JP2001110029A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the thickness of a protective film on a rare earth-transition metal amorphous film without lowering corrosion resistance. SOLUTION: A 2nd magnetic layer 3 comprising a Co- or Fe-based perpendicular magnetic recording film is interposed between a 1st magnetic layer 2 comprising an amorphous rare earth-transition metal film and a protective film 4. The thickness of the protective film can be reduced without lowering corrosion resistance and the objective high density perpendicular magnetic recording medium excellent in thermal stability can be obtained.

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 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.

Therefore, 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.

As the amorphous perpendicular magnetic recording medium, a magneto-optical recording medium is well known. 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, an example of PrCo has been reported ("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.

Usually, a protective film is provided on a magnetic recording medium for the purpose of protecting the magnetic film from sliding by a magnetic head. As this protective film, a C-based film formed by DC sputtering is most commonly used. In addition, a film obtained by adding hydrogen to a carbon protective film for improving durability, RF sputtering, A method of forming by a CVD method using a hydrocarbon gas and the like are known.

One of the techniques for realizing high-density magnetic recording is to make the distance between the magnetic film of the magnetic recording medium and the magnetic head smaller. The most effective means for reducing the distance between the magnetic film and the magnetic head is to reduce the thickness of the protective film.

However, if the thickness of the protective film is too thin, it is impossible to completely cover the fine irregularities on the surface of the magnetic recording medium, and the magnetic layer is exposed on the surface of the magnetic recording medium. As a result, the magnetic layer is partially oxidized, resulting in a decrease in magnetic properties and a decrease in lubricity, which causes a crash between the head and the disk.

In particular, when a rare earth-transition metal amorphous film is used for a magnetic recording medium, since the rare earth element is very easily oxidized, it is very difficult to reduce the thickness of the protective film while maintaining corrosion resistance. Have difficulty.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first invention is a magnetic recording medium having a magnetic layer and a protective film sequentially laminated on a substrate. The magnetic layer includes a first magnetic layer and a second magnetic layer from the substrate side, and the first magnetic layer has perpendicular magnetic anisotropy and includes light rare earth, heavy rare earth, and 3d transition metal. The magnetic recording medium is characterized by being an amorphous alloy to be produced.

According to a second aspect of the present invention, the second magnetic layer comprises a C layer.
The magnetic recording medium according to the first invention, which is a perpendicular magnetization film containing o or Fe.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[Embodiment 1] FIG. 1 is a structural view of a perpendicular magnetic recording medium of the present invention. As shown in FIG. 1, a perpendicular magnetic recording medium includes a first magnetic layer (magnetic recording layer) 2,
The magnetic layer (magnetic recording layer) 3 and the protective film 4 are sequentially laminated. A glass substrate (manufactured by Corning:
Using # 7622), the first magnetic layer 2, the second magnetic layer 3, and the protective film 4 were sequentially formed in the same vacuum after evacuation to 3 × 10 ⁻⁷ Torr or less.

Here, PrTbC is used as the first magnetic layer 2.
A CoCrPt alloy film was used as the o-alloy film and the second magnetic layer 3, and a C film was used as the protective film 4. The composition of each of the PrTbCo alloy film and the CoCrPt alloy film is Pr ₇ Tb ₁₀
Co ₈₃ and Co ₇₂ Cr ₁₀ Pt ₁₈ were prepared using a composite target in which Pr, Tb or Cr, Pt pellets were respectively arranged on a Co target. The composition of each alloy is not limited to the above.

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

Each of the films was formed using a DC magnetron sputtering method, and the Ar gas pressure was kept constant at 5 mTorr, and the PrT
Power = 62 for bCo alloy film and CoCrPt alloy film
0mW / cm ^2, C film was formed in the film formation conditions Power = 86mW / cm ^2. At this time, when the CoCrPt alloy film is formed, the crystal grain size and the magnetic anisotropy are controlled.
Film formation was performed while applying a bias voltage of −50 V.

For comparison, the perpendicular magnetic recording medium in which the CoCrPt alloy film as the second magnetic layer 3 was removed, that is, the first magnetic layer 2 and the protective film 4 were formed on the substrate 1 was also the same as above. The film was formed under the following film forming conditions.

The thickness of the PrTbCo alloy film is 500 ° for a PrTbCo single-layer magnetic recording medium, and 400 ° for the PrTbCo / CoCrPt laminated magnetic recording medium.
The t alloy film was formed as a laminated film of 100 °. The thickness of the C film was 20, 50, 100, and 200 °, respectively.

Since the PrTbCo single-layer film and the PrTbCo / CoCrPt laminated film obtained by the above-mentioned method are amorphous, the evaluation of the thermal stability index KuV / kT requires the activation volume V to be equal to the conventional value. Can not be evaluated from the crystal grain size. Therefore, the thermal stability was evaluated using the fluctuation field Hf obtained from the dependency of the remanence coercive force on the magnetic field application time. This is described in “CoCrTa”.
And Viscosity and Noise Characteristics of CoCrPt Thin Film Media "
Kazusuke Yamanaka et al. IEICE Technical Report MR95-13 1995-
06. In the case of the fluctuation field Hf, contrary to the case of the thermal stability index KuV / kT, it is considered that the lower the value, the better the thermal stability. The use of this method has the advantage that Hf can be determined directly from the measurement of macro magnetic properties without the need for micro measurements such as the crystal grain size.

First, Table 1 shows the saturation magnetization Ms, coercive force Hc, perpendicular magnetic anisotropy energy K⊥, and fluctuation field Hf of the PrTbCo single-layer magnetic recording medium and the PrTbCo / CoCrPt laminated film magnetic recording medium. For comparison, Table 1 also shows each characteristic of a conventional CoCrPt single-layer magnetic recording medium.

[0026]

[Table 1] As a result, the perpendicular magnetic anisotropy energy K⊥ of the magnetic recording medium of the PrTbCo single layer film is extremely large as 1 × 10 ⁷ compared to the conventional magnetic recording medium of the CoCrPt single layer film,
In addition, since the fluctuation field Hf is small, it is understood that it is suitable for high-density recording. This means that PrTbCo / CoCrP
The same applies to the magnetic recording medium of the t-layer film, and PrT
It can be determined that the deterioration of the magnetic characteristics due to the bCo / CoCrPt lamination is small.

Further, based on the above measurement results, the activation volume V (= kT / HfMs) is obtained from the measured value of the fluctuation field Hf, as in the case of the conventional crystalline medium, and the magnetic anisotropy energy Ku is obtained. When the value of KuV / kT is determined using the measured values of the above, the value of the conventional crystalline medium (CoCrPt: 40 to
60), a PrTbCo single layer magnetic recording medium of 3
Even with a magnetic recording medium of PrTbCo / CoCrPt laminated film of 2,000 or more, a very large value of about 2,000 was obtained. This also indicates that the magnetic stability of the PrTbCo single-layer magnetic recording medium and the magnetic recording medium of the PrTbCo / CoCrPt laminated film is extremely excellent.

Next, Table 2 shows the dependency of the corrosion resistance of the protective film on the magnetic recording medium of the PrTbCo / CoCrPt laminated film and the magnetic recording medium of the PrTbCo single layer film.
To examine the corrosion resistance, each thin film was immersed in a 1N saline solution for 20 minutes, then subjected to an aging treatment at 85 ° C. and 85% RH (relative humidity) for 3 hours, and observed for pitting corrosion using an optical microscope. By doing that. For comparison, the respective characteristics of the conventional CoCrPt film magnetic recording medium are also shown in the table.

[0029]

[Table 2] As a result, in the case of the magnetic recording medium of the PrTbCo single layer film, a large number of pitting corrosions were confirmed at the C film thicknesses of 20, 50, 100 and 200 °. Eating was confirmed to be the most advanced.
On the other hand, in the case of a magnetic recording medium having a PrTbCo / CoCrPt laminated film, pitting corrosion was scarcely observed when the thickness of the C film was 100 ° or more, and PrTbCo was observed even when the thickness was 50 ° or less.
The number and size of the observed pits were very small as compared with the case of the single layer film. In the case of a conventional CoCrPt film magnetic recording medium, pitting corrosion was hardly observed when the film thickness of the C film was 100 ° or more.

From the above results, by inserting a Co-based perpendicular magnetization film between the PrTbCo amorphous alloy film and the C protective film, the corrosion resistance is not reduced as compared with the case of the PrTbCo single layer film. , C can be made thinner, and a perpendicular magnetic recording medium having better thermal stability than a conventional crystalline medium can be manufactured.

[Embodiment 2] Unlike Embodiment 1, Embodiment 2 uses an FePt alloy film as the second magnetic layer 3 and
The composition of the ePt alloy film was Fe ₅₀ Pt _50, and the ePt alloy film was formed using a composite target in which Pt pellets were arranged on an Fe target. The rest is the same as in the first embodiment, and the details are omitted here.

Table 3 shows the saturation magnetization Ms, coercive force Hc, perpendicular magnetic anisotropy energy K⊥, and fluctuation field Hf of the PrTbCo single-layer film magnetic recording medium and the PrTbCo / FePt laminated film magnetic recording medium. For comparison, the respective characteristics of the conventional CoCrPt film magnetic recording medium are also shown in the table.

[0033]

[Table 3] As a result, the FeT between the PrTbCo alloy film and the protective film
It can be seen that the deterioration of the magnetic characteristics due to the lamination of the FePt alloy film is small also in the laminated film in which the Pt alloy film is inserted, as in Example 1.

Also, the value of KuV / kT is about 2
A very large value of 500 was obtained, and PrTbCo /
It can be seen that the thermal stability of the FePt laminated film is very excellent.

Next, Table 4 shows the dependency of the corrosion resistance of the magnetic recording medium of the PrTbCo / FePt laminated film and the magnetic recording medium of the PrTbCo single layer film on the thickness of the protective film. The corrosion resistance was examined in the same manner as in Example 1. For comparison, the respective characteristics of the conventional CoCrPt film magnetic recording medium are also shown in the table.

[0036]

[Table 4] Thus, in the case of the PrTbCo / FePt laminated magnetic recording medium, no pitting was observed when the thickness of the C film was 100 ° or more. The number and magnitude of pitting corrosion was very low. In the case of the conventional CoCrPt film, no pitting was observed when the C film thickness was 100 ° or more.

From the above results, by inserting the FePt-based perpendicular magnetization film between the PrTbCo amorphous alloy film and the C protective film, compared with the case of a single PrTbCo film,
The thickness of the C protective film can be reduced without lowering the corrosion resistance, and a perpendicular magnetic recording medium having better thermal stability than a conventional crystalline medium can be manufactured.

The feature of the present invention is that when a rare earth-transition metal amorphous film, which is considered to have better thermal stability than a conventional medium, is used for a magnetic recording medium, a conventional Co-based or FePt-based film is used. An object of the present invention is to make it possible to reduce the thickness of the C protective film without lowering the corrosion resistance by inserting the perpendicular magnetization film between the protective film and the protective film.

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, as the first magnetic layer, the Pr
The present invention is not limited to the TbCo 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.

The second magnetic layer is not limited to the CoCrPt alloy film or the FePt alloy film described in the above embodiment, but may be a conventional Co-based or FePt-based film containing Co and Fe as main components. Similar effects can be obtained when a perpendicular magnetization film is used.

In each of the above embodiments, the C film is used as the protective film 14, but it is clear that other inorganic materials such as Ta and alumina can be used.

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 and the first magnetic layer.

In each of the above embodiments, the substrate 1
Although a glass substrate was used as 1, other substrates such as aluminum alloys, ceramics, and plastics, or substrates that have been subjected to a surface treatment can also 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 a perpendicular magnetic recording medium,
A medium in which a third magnetic layer is formed between the substrate and the first magnetic layer, and the first and second magnetic layers serving as recording layers are sandwiched between the magnetic head and the third magnetic layer, is considered. The third magnetic layer includes a Ni—Fe alloy film, a Co—Fe alloy film, a Fe—
An Al-Si alloy film, a Co-Zr-Nb alloy film, or the like can be 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. When a single pole head is used for recording, the third magnetic layer plays the role of the second pole and forms a magnetic path for circulating magnetic flux. Therefore, when a single-pole head is used, the leakage of the magnetic field in the track width direction is reduced and the track pitch can be narrowed as compared with the case where a ring-type magnetic head is used.

[0046]

As described above, according to the present invention, a rare earth-transition metal amorphous film can be used for a perpendicular magnetic recording medium without deteriorating the corrosion resistance. In comparison, it is possible to provide a perpendicular magnetic recording medium that is more resistant to thermal disturbance and capable of increasing the density.

[Brief description of the drawings]

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

[Explanation of symbols]

 Reference Signs List 1 substrate 2 first magnetic layer 3 second magnetic layer 4 protective film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Hidekazu Hayashi 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Souji 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F-term (for reference) 5D006 BB01 BB05 BB07 BB08 DA03 EA03 FA01 FA09 5E049 AA01 AA04 AC01 AC05 BA06 BA12 CB01 CC01 DB04 GC01

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic layer and a protective film are sequentially laminated on a substrate, wherein the magnetic layer comprises a first magnetic layer and a second magnetic layer from the substrate side, Is an amorphous alloy having perpendicular magnetic anisotropy and comprising a light rare earth, a heavy rare earth and a 3d transition metal. 2. The magnetic recording medium according to claim 1, wherein the second magnetic layer is a perpendicular magnetization film containing Co or Fe.