer is formed. Since the magnetic layer is formed on the surface of the substrate while applying the bias voltage to the high temperature substrate, it is possible to obtain a magnetic layer having extremely high coercive force. Further, since the carbon substrate is lighter than the conventional NiP / Al substrate,
There is also an effect that the load on the drive motor can be reduced.

2A to 2C are schematic cross-sectional views showing a method of manufacturing a magnetic recording medium according to the second embodiment of the present invention in the order of steps.

First, as shown in FIG. 2A, while applying a bias voltage of, for example, -100 to -300 V to the carbon substrate 1a and heating the substrate 1a to, for example, 250 ° C., a sputtering method is used. An intermediate layer 2a made of Cr is formed on the substrate 1a with a thickness of 3000 Å, for example.

Next, as shown in FIG. 2 (b), a bias voltage of, for example, -100 to -300 V is applied to the carbon substrate 1a, and the substrate 1a is heated to, for example, 250.degree. A magnetic layer 3a made of a Co-based alloy such as CoNiCr is formed thereon with a thickness of 600 Å, for example.

Then, as shown in FIG. 2C, a protective layer 4a made of carbon is formed on the magnetic layer 3a, for example.
Form with a thickness of 00Å. As a result, the magnetic recording medium is completed.

In this embodiment, since the intermediate layer 2a made of Cr is formed between the substrate 1a and the magnetic layer 3a, the crystal orientation of the magnetic layer 3a is improved and the first embodiment is realized. The coercive force of the magnetic layer is improved as compared with the example.

Next, the results of actually manufacturing a magnetic recording medium by the method of this embodiment and examining its characteristics will be described in comparison with a comparative example.

First, a phenol-formaldehyde resin, which is a thermosetting resin that becomes vitreous carbon after carbonization and firing, is molded into a magnetic disk substrate shape, and then in a nitrogen atmosphere.
Pre-baking at a temperature of 1000 to 1500 ° C, then using a hot isostatic pressing (HIP) device while heating to 2500 ° C
HIP treatment was carried out by applying an isotropic pressure of 2000 atm. Then, the inner and outer peripheral end faces of the disk were processed and surface-polished to obtain a 3.5-inch substrate made of carbon and having a plate thickness of 1.27 mm.

Next, under the conditions shown in Table 1 below, an intermediate layer made of Cr (thickness: about 3000Å) and C on the carbon substrate
A magnetic layer (thickness: about 600Å) made of oNiCr and a protective layer (thickness: about 300Å) made of carbon were sequentially formed to manufacture a magnetic recording medium. The intermediate layer and the magnetic layer were formed while applying the bias voltage shown in Table 1 to the substrate. On the other hand, as a comparative example, a magnetic recording medium was manufactured in the same manner as in the above-described example except that a NiP / Al substrate was used.

[0036]

[Table 1]

The coercive force Hc of each magnetic recording medium of these examples and comparative examples was measured using a vibrating sample magnetometer. FIG. 3 is a graph showing coercive force measurement results of Examples and Comparative Examples in which the horizontal axis represents the bias voltage applied to the substrate and the vertical axis represents the coercive force Hc. As is clear from FIG. 3, the magnetic recording medium of the example was able to obtain a higher coercive force with the same bias voltage than the magnetic recording medium of the comparative example.

Next, in order to investigate the cause of this, the surface temperature reached during the formation of the intermediate layer and the magnetic layer was measured using a thermocouple. The results are shown in Table 2 below.

[0039]

[Table 2]

As is clear from Table 2, the carbon substrate (Example) is NiP / Al even when heated under the same conditions.
The surface arrival temperature is higher than that of the substrate (comparative example). That is, in the case of a carbon substrate, since the intermediate layer and the magnetic layer are formed while the substrate surface is at a high temperature, magnetic separation of the crystal grains forming the magnetic layer is greater than that of the NiP / Al substrate. It is considered that the coercive force of the magnetic layer increases as the magnetic field progresses.

Even in the magnetic recording medium having no intermediate layer, the coercive force of the magnetic recording medium was improved when the carbon substrate was used as compared with when the NiP / Al substrate was used. Further, as the magnetic layer, CoCrTa, CoCr
The same effect as that of the above-described embodiment was obtained also when the magnetic body made of another Co-based alloy such as Pt and CoCr was used. Further, the material of the protective layer may be other than carbon.

[0042]

As described above, according to the present invention, a negative bias voltage is applied to a carbon substrate heated to a predetermined temperature, and a magnetic layer made of a Co-based alloy is directly or from Cr on this substrate. Since it is formed via the intermediate layer, the magnetic recording medium having a higher coercive force and lighter weight than the conventional one can be obtained. Therefore, the magnetic recording medium manufactured by the method of the present invention has an effect of being able to cope with a higher recording density and a load on the drive motor can be reduced as compared with the conventional one.

[Brief description of drawings]

1A and 1B are schematic cross-sectional views showing a method of manufacturing a magnetic recording medium according to a first embodiment of the invention in the order of steps.

2A to 2C are schematic cross-sectional views showing a method of manufacturing a magnetic recording medium according to a second embodiment of the invention in the order of steps.

FIG. 3 is a graph showing coercive force measurement results of Examples and Comparative Examples.

[Explanation of symbols] 1,1a; carbon substrate 2a; intermediate layer 3, 3a; magnetic layer 4, 4a; protective layer

Claims (2)

[Claims] 1. A step of applying a negative bias voltage to a substrate made of carbon heated to a predetermined temperature and forming a magnetic layer made of a Co-based alloy on the substrate by using a sputtering method, and the magnetic layer. And a step of forming a protective layer on the body layer. 2. A step of applying a negative bias voltage to a substrate made of carbon heated to a predetermined temperature and forming an intermediate layer made of Cr on the substrate by using a sputtering method, and a step of forming a negative layer on the substrate. The method has a step of forming a magnetic layer made of a Co-based alloy on the intermediate layer by using a sputtering method while applying a bias voltage, and a step of forming a protective layer on the magnetic layer. And a method for manufacturing a magnetic recording medium.