JPH03205616A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve coercive force by successively forming a Co-alloy magnetic layer and protective lubricating layer on a carbon substrate, and heating the medium at specified temp. CONSTITUTION:A Co-alloy magnetic layer 3 such as Co-Ni-Cr, Co-Ni, etc., and protective lubricating layer 4 are successively formed on a carbon substrate 1. By heating this medium at 250-1,450 deg.C in an atmospheric environment, interfaces of grains in the Co-alloy magnetic layer 3 are selectively oxidated, and segregation of Cr on the interfaces is promoted if the Co-alloy magnetic layer 3 contains Cr. Thereby, each grain of the Co-alloy magnetic layer 3 behave as a single magnetic domain, which increases the coercive force.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a magnetic recording medium that has a magnetic layer on a carbon substrate and is used in magnetic disk devices, etc. The present invention relates to a method of manufacturing a magnetic recording medium that allows for the production of magnetic recording media. [Prior Art] As is well known, the recording density of magnetic recording media such as magnetic disks is increasing. Generally, a factor that determines the performance of a magnetic recording medium is the magnetization transition width a (μm) expressed by the following equation (2).

accδ・Br/ (m-Hc) −■ However, δ is the magnetic layer thickness (μm), and Br is the residual magnetic flux density (G
), m is a factor related to squareness, Hc is coercive force (Oe)
It is. In order to improve the recording density, it is necessary to reduce the value of the magnetization transition width a expressed by the above equation, and effective means include making the magnetic layer thinner and increasing the coercive force. Therefore, conventionally, the method described below has been adopted as a method for increasing the coercive force. Namely, 7-Fe. In a coating type medium in which Os acicular magnetic particles, Altos powder, and a binder are kneaded and coated on an aluminum alloy substrate by a spin coating method, 1-Fe20. The acicular particles are made finer, or Co is deposited on the surface of the γ-Fezes.

In addition, on a substrate having a NiP plating layer on the surface of an aluminum alloy substrate (hereinafter referred to as a NiP plating substrate),
In plated thin film media in which a magnetic layer of Co--P, Co--Ni--P, etc. is formed by electroless plating, certain improvements have been made in the plating bath structure.

Furthermore, Co-Ni-Cr, C
In Supanota thin film media in which a magnetic layer such as o-Ni is formed by sputtering, the magnetic composition has been improved. In addition, there are methods for coating magnetic materials with the substrate heated to a high temperature (for example, Ishikawa et al., 11th Japanese Society of Applied Magnetics, Abstracts of Academic Conferences, P18, 1987, 11), and methods for applying a reverse high-ass voltage to the substrate. A method has been proposed in which the shape conditions of the magnetic layer are optimized (for example, Hashimoto et al., Proceedings of the 35th Applied Physics Association Conference, p. 57, 1988, 10). This method is used to increase the coercive force and increase the recording density, but due to the difficulty of thinning the film in coated media, magnetic layers formed by sputtering the magnetic material layer have been developed. The recording medium is expected to be used as a high-density magnetic recording medium.

On the other hand, in order to achieve high recording density, in addition to improving the coercive force mentioned above, the substrate must have a surface texture with low surface roughness and no surface defects, and chemical It is required to be physically stable, and to have hardness and strength that can ensure durability in contact with the head. Further, properties required of the substrate material include non-magnetism, high hardness, heat resistance, light weight, strength and rigidity.

In order to meet such demands regarding substrates, magnetic recording media using carbon substrates (glassy carbon substrates) as substrates have recently been proposed.
No. 234232 discloses a magnetic disk in which a magnetic thin film is formed on a glassy carbon substrate. The present applicant has also proposed a magnetic recording medium in which a Co-based alloy thin film is formed on a glassy carbon substrate (Japanese Patent Application No. 1-188225). [Problems to be Solved by the Invention] In the above-mentioned prior art, in the method of improving the magnetic composition in the sputtered thin film type medium, Co-
Since noble metals such as Cr-Pt are used, this is not economically desirable. On the other hand, magnetic recording media with improved coercive force have been obtained by high-temperature film formation methods in which a magnetic layer is formed by sputtering while the substrate is heated to a high temperature, but the carrier for holding the substrate is heated. Due to problems with the film assembly, such as the possibility of deformation, it is not easy to control the shape of the magnetic layer when the substrate heating temperature exceeds 250° C. when mass production is performed rather than at a research level. Furthermore, NiP
When using a plated substrate, if the temperature exceeds 280°C, the NiP plating layer will magnetize beyond the specification limit, which will have an adverse effect on the magnetic layer, and if it is heated to above 300°C, the substrate will deform. There is a problem with that.

In addition, magnetic recording media with improved coercive force have been obtained by forming the magnetic layer while applying a reverse bias voltage to the substrate, but since it is necessary to apply a reverse bias voltage, The disadvantage is that the structure of the device is complicated. Under these circumstances, the present inventors have repeatedly conducted research on increasing the coercive force of magnetic recording media, focusing on the characteristics of the carbon substrate described above, especially its heat resistance. It was discovered that the coercive force could be improved by forming a magnetic layer and the like and then heating it to a high temperature, leading to the present invention.

That is, an object of the present invention is to provide a method for manufacturing a magnetic recording medium that can improve coercive force when manufacturing a magnetic recording medium using a carbon substrate.

[Means to solve the problem]

In order to achieve the above object, a method for manufacturing a magnetic recording medium according to the invention of claim 1 is a method for manufacturing a magnetic recording medium having a magnetic layer made of a Co-based alloy and a protective lubricant layer in this order on a carbon substrate. The method is characterized in that after forming both the layers on the carbon substrate, this is heat-treated at a temperature of 250 to 1450°C. Further, a method for manufacturing a magnetic recording medium according to the invention of claim 2 is a method for manufacturing a magnetic recording medium having a base layer made of Cr, a magnetic layer made of a Co-based alloy, and a protective lubricant layer in this order on a carbon substrate. The method is characterized in that after each layer is formed on a carbon substrate, it is heat-treated at a temperature of 250 to 1450°C.

[For production]

In the invention of this application, the mechanism by which the coercive force is improved by the heat treatment described above is not necessarily clear, but it is presumed as follows.

In the method for manufacturing a magnetic recording medium according to the invention of claim 1, Co-Ni-CrSCo-Ni, Co-Ni-CrSCo-Ni,
Co-Ni-Pt, Go-Cr, or Co-C
When a magnetic layer made of a CO-based alloy such as r-Ta and a protective lubricant layer are sequentially formed and then heated at high temperature in the air, the grain boundaries of the Co-based alloy magnetic layer are selectively formed. In a Co-based alloy magnetic layer that further contains Cr, Cr
The segregation of particles to grain boundaries is promoted. As a result, it is thought that the coercive force is improved because the crystal grains of the CO-based alloy magnetic layer themselves behave as single-domain grains. Furthermore, when heating at high temperatures in vacuum or in an inert gas atmosphere, it is thought that coercive force is improved by promoting the segregation of Cr to the grain boundaries in the Co-based alloy magnetic layer. ．． On the other hand, in the method for manufacturing a magnetic recording medium according to the invention of claim 2, after sequentially forming a Cr underlayer, a CO-based alloy magnetic layer, and a protective lubricant layer on a carbon substrate, this is heat-treated. In addition to the effect of improving the coercive force, the (110) plane of the crystal lattice of the Cr underlayer is lengthened by the heat treatment, and the easy axis of magnetization (C axis) of the Co-based alloy magnetic layer is easily oriented in-plane. It is thought that the coercive force is improved.

Further, in this invention, the range of heat treatment temperature is 250°C.
The optimal temperature is about 1450°C, preferably about 350 to 800°C. This is because at a temperature lower than 250°C, the effect of improving coercive force is not sufficiently exhibited, and at a temperature exceeding 1450°C, the Co-based alloy magnetic layer itself may be destroyed by heat. [Examples] The present invention will be described below based on Examples.

Toyoha Tamadoko: First, to explain the production of carbon substrates for magnetic disks, phenol-formaldehyde resin, a thermosetting resin that becomes vitreous carbon after carbonization, is shaped into the shape of a magnetic disk, and then N2 gas is applied. 1000 in the atmosphere
Pre-fire at a temperature of ~1500°C. This was then heated to 2500°C using a hot isostatic presser (HIP).
HIP by applying isotropic pressure of 2000 atm while heating to
Process. The obtained cylindrical body was subjected to predetermined peripheral edge processing and surface polishing to obtain a 3.5-inch magnetic disk substrate with a thickness of 1.27 mm. Then, under the following conditions, as shown in FIG. 1(a), a Cr underlayer 2, a CoNi
There are two types: one in which three layers, Cr magnetic layer 3 and C protective lubricant layer 4, are successively formed by the sputtering method, and one without Cr underlayer 2 as shown in Figure 1(b). After producing these, they were heat-treated in an air atmosphere at 250 to 450°C for 2 hours to produce magnetic disks. '-゛Scape device: D. C. Magnetron sputtering device substrate temperature: 250°C Structure: Carbon substrate/Cr layer (thickness: 0, 500, 1000, 2000, 3000)/CO&! ．．
sNiaocrt. S layer (thickness: 2,600 layers)/C layer (thickness: 300 layers) Heat treatment conditions: 250 to 450°C x 2 hours Next, the coercive force Hc of the obtained magnetic disk was measured using a vibrating sample magnetometer (VSM).
) was measured. The results are shown in Figure 2. In addition, in FIG. 2, the symbol ^S means no heat treatment. In addition, for comparison, a NiP plated substrate of the same size as a 3.5-inch carbon substrate (approximately 15 mm thick on an AI-Mg alloy substrate) was prepared.
Table 1 shows the results of measuring the relationship between the heat treatment conditions and the amount of magnetization using vSM, and also shows the relationship between the heating temperature and the amount of substrate deformation. The results of measurement using a surface strain meter (trade name: NIDEK, manufactured by NIDEK) are shown in FIG.

(Hereafter, blank space) Table 1 Notes (1) Br: Residual magnetic flux density (G), Bs: Saturation magnetic flux density (G) (2) Bs in the case of NiP plated substrate
<10 (G) is required.

As can be seen from Fig. 2, magnetic disks with high coercive force could be obtained for both configurations shown in Fig. 1 (a) and (b) by performing heat treatment in an atmospheric atmosphere. . Furthermore, as shown in Table 1 and Figure 3, conventional Ni
Whereas P-plated substrates are already magnetized at around 250°C and deform when heated above 300°C, carbon substrates do not become magnetized even when heated above 250°C.
It will not be deformed. In addition, when the heat treatment is performed in the air atmosphere as in this example, the progress of oxidation of the CO-based alloy magnetic layer, in this case CoNiCr magnetic material N3, causes other magnetic properties such as saturation magnetic flux density Bs, Since the residual magnetic flux density Br tends to decrease, the same coercive force Hc
When trying to obtain a high temperature, it is desirable to perform heat treatment at a high temperature and in a short time.

In this example, unlike the first example, a magnetic disk was fabricated by performing heat treatment in a vacuum.

That is, on a carbon substrate l prepared in the same manner as in the first embodiment, a Cr base layer 2 with a thickness of 3000 mm and a Cr base layer 2 with a thickness of 600 mm
Human CoNiCr magnetic layer 3 (set fi: Co*t.sN
isoCrt. After sequentially forming the C protective lubricant layer 4 and C protective lubricant layer 4 using a sputtering device, this is deposited in a vacuum as shown in FIG.
A magnetic disk was produced by heat treatment under the conditions of temperature and time shown in a). The degree of vacuum is 30 mTorr. Next, the coercive force Hc, saturation magnetic flux density Bs, squareness ratio S (=Br/Bs), and coercive force squareness ratio S (corresponding to m in formula ■) of the obtained magnetic disk were measured using VSM. did. Examples of these results are shown in FIGS. 4(a) to 4(a), respectively. FIG. 4(a) is a diagram showing the relationship between heat treatment conditions and coercive force Hc, FIG. 4(b) is a diagram showing the relationship between heat treatment conditions and saturation magnetic flux density Bs, and FIG. 4(C) is a diagram showing the relationship between heat treatment conditions and coercive force Hc. A diagram showing the relationship between the heat treatment conditions and the squareness ratio S, and FIG. 4(a) are diagrams showing the relationship between the heat treatment conditions and the coercive force squareness ratio S*. In each figure, the symbol AS indicates the measured value without heat treatment. By performing heat treatment in a vacuum in this way,
As can be seen from FIG. 4(a), under the conditions of this example, 5
In the heating temperature range of 00 to 550°C, the coercive force He
A magnetic disk with improved performance was obtained. In this case, as can be seen from FIGS. 4(B) and 4(A), there is no excessive oxidation phenomenon of the CoNiCr magnetic layer 3 that is likely to occur due to heat treatment in the atmosphere, so high recording density can be achieved. The residual magnetic flux density Br and coercive force squareness ratio SI, which are other necessary magnetic characteristic factors, maintain almost the values without heat treatment, and it is possible to improve the coercive force Hc without reducing these. did it.

In this example, the Cr base layer 2 was heat treated in a vacuum.
A magnetic disk without this was fabricated.

That is, a CoNiCr magnetic body 13 (&
II Precept: Coav. sNisocrt. s) and the C protective lubricant layer 4 are sequentially formed using a sputtering device, and then deposited in a vacuum at a vacuum degree of 30 mTorr as shown in Fig. 5 (
A magnetic disk was produced by heat treatment under the conditions of temperature and time shown in a).

Next, the coercivity He and saturation magnetic flux density Bs of the obtained magnetic disk were measured by VSM. These results,
FIG. 5(a) is a diagram showing an example of the relationship between heat treatment conditions and coercive force Hc, and FIG. 5(b) is a diagram showing an example of the relationship between heat treatment conditions and saturation magnetic flux density Bs. Note that in each figure, the symbol AS indicates a measured value without heat treatment.

In this way, the Cr underlayer 2 is formed on the carbon substrate 1 in vacuum.
Figure 5 (a) can also be achieved by heat treating a material without
), under the conditions of this example, it was possible to obtain a magnetic disk whose coercive force Hc increased as the heating temperature was raised.

Next, an example in which a magnetic disk was manufactured by performing heat treatment in an inert gas atmosphere will be described below. Star 11 members On a carbon substrate l prepared in the same manner as in the first example,
Cr base layer 2 with a thickness of 30ooλ and CoN with a thickness of 600mm
icr magnetic layer 3 (&Il precept: Cog. sNi
, Iocr7. , ) and the C protective lubricant layer 4 are sequentially formed using a spunter device, and then heat-treated in an Ar gas atmosphere (atmospheric pressure state B) under the temperature and time conditions shown in FIG. 6(a). A magnetic disk was created using the following steps. Next, the coercive force Hc, saturation magnetic flux density Bs, squareness ratio S, and coercive force squareness ratio S of the obtained magnetic disk were measured by VSM. Examples of these results are shown in Figures 6(a) to 6(d).
) is shown. Figure 6 {phrase is a diagram showing the relationship between heat treatment conditions and coercive force Hc, Figure 6 (b) is a diagram showing the relationship between heat treatment conditions and saturation magnetic flux density Bs, and Figure 6 (C) is a diagram showing the relationship between heat treatment conditions and coercive force Hc. FIG. 6A is a diagram showing the relationship between the processing conditions and the squareness ratio S, and FIG. 6A is a diagram showing the relationship between the heat treatment conditions and the coercive force squareness ratio S. Note that in each figure, the symbol AS indicates a measured value without heat treatment.

Even by performing heat treatment in an Ar gas atmosphere in this way, as can be seen from the above figures, the residual magnetic flux density Br
, without reducing the coercive force squareness ratio S ratio, the coercive force Hc
A magnetic disk with improved performance was obtained.

Further, in this embodiment, the heat treatment was performed in an Ar gas atmosphere, but in the method according to the present invention, the heat treatment was performed in an Ar gas atmosphere instead of the Ar gas atmosphere. It has been confirmed that the coercive force He can also be increased by performing heat treatment in a gas atmosphere.

In addition, in each of the above embodiments, an example of a magnetic disk in which a Cr underlayer and a Co-based alloy magnetic layer are formed by a sputtering method is shown, but in this invention, these can be formed by a method such as vapor deposition or plating. It can also be applied to magnetic disks using carbon substrates.

〔Effect of the invention〕

As explained above, in the method for manufacturing a magnetic recording medium according to the invention of claim 1, after forming a Co-based alloy magnetic layer and a protective lubricant layer on a carbon substrate in order,
By heat-treating at a temperature of 450°C, the crystal grains of the Co-based alloy magnetic layer themselves behave as single-domain grains, resulting in a magnetic recording medium with improved coercive force. In addition to the above-mentioned coercive force improvement effect, the method for manufacturing a magnetic recording medium according to the invention of claim 2 also improves the crystal lattice of the Cr underlayer formed between the force-bonded substrate and the Co-based alloy magnetic layer. Since the (110) surface is heat treated, CO
The axis of easy magnetization of the base alloy magnetic layer is more likely to be oriented in-plane, and a magnetic recording medium with improved coercive force can be obtained. Therefore, according to the present invention, it is possible to provide a magnetic recording medium that has a higher coercive force than the conventional one and is suitable for increasing recording density by using a simple means of heat treatment. This has the economical effect that a certain film device can be used as is, and also contributes to increasing the capacity of a magnetic disk device without increasing its size.

[Brief explanation of drawings]

Figures F (a) and (b) are explanatory diagrams of the cross-sectional structure of the magnetic disk according to the present invention; Figure 2 is a diagram showing an example of the relationship between heat treatment conditions and coercive force in the first embodiment; The figure shows an example of the relationship between the heating temperature and the amount of substrate deformation in a carbon substrate according to the present invention and a conventional NiP plated substrate. Figures 5(a) and 5(b) are diagrams showing an example of the magnetic properties of the magnetic disk with respect to the heat treatment conditions; FIGS. 6′vlJ(a) to FIG. 6 (The crests are diagrams showing an example of magnetic characteristics with respect to the heat treatment conditions of the magnetic disk in the fourth embodiment. 1.1 Carbon substrate, 'l-Cr underlayer, 3- --C
oN iCr magnetic layer, 4-C protective lubricant layer.

Claims (2)

[Claims] (1) In a method for manufacturing a magnetic recording medium having a magnetic layer made of a Co-based alloy and a protective lubricant layer on a carbon substrate in this order, after forming both the layers on the carbon substrate,
A method for manufacturing a magnetic recording medium, comprising heat treatment at a temperature of 50 to 1450°C. (2) An underlayer made of Cr and Co on the carbon substrate in this order.
A method for manufacturing a magnetic recording medium having a magnetic layer made of a base alloy and a protective lubricant layer, characterized in that after each layer is formed on the carbon substrate, it is heat-treated at a temperature of 250 to 1450°C. A method for manufacturing a magnetic recording medium.