JPS61133031A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To form effectively a plasma oxidation layer and a to improve the durability and running property of the resultant magnetic recording medium by subjecting the surface of the magnetic layer of the magnetic recording medium to the plasma oxidation while maintaining the magnetic recording medium at negative potential in the stage of subjecting said surface to the plasma oxidation treatment. CONSTITUTION:Any magnetic recording medium constituted by depositing directly a ferromagnetic metallic material on a non-magnetic substrate and forming a thin metallic film thereon as the magnetic layer is acceptable as the magnetic recording medium. Said medium is therefore applicable to, for example, a magnetic recording medium for vertical magnetic recording or so-called thin ferromagnetic metallic film type magnetic recording medium, etc. In practical treatment, the air in a reaction chamber 6 is thoroughly removed by a vacuum pump, etc. and the pressure therein is reduced to about 10<-2>Torr and thereafter gaseous oxygen is introduced into the chamber 6. While the gaseous oxygen is then introduced into the chamber 6 at a prescribed flow rate, a high-frequency power source 7 is operated to charge electrostatically the magnetic recording medium 4 to the negative potential. The magnetic recording medium of which the surface of the magnetic layer 3 consisting of the thin metallic film is subjected to the plasma oxidation is thus obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a metal thin film type magnetic recording medium used as a high-density magnetic recording medium. This invention relates to improvements in surface treatment methods for magnetic layers.

[Conventional technology]

In the field of magnetic recording, higher density recording of recording signals and shorter recording wavelengths are progressing, and in response to this, magnetic recording media with large coercive force Hc and residual magnetic flux density Br are required. There is.

Therefore, conventionally, for example, polyester film, etc.

A ferromagnetic metal WI film is formed by directly depositing a ferromagnetic metal material such as a Co-Ni alloy on a non-magnetic support using a method such as a vacuum evaporation method or a sputtering method, and this is used as a magnetic layer. Metal thin film magnetic recording media have been proposed. This ferromagnetic metal thin film type magnetic recording medium not only has high coercive force Hc and residual magnetic flux density Br, but also allows the depth of the magnetic layer to be made extremely thin, so recording demagnetization and thickness loss during reproduction are extremely small. It has many advantages in terms of magnetic properties, such as being able to increase the packing density of ferromagnetic materials.

Alternatively, Co
A perpendicular magnetization recording type magnetic recording medium has also been proposed in which a magnetic layer is formed by directly depositing a -Cr alloy using a vacuum evaporation method, and recording is performed by magnetizing the magnetic layer in the thickness direction. In this perpendicular magnetization recording type magnetic recording medium,
As the recording wavelength becomes shorter, the demagnetizing field becomes smaller, so the recording density can be dramatically increased, and it is known that this is particularly advantageous for short wavelength recording and high density recording. .

By the way, in a magnetic recording medium whose magnetic layer is a metal IFM deposited by a vacuum evaporation method as described above,
Although progress has been made to smooth the surface from the standpoint of spacing loss, etc., this has caused problems with the durability, runnability, etc. of the magnetic recording medium, and improvement thereof has become a major issue.

For example, attempts have been made to improve the durability, runnability, etc. of the magnetic recording medium by coating the surface of the magnetic layer, ie, the metal thin film, with a lubricant or the like to form a protective shell. However, in this case, the coefficient of friction is initially reduced and running properties are improved, but since the adhesion of the lubricant to the thin metal film is weak, this lubricant is gradually scraped off by a magnetic head, etc. There are many problems in terms of durability, uniformity, film thickness, etc., and the effectiveness decreases rapidly.

On the other hand, a method has been proposed for improving the durability of the magnetic recording medium while suppressing spacing loss by oxidizing the surface of the metal thin film by plasma oxidation and forming an extremely thin oxide layer on the surface of the metal thin film. There is.

However, in the above method, plasma oxidation treatment is performed by simply arranging electrodes connected to a high-frequency power source and the magnetic recording medium facing each other, so that plasma oxidation does not proceed effectively. For this reason, a sufficient plasma oxide film is not formed, and the above-mentioned requirements for durability of the magnetic recording medium cannot be satisfied. Furthermore, when the electrodes and the magnetic recording medium are disposed facing each other, the discharge voltage for the plasma oxidation treatment must be increased to a certain extent, so that the surface of the magnetic recording medium is etched by the oxygen plasma. This prevents improvements in durability, etc.

[Problem that the invention seeks to solve]

As described above, in the conventional plasma oxidation treatment, effective surface oxidation cannot be performed, and there are problems with the durability and runnability of the resulting magnetic recording medium.

Therefore, the present invention was proposed in order to eliminate the drawbacks of the above-mentioned conventional methods, and it is possible to effectively perform plasma oxidation while suppressing surface etching in plasma oxidation treatment of the surface of a magnetic layer. An object of the present invention is to provide a method for manufacturing a magnetic recording medium that can manufacture a magnetic recording medium with excellent durability and running performance.

[Means for solving problems]

The present invention was proposed in order to eliminate the drawbacks of the above-mentioned conventional methods, and involves forming a magnetic layer made of a ferromagnetic metal thin film on a non-magnetic support, and maintaining the magnetic layer at a negative potential. This method is characterized by plasma oxidation of the layer surface.

[Effect]

Therefore, according to the present invention, when plasma oxidizing the magnetic layer surface of a magnetic recording medium, the plasma oxidation is performed while keeping the magnetic recording medium at a negative potential, so that oxygen plasma is actively directed toward the magnetic recording medium. The particles are accelerated and collided with each other, effectively progressing plasma oxidation. Furthermore, since there is no need to make the discharge potential very high, surface etching hardly progresses.

〔Example〕

The manufacturing method of the present invention will be explained in detail below.

The present invention can be applied to any magnetic recording medium as long as it is a magnetic recording medium in which a ferromagnetic metal material is directly deposited on a non-magnetic support and gold ma*i'* is formed as a magnetic layer. It may be. Therefore, it is applicable to, for example, magnetic recording media for perpendicular magnetic recording, so-called ferromagnetic metal III type magnetic recording media, and the like.

As the ferromagnetic metal material constituting the magnetic layer of the magnetic recording medium for perpendicular magnetic recording, for example, a Co--Cr alloy is used. For example, it contains 10 to 25 at% Cr and the balance is CO.
A magnetic layer with excellent vertical orientation can be formed by depositing a Co--Cr alloy consisting of the following by sputtering or vacuum evaporation.

On the other hand, the ferromagnetic metal materials used for the magnetic layer of the ferromagnetic metal thin film magnetic recording medium include iron Fe, cobalt C
o, metal such as nickel Ni or Go-Ni alloy, F
e -Co alloy, Fe-Ni alloy, Co-Ni -Fe
-B alloys and other alloys are mentioned.

Further, examples of the means for depositing the ferromagnetic metal material include vacuum evaporation, ion blasting, sputtering, and the like. In the vacuum evaporation method, the ferromagnetic metal material is evaporated under a vacuum of 10 to 10 Torr by resistance heating, high frequency heating, electron beam heating, etc., and the evaporated metal (ferromagnetic metal material) is deposited on a nonmagnetic support. It is said to be deposited,
It is broadly divided into oblique evaporation method and vertical evaporation method. The above-mentioned oblique deposition method is a method in which the ferromagnetic metal material is deposited obliquely on a non-magnetic support in order to obtain a high coercive force, and in order to obtain a higher coercive force, the ferromagnetic metal material is vapor-deposited in an oxygen atmosphere. It also includes those that perform vapor deposition. In the vertical deposition method, Bi and Tβ are deposited on a non-magnetic support in advance in order to improve deposition efficiency and productivity and obtain high coercive force.

A base metal layer such as Sb, Ga, Ge, etc. is formed,
The above-mentioned ferromagnetic metal material is vertically deposited on this base metal layer. The above-mentioned ion brating method is also a type of vacuum evaporation method, in which DC glow discharge and RF glow discharge are caused in an inert gas atmosphere of 10 to 10 Torr, and the above-mentioned ferromagnetic metal is evaporated during the discharge. The above sputtering method causes glow discharge in an atmosphere containing argon gas as a main component at 10 to 10 Torr, and uses the generated argon ions to knock out atoms on the target surface. Examples include polar sputter freezing, high frequency sputtering, and magnetron sputtering using magnetron discharge.

The present invention is further characterized in that the surface of the metal Wt film is subjected to plasma oxidation treatment while maintaining the magnetic recording medium at a negative potential.

The reaction equipment used for the above plasma oxidation treatment is as follows:
For example, an apparatus as shown in FIG. 1 is used.

The above reaction apparatus is equipped with a reaction chamber 6 for plasma oxidation reaction, and a non-magnetic support 2 is provided inside the reaction chamber 6.
A magnetic recording medium 4, on which a magnetic layer 3 made of a ferromagnetic metal thin film is formed, is bonded to and mounted on an electrode 5. Here, the magnetic recording medium 4 is arranged so that the surface of the magnetic layer 3 is exposed to an oxygen atmosphere.

Further, the electrode 5 is connected to the negative side of a high frequency power source 4 (oscillation frequency is 13.56 MHz) located outside the reaction chamber 6, so that the magnetic recording medium 4 is charged to a negative potential. . Further, an oxygen gas source 1 is connected to the reaction chamber 6 through an introduction pipe, so that oxygen gas can be supplied into the reaction chamber s.

Using the reaction apparatus configured as described above, first, the air in the reaction chamber 6 is sufficiently removed using a vacuum pump etc.
The pressure is reduced to about 0 Torr, and then oxygen gas is introduced into the reaction chamber 6.

Next, while introducing the oxygen gas into the reaction chamber 6 at a predetermined flow rate, the high frequency power source 7 is operated to charge the magnetic recording medium 4 to a negative potential. In this case, the inside of the reaction chamber 6 is generally kept at a pressure of 10 to 3 Torr in order to cause good discharge.
It is preferable to conduct the test in a vacuum of about 10 T.
orr level is adopted.

Through the above steps, a magnetic recording medium in which the surface of the magnetic layer 3 made of a metal thin film is plasma oxidized is obtained.

Note that if the treatment time in the plasma oxidation treatment is too short or the discharge voltage is too low, the plasma oxidation layer becomes thin and the durability of the magnetic recording medium deteriorates. Furthermore, if the treatment time in the plasma oxidation treatment is too long or the discharge voltage is too high, the surface of the magnetic layer 6 made of a ferromagnetic metal thin film will be etched, which will also deteriorate the durability and running properties of the magnetic recording medium. . According to the experiments conducted by the present inventors, in order to effectively oxidize the surface without progressing the surface etching, the discharge voltage must be set at 100 to 50%.
It has been found that the plasma oxidation treatment can be performed by setting the discharge time to within 5 minutes and setting the discharge time to within 5 minutes.

Next, examples of the present invention will be described in more detail, but it goes without saying that the present invention is not limited to these examples.

Example 1 Diameter 860. A Co--Cr alloy was deposited on a base film having a thickness of 50 μm by sputtering to form a magnetic layer, and then plasma oxidation was performed using the reaction apparatus shown in FIG. 1 to obtain a floppy sheet medium.

Note that the conditions for plasma oxidation were as follows.

High frequency power supply oscillation frequency: 13.56 MHz Discharge voltage: 300V Discharge power: 20W Reaction chamber vacuum: 0.05 Torr Discharge time
...The still time of the Fronby sheet medium obtained for 2 minutes was measured. The results are shown in Table 1. For comparison, the still time before plasma oxidation treatment is also shown.

In addition, the above-mentioned still time indicates the time from when a signal with a wavelength of 1μ is recorded on a floppy sheet medium until the reproduction output (RMS) decreases, and is a measure of the durability of the magnetic recording medium. It is.

Table 1 This Table 1 shows that even with floppy sheet media (still time 0 minutes), which had no durability at all because it was too smooth, it became possible to make it durable for about 5 hours, and plasma oxidation treatment was applied. It can be seen that this significantly improves durability.

In addition, after producing a similar floppy sheet medium using a base film having the same smoothness as in the above example, the plasma oxidation treatment conditions were changed, that is, the discharge voltage was set to exceed 5oov, the discharge The still time was measured when the time was set to 5 minutes or more. As a result, it was found that the still time was reduced compared to the case where the plasma oxidation treatment conditions were optimal as in Example 1 above. this is,
This is because the etching of the surface of the floppy sheet medium progresses as the discharge time becomes longer and the discharge voltage becomes thicker, and this phenomenon can be observed using a scanning electron microscope.

Example 2 A Co-Cr alloy was deposited by sputtering on a base film with a diameter of 86fi and a thickness of 50μ (the surface roughness was somewhat rougher than that of Example 1), and the film thickness was 0.4μ. After forming the magnetic layer, plasma oxidation was performed under the same conditions as in Example 1 to obtain a floppy sheet medium.

The still time of the obtained floppy sheet medium was measured. The results are shown in Table 2. For comparison, the still time before plasma oxidation treatment is also shown.

Table 2 From this Table 2, by applying plasma oxidation treatment,
It can be seen that the still time for floppy sheet media is significantly longer.

In each of the above examples, when the surface treatment was performed under the above plasma oxidation conditions, it was confirmed by Kerr rotation angle measurement that there was no change in the magnetic properties of the ferromagnetic metal thin film, and that there was no increase in pacing loss. It was confirmed by measurements of actual recording and reproducing characteristics, and also by measurements using Talystep that there was no change in the surface properties of the ferromagnetic metal i film before and after the plasma oxidation treatment.

Comparative example! A Go-Cr alloy was deposited on a 486 tm, 50 μm thick base film by sputtering to form a magnetic layer, and then plasma oxidation was performed using the reaction apparatus shown in Figure 2 to form a floppy sheet medium. Obtained.

In this case, the floppy sheet media is not held at a negative potential. Note that the conditions for plasma oxidation were as follows.

High frequency power supply oscillation frequency...13.56 MHz Discharge voltage...400V Reaction chamber vacuum degree...0.04 Torr Discharge time
...The still time of the obtained floppy sheet medium was measured for L minutes and 30 seconds. The results are shown in Table 3. For comparison, the still time before plasma oxidation treatment is also shown.

Table 3 From Table 3, it can be seen that when the floppy sheet medium is not kept at a negative potential during the plasma oxidation treatment, the plasma oxidation treatment has almost no effect.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
When plasma oxidizing the magnetic layer surface of a magnetic recording medium, the plasma oxidation is performed while keeping the magnetic recording medium at a negative potential, so a plasma oxidation layer is effectively formed and the durability and running performance of the resulting magnetic recording medium are improved. It is possible to improve sexual performance.

In particular, the discharge voltage during plasma oxidation treatment should be set at 100 to 500.
■By setting the discharge time to within 5 minutes,
Etching of the surface of the magnetic primary layer can be further suppressed, and the durability of the resulting magnetic recording medium is improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an example of a plasma oxidation treatment apparatus used in the present invention, and FIG. 2 is a schematic diagram of a plasma oxidation treatment apparatus used in a comparative example. 2... Nonmagnetic support 3... Magnetic layer (metal thin l1l) 5... Electrode

Claims (1)

[Claims] A method for manufacturing a magnetic recording medium, which comprises forming a magnetic layer made of a ferromagnetic metal thin film on a nonmagnetic support, and subjecting the surface of the magnetic layer to plasma oxidation while maintaining the magnetic layer at a negative potential.