JP2001110051A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

(57) [Problem] To provide an amorphous perpendicular magnetic recording medium having both high coercive force and high saturation magnetization. SOLUTION: A DC bias voltage is applied to a substrate when forming a magnetic layer composed of a rare earth-transition metal amorphous film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium having perpendicular magnetic anisotropy used for magnetic recording.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for higher density and higher storage capacity in magnetic recording devices such as magnetic disks. With such an increase in recording density, the size of recording bits has become smaller and closer to the dimensions of the crystal grains constituting the thin-film magnetic recording medium, and as a result, the crystal grains have such a size that they behave like a single magnetic domain. It is necessary to promote magnetic separation between them. Further, when the number of crystal grains included in one bit decreases, noise increases. Therefore, it is necessary to reduce the crystal grain size as the recording density increases. However,
When the crystal grains are too fine, instability of magnetization due to thermal fluctuations is caused.

[0003] The results of a computer simulation study of the thermal stability of recording magnetization based on a micromagnetics model have been reported ("Monte Carlo simulation of thermal fluctuations in perpendicular recording media and longitudinal recording media", Yasutarou Uesaka et al. IEICE Technical Report MR96-37 1
996-11).

According to this, in both the longitudinal magnetic recording and the perpendicular magnetic recording, the thermal stability index KuV /
It is said that when kT becomes 100 or less, the recording magnetization decreases. Where Ku is the magnetic anisotropic energy, V
Is the activation volume that is the unit of magnetization reversal, k is the Boltzmann constant, and T is the absolute temperature. Therefore, it is expected that a perpendicular magnetic recording medium, which can have a large medium thickness, is more advantageous for deterioration due to thermal fluctuation of recording magnetization.

[0005] Based on the above reported results, the results of studies on recording density characteristics, medium noise characteristics, and the like have been reported for perpendicular magnetic recording media of CoCrPt and CoCrPtTa alloy. Density Magnetic Recording ”Masaaki Nihon et al. Journal of the Japan Society of Applied Magnetics Vo
l. 21 No. 6 pp950-958 199
7) When the recording density is 30 to 40 Gb / in ² , KuV
The value of / kT increases to about 130 in perpendicular magnetic recording, while it increases to about 40 in longitudinal magnetic recording.

[0006]

However, further considerations are needed in view of the critical value of 100. In determining the value of KuV / kT, the value of Ku is determined by an experiment using a single crystal magnetic thin film, but the activation volume V is determined by the crystal grain size and the film thickness of the medium. Are used, and the reliability of the above values is considered to be insufficient. Further, in both the longitudinal magnetic recording medium and the perpendicular magnetic recording medium, as long as a crystalline material is used, if the crystal grain size is reduced to reduce the medium noise, the influence of thermal fluctuation increases. Problems are inherently difficult to avoid.

Accordingly, the present invention provides a method of manufacturing a magnetic recording medium which is less affected by thermal fluctuations in such a situation and can exceed the limit of the recording density of a conventional magnetic recording medium. The purpose is to:

[0008]

In order to solve the above problems, attention has been paid to an amorphous perpendicular magnetic recording medium. Since the amorphous material has no crystal grains, the activation volume V is not controlled by the particle size. Therefore, it is possible to have a large activation volume V, and it is expected that the material is less likely to be affected by thermal fluctuation as compared with a crystalline material.

A magneto-optical recording medium is well known as an amorphous perpendicular magnetic recording medium. However, in the magneto-optical recording medium, an alloy of a heavy rare earth metal and a 3d transition metal is used, and the coercive force H is adjusted by adjusting the compensation temperature to around room temperature.
c diverges and keeps record. Therefore, at room temperature, the magnetic moments of the heavy rare earth metal and the 3d transition metal cancel each other out, and the saturation magnetization Ms is small, so that the magnetic recording medium cannot be used for recording and reproduction with a magnetic head. This is because a magnetic recording medium recorded and reproduced by a magnetic head must have a large saturation magnetization and a certain coercive force at room temperature.

On the other hand, in an alloy of a light rare earth metal and a 3d transition metal, a large saturation magnetization Ms is obtained because the magnetic moments are coupled in parallel. Japanese Patent Application Laid-Open No.
An Nd ₁₅ Co ₈₅ amorphous alloy film is reported in an example of Japanese Patent No. 54358. However, although it has been reported that the use of such an alloy thin film reduces the medium noise, it does not describe the effect of thermal fluctuation.
Although there is no clear description in the specification, it is presumed to be an in-plane magnetic recording medium from the cause of the medium noise and the alloy composition described above.

As an amorphous perpendicular magnetic recording medium made of an alloy of a light rare earth metal and a 3d transition metal, PrCo has been reported as an example (“MAGNETIZATION,
CURIE TEMPERATURE AND PER
PENDICULAR MAGNETIC ANISO
TROPY OF EVAPORATED Co-RA
RE EARTH AMORPHOUS ALLOY
FILMS "M. TAKAHASHI et al.
J. MAGNETIZM AND MAGNETIC
MATERIALS Vol. 75 pp252-26
2 1988). However, when a magnetic recording medium was actually prepared and the characteristics of PrCo described above were measured, the coercive force Hc was as small as about 200 Oe in the entire composition region that was amorphous and exhibited perpendicular magnetic anisotropy. It could not be used as a medium.

As a result of further study on such a situation, a method for increasing the coercive force Hc without lowering other characteristics was found.

That is, the method for manufacturing a magnetic recording medium of the present invention is characterized in that a perpendicular magnetic anisotropic magnetic recording layer made of a rare earth-transition metal amorphous film is formed while applying a bias voltage to a substrate. It is assumed that.

Further, the invention is characterized in that the bias voltage is a DC bias voltage in a range of -50 V to +50 V.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. Here, the description will be made using Pr as the light rare earth metal, Tb as the heavy rare earth metal, and Co as the 3d transition metal.

FIG. 1 is a diagram showing the configuration of a perpendicular magnetic recording medium according to the present invention.

As shown in FIG. 1, the perpendicular magnetic recording medium
A magnetic recording layer (magnetic layer) 2 and a protective film 3 are sequentially laminated on a substrate 1. A glass substrate (Corning Co., # 7622) is used as the substrate 1. After evacuation to 3 × 10 ⁻⁷ Torr or less, the magnetic layer 2 and the protective film 3 are sequentially formed in the same vacuum. Here, a PrTbCo alloy film was used as the magnetic layer 2, and a Ta film was used as the protective film 3. In addition,
The composition of the PrTbCo alloy film used here was Pr ₇ Tb
₁₀ Co ₈₃ was formed using a composite target in which Pr and Tb pellets were arranged on a Co target.

Next, a method and conditions for forming the PrTbCo alloy film and the Ta film will be described.

For both the PrTbCo alloy film and the Ta film, a DC magnetron sputtering method was used, and an Ar gas pressure = 5.
Assuming that mTorr is constant, the PrTbCo alloy film is Powe
r = 620 mW / cm ² , Power of the Ta film is 86 m
The film was formed under the film forming condition of W / cm ² . At that time, PrTbC
Only when an o-alloy film is formed, the surface of the substrate 1 is changed from -100 V to +
A DC (direct current) bias voltage of 100 V was applied. The thickness of the PrTbCo alloy film was about 600 °, and the thickness of the Ta film was 100 °.

Therefore, PrTb formed by the above-described method is used.
Vertical coercive force Hc⊥ and saturation magnetization M of Co alloy film
2 and 3 show the dependence of s on the substrate applied DC bias voltage, and FIG. 4 shows the dependence of the perpendicular magnetic anisotropy K⊥ of the PrTbCo alloy film on the substrate applied DC bias voltage.

As shown in FIG. 2, Hc⊥ of the PrTbCo alloy film is large even when no bias voltage is applied,
Further, the DC bias voltage applied to the substrate is from -50 V to +50.
In the range of V, the coercive force Hc in the vertical direction is larger than when no bias voltage is applied. However, when the positive and negative DC bias voltages are further applied, the coercive force Hc # in the vertical direction becomes smaller than when no bias voltage is applied.

As shown in FIGS. 3 and 4, the saturation magnetization Ms and the perpendicular magnetic anisotropy K⊥
Almost no change due to bias voltage application is observed.

As described above, by applying a DC bias voltage of −50 V to +50 V to the substrate during the formation of the PrTbCo alloy film, the coercive force Hc⊥ in the vertical direction can be increased without lowering other characteristics. This makes it possible to produce a perpendicular magnetic recording medium having better thermal stability than a conventional crystalline medium.

A feature of the present invention is that, in a rare earth-transition metal amorphous film which has a large saturation magnetization but does not have a sufficient coercive force, a high saturation voltage can be obtained by applying a bias voltage to the substrate when forming a magnetic layer. The object is to achieve both magnetization and high coercive force.

Materials for the rare earth-transition metal amorphous film are disclosed in Japanese Patent Application Nos. 11-181040 and 11-181.
No. 041 and Japanese Patent Application No. 11-264961 have already been filed. Therefore, the above-described PrT
The present invention is not limited to the bCo alloy film. Light rare earth metals other than Pr (for example, Ce, Nd, Sm), heavy rare earth metals other than Tb (Gd, Ho, Er, Dy), and 3d transition metals other than Co ( Fe) may be used, and the same effect can be obtained.

In the above description, a Ta film was used as the protective film 3. However, other inorganic materials such as carbon and alumina can be used, and it is apparent that the film thickness may be other than 100 °.

Further, it is also possible to form a lubricating layer thereon and use it. Further, an antioxidant layer or the like can be added between the substrate 1 and the magnetic layer 2.

Although a glass substrate is used as the substrate 1 in the above description, another substrate such as an aluminum alloy, ceramics, or plastic, or a substrate subjected to a surface treatment may be used. Further, not only a rigid substrate such as a glass substrate but also a flexible substrate can be used.

As another example of the perpendicular magnetic recording medium,
A medium in which another magnetic layer is formed between the substrate 1 and the magnetic layer 2 and the magnetic layer 2 serving as a recording layer is sandwiched between the magnetic head and the other magnetic layer can be considered. The other magnetic layers have N
An i-Fe alloy film, a Co-Fe alloy film, an Fe-Al-Si alloy film, a Co-Zr-Nb alloy film, or the like is used.

By doing so, it is possible to perform steep recording in the vertical direction even when a ring type magnetic head is used for recording. Also, when a single pole head is used for recording, the other magnetic layer plays the role of the second magnetic pole, so that the leakage of the magnetic field in the track width direction is smaller than when a ring magnetic head is used. Thus, the track pitch can be reduced, and the recording density can be further increased.

[0031]

As described above, according to the present invention, PrTbC
By applying a bias voltage to the substrate during the formation of the o-alloy film, it is possible to increase the coercive force in the vertical direction without lowering other characteristics, and to achieve a higher thermal conductivity than the conventional crystalline medium. A perpendicular magnetic recording medium with excellent stability can be produced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a magnetic recording medium according to the present invention.

FIG. 2 is a diagram showing the dependency of Hc⊥ of a PrTbCo alloy film on a DC bias voltage applied to a substrate.

FIG. 3 is a diagram illustrating the dependence of Ms of a PrTbCo alloy film on a DC bias voltage applied to a substrate.

FIG. 4 is a diagram showing the dependence of K⊥ of a PrTbCo alloy film on a DC bias voltage applied to a substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Magnetic recording layer (magnetic layer) 3 Protective film

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Hidekazu Hayashi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation F-term (for reference) in the CAP Co., Ltd. 5D112 AA05 BB01 FA04 FB26

Claims (1)

[Claims] 1. A method for manufacturing a magnetic recording medium, comprising forming a perpendicular magnetic anisotropic magnetic recording layer comprising a rare earth-transition metal amorphous film while applying a bias voltage to a substrate. 2. The method according to claim 1, wherein the bias voltage is from -50 V to +5.
2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the DC bias voltage is in a range of 0V.