JP2002092843A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that when only a granular soft magnetic film is used as a soft magnetic bed film in order to increase recording density of a perpendicular magnetic recording medium, magnetic domain walls are generated, thereby noise is generated due to shift and fluctuation of the magnetic domain walls to exert adverse influence on a recording pattern on an magnetic film of an upper layer and consequently a magnetic recording medium by which the adverse influence is eliminated and high density recording with low noise is enabled, is necessary. SOLUTION: The perpendicular magnetic recording medium has a substrate, at least one layer or above of bed film on the substrate and a magnetic film on the bed film. Further the soft magnetic bed film provided on the substrate has two-layer complex structure composed of an upper layer having granular structure in which soft magnetic metallic particles are dispersed in a nonmagnetic base material and a lower layer having continuous film structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium such as a magnetic disk and, more particularly, to a perpendicular magnetic recording medium having good recording and reproducing characteristics.

[0002]

2. Description of the Related Art In recent years, as personal computers and workstations have become more sophisticated and smaller, magnetic disk devices as hard disk drives have also become smaller and larger in capacity. The magnetic disk employed in this magnetic disk device is required to have a higher areal recording density, and a perpendicular magnetic recording method is being studied to realize this.

In the perpendicular magnetic recording system, a magnetic layer for magnetic recording (perpendicular magnetic film) has an axis of easy magnetization in a direction perpendicular to the running direction of a magnetic tape, a magnetic disk or the like, that is, in a thickness direction of a magnetic recording medium. Use a perpendicular magnetic recording medium provided on the surface. Using a perpendicular magnetic recording head that produces a strong magnetization distribution in the thickness direction of the perpendicular magnetic recording medium, the perpendicular magnetization film of the magnetic recording medium is magnetized in the thickness direction of the medium, and information is recorded by leaving the magnetization. Things.

In addition, a soft magnetic film having a high magnetic permeability is provided as a base film on a substrate as compared with a perpendicular magnetic recording medium having only a single layer of perpendicular magnetic film on a substrate as a magnetic recording medium, and a perpendicular magnetic film is further formed thereon. It is known that a perpendicular magnetic recording medium having a two-layer structure in which a film is formed exhibits better recording / reproducing characteristics due to an interaction between a magnetic head and a base film formed of a soft magnetic film (for example, JP-A-52-78403). Therefore, in the case of a perpendicular magnetic recording medium, a method of providing a soft magnetic underlayer (backing film) under a perpendicular magnetization film has been widely studied.

[0005]

Conventionally, however, it is preferable that the soft magnetic underlayer has a high magnetic permeability and a high saturation magnetic flux density. However, recording is performed using the above-described conventional two-layered perpendicular magnetic recording medium. When a reproduction experiment is performed, spike noise is observed. It is known that this spike noise is not observed in a perpendicular magnetic recording medium having a single-layer structure composed of only a perpendicular magnetization film. This noise is caused by the soft magnetic underlayer and
It is not caused by the interaction with the perpendicular magnetic film thereon, but is caused by the soft magnetic film. Also, it is known that this noise is not generated uniformly in the medium, but is generated in a portion where a domain wall exists, and is not generated in a portion without a domain wall (Japanese Patent Publication No. 3-53686). . This noise is called Barkhausen noise, and is caused by irreversible domain wall movement.

In order to suppress the generation of Barkhausen noise, a structure may be adopted in which domain wall motion in a soft magnetic film which is a base film of a perpendicular magnetization film is suppressed or domain walls are completely eliminated.

In order to eliminate the domain wall structure, a perpendicular magnetic recording medium having a granular structure using fine particles of Co or CoPt as a soft magnetic film has been considered. As a magnetic material in the film having such a granular structure, it is conceivable that hard magnetic particles such as Co and CoPt having a high Hk have a particle size close to a very small superparamagnetic particle. In this case, it seems at first glance that it is possible to show the behavior as soft magnetic particles near room temperature.However, when such a granular film is used as a base film, when recording a signal, it is difficult to record a signal with the hard layer. Similarly, H at high-speed magnetization reversal
c, that is, Dynamic coercity;
It has been found that Hc0 is significantly different from Hc in normal measurement.

[0008] Essentially, microparticles, which are hard magnetic materials, act as a hard film at the time of recording and cannot form a domain wall. However, they hardly affect the recording process of the magnetic film as a hard film. It has been found that the recording pattern is affected at the recording stage before a disturbance due to a recording transition domain wall, an external magnetic field, or the like, and a fine bit pattern cannot be formed.

Therefore, in the case of a base film having a granular structure, it is necessary that Hk of the magnetic film be small, and by covering the uppermost layer of the base film with the base material in the granular base film, the surface smoothness is improved. It has become possible to create magnetic films.

[0010] However, although the influence of noise can be reduced by making the underlayer film, which is a soft magnetic film, a granular structure, the magnetic film is diluted with a non-magnetic base material, and compared with a continuous film. Then the average Bs as a film
The problem that the size becomes smaller has also become apparent.

Therefore, in the present invention, Hk in the non-magnetic base material is
By providing a continuous film of soft magnetic particles further below the granular film, which is a soft magnetic underlayer having a structure in which small soft magnetic fine particles are dispersed, it serves as a yoke when a recording magnetic field is generated together with a perpendicular recording head. It is possible to supplement the role of the soft magnetic layer.

Further, by forming the soft magnetic underlayer into a composite structure of a granular film as the upper layer and a continuous film as the lower layer, the magnetic flux emitted from the main pole of the head is applied to the magnetic particle portion having a high magnetic permeability in the upper granular film. And returns to the return pole of the head without passing through the non-magnetic base material in the intergranular portion and passing through the lower continuous magnetic film, so that it is possible to obtain a head magnetic field concentration effect on the surface of the soft magnetic film. .

As described above, in the present invention, it is preferable that the soft magnetic underlayer has a high magnetic permeability and a high Bs. It is an object of the present invention to provide a magnetic recording medium capable of performing high-density recording with low noise by eliminating adverse effects (demagnetization, overwriting, etc.) on a recording pattern of a film.

[0014]

In order to achieve the above object, a perpendicular magnetic recording medium according to the present invention has a substrate and at least one underlayer on the substrate. In a magnetic recording medium having a magnetic film thereon, a soft magnetic underlayer provided on the substrate, and the soft magnetic underlayer has an upper layer having a granular structure in which soft magnetic metal particles are dispersed in a nonmagnetic matrix. And a lower layer having a continuous film structure.

With such a structure, the soft magnetic underlayer has a granular structure with no magnetic domain walls, so that the noise can be reduced. In addition, the fact that the effective Bs is diluted and reduced by the non-magnetic base material reduces the noise. This can be compensated for by providing a continuous soft magnetic film to such an extent that there is no effect.

[0016]

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

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

The perpendicular magnetic recording medium 1 has a laminated structure composed of a substrate 2, a soft magnetic underlayer 3, a perpendicular magnetization film 4, and a protective film 5 on the substrate 2 in that order.

As the substrate 2, glass, aluminum,
Silicon, plastic, synthetic resin, or the like can be used. The shape of the substrate 2 may be any of a disk, a tape, and a drum. The soft magnetic underlayer 3 and the perpendicular magnetization film 4 constituting the perpendicular recording medium 1 of the present invention can be formed by a physical vapor deposition method such as a sputtering method, a vacuum deposition method, a gas sputtering method, and a gas flow sputtering method. Perpendicular magnetization film 4
Is a ferromagnetic material containing at least one element selected from Co, Fe and Ni, for example, CoPtCr, CoCrTa, CoTaP
t, CoNiTa, CoPt and the like. The soft magnetic underlayer 3 has a two-layer structure of an upper layer portion 3a having a granular structure in which a soft magnetic material is dispersed in a non-magnetic base material, and a lower layer 3b having a continuous structure of the soft magnetic material.

Upper layer 3a, lower layer 3b of soft magnetic underlayer 3
The soft magnetic material constituting at least Co, Fe,
Soft magnetic material containing at least one element selected from Ni, for example, CoFe, NiFe, CoZnNb
Are used. The non-magnetic base material of the upper layer portion 3a includes:
Nonmagnetic metals such as Ag, Ti, Ru, C and their compounds, or oxides, nitrides, fluorides, carbides, for example, Si
O2, SiO, Si3N4, Al2O3, AlN, Ti
N, BN, CaF, TiC, etc. are used.

In particular, when a material which also has a role of controlling the crystallinity and orientation of the perpendicular magnetization film 4 such as Ti, TiN is used as the base material, the soft magnetic under film 3, the perpendicular magnetization film 4, The spacing between the recording head magnetic pole and the soft magnetic underlayer 3 is reduced, the efficiency of the soft magnetic underlayer 3 is increased, and higher density recording is possible. It is also possible to provide an intermediate layer between the soft magnetic underlayer 3 and the perpendicular magnetization film 4 for controlling the crystallinity and orientation of the perpendicular magnetization film 4 such as Ti, non-magnetic CoCr, or the like.

Next, three types of magnetic recording media A to C were prepared as described below, and each magnetic recording medium was evaluated.

(Sample A) The substrate 2 is 2.5 inch glass, and the soft magnetic underlayer 3 is CoFe as a soft magnetic material.
Using a TiN target as a target and a nonmagnetic base material, Co80Fe20 is used as a continuous soft magnetic film 3b formed as a lower layer of the soft magnetic underlayer 3, and C is used as a granular soft magnetic film 3a formed as an upper layer of the soft magnetic underlayer 3.
The volume composition ratio after film formation of o80Fe20 and TiN is 60:
Using a composite target adjusted to be 40, a film was formed by a facing stationary magnetron sputtering method.

More specifically, a 100% Co80Fe20 target is formed on the glass substrate 2 in an Ar gas atmosphere.
A continuous soft magnetic film 3b having a thickness of 100 nm was formed, and subsequently, a granular soft magnetic film 3a was formed to have a thickness of 100 nm. Using a CoPt20Cr16 alloy target as the perpendicular magnetization film 4 continuously, a perpendicular magnetization film 4 of CoPt20Cr was formed to 50 nm in a mixed gas obtained by adding a small amount of oxygen to Ar gas, and finally, a C protective film was formed to 8 nm. Filmed.

Next, a plurality of perpendicular magnetic recording media 1 as described below were prepared, and their magnetic properties and film structures were compared and studied.

The magnetic properties of the formed film are VSM (Vibr
atting Sample Magnetometer
r), the film structure is TEM (Transmission)
(Electron Spectroscopy).

On the substrate 2, only the granular soft magnetic layer 3a according to the first embodiment is provided by 10, 50, 100,
A perpendicular magnetic recording medium 1 having a thickness of 200, 400, and 600 nm, and a perpendicular magnetic recording medium having a continuous soft magnetic film 3b formed between the granular soft magnetic film 3a and the substrate 2, that is, under the granular soft magnetic film 3a. The noise of the recording medium 1 was measured.

FIG. 3 shows the relationship between the thickness of the soft magnetic underlayer 3 when the saturation magnetization of the entire soft magnetic underlayer 3 of each medium is Ms, and the soft magnetic underlayer when the DC noise is Ndc. FIG. 4 shows the result of measuring the relationship between the film thickness of No. 3 and the film thickness.

The noise of the perpendicular magnetic recording medium 1 using only the granular soft magnetic film 3a was very small and slightly increased with the film thickness. On the other hand, the perpendicular magnetic recording medium 1 in which the continuous soft magnetic film 3b is formed under the granular soft magnetic film 3a.
In the above, the thickness of the granular soft magnetic film 3a is 10 n
m, the noise was about twice as large as that of the perpendicular magnetic recording medium 1 using only the granular soft magnetic film 3a.
At 0 nm or more, the noise level was about the same as that of the perpendicular magnetic recording medium 1 using only the granular soft magnetic film 3a.

This is because the influence of the noise caused by the continuous soft magnetic film 3b formed under the granular soft magnetic film 3a greatly appears. When the granular soft magnetic film 3a is thin, the continuous soft magnetic It is considered that the noise of the film 3b may have leaked to the surface of the granular soft magnetic film 3a formed thereon. When the granular soft magnetic film 3a becomes thick to some extent, it is considered that the influence of the above-mentioned leakage can be ignored.

It is considered that this film thickness is determined by Bs and magnetic permeability of the soft magnetic underlayer 3, the film thickness of the granular soft magnetic film 3a, the volume content of magnetic particles in the granular soft magnetic film 3a, and the like.

Next, noise characteristics of the perpendicular magnetic recording medium 1 in which the perpendicular magnetization film 4 was formed on the soft magnetic underlayer 3 in which the above-described granular soft magnetic film 3a and continuous soft magnetic film 3b were combined were examined. For the measurement, a GMR head having a read gap length of 0.5 μm and a read track width of 0.8 μm, and a main pole film thickness of 0.
The measurement was performed using a single pole head having a recording track width of 2 μm and a flying height of 40 nm using a spin stand. S when recording at a recording density of 250 Kfci
0 / NmRMS was measured.

Next, S0 / N of the above-described perpendicular recording medium 1
The result of measuring the resolution obtained by differentiating m will be described with reference to FIG.

S0 / Nm of perpendicular magnetic recording medium 1 described above
Was measured to determine the resolution PW50,
In the following, the PW50 is poor because the effect of the noise of the continuous soft magnetic film 3b is large, but for 100 nm or more, the perpendicular magnetic recording medium 1 using the soft magnetic underlayer 3 in which the granular soft magnetic film 3a and the continuous soft magnetic film 3b are combined. It was found that the PW50 was smaller than that of the perpendicular magnetic recording medium 1 using only the granular soft magnetic film 3a as the soft magnetic underlayer 3.

In the perpendicular magnetic recording medium 1 described above, a granular soft magnetic film 3a of the soft magnetic underlayer 3 was formed by RF sputtering using a composite target in which the nonmagnetic base material was SiO2. As a result of measuring the magnetic characteristics of the perpendicular magnetic recording medium 1, the noise in the low range, and the PW50, there was almost no difference from the case where TiN was used as the base material. However, in the high frequency range of 500 Kfci or more, the perpendicular magnetic recording medium 1 using TiN as a base material shows an increase in noise and PW50, and the perpendicular magnetic recording medium 1 using SiO2 as a base material has a high Both noise and PW50 were good.

The overwrite characteristic when high-frequency recording was performed was about 20 dB in the perpendicular magnetic recording medium 1 using TiN as a base material, whereas the perpendicular magnetic recording medium using SiO2 as a base material was about 20 dB. 1 shows a value of about 30 dB, an eddy current is generated at a high frequency, and a low-resistance T
It was found that recording was insufficient with the perpendicular magnetic recording medium 1 using iN as a base material. On the other hand, high resistance S
It is considered that the perpendicular magnetic recording medium 1 using iO2 as a base material was able to record sufficiently because generation of eddy current was suppressed.

[0037]

As described above in detail, according to the present invention, the influence of noise can be reduced to some extent by the perpendicular magnetic recording medium using only the granular soft magnetic film as the soft magnetic underlayer. Since the magnetic film was diluted with a non-magnetic base material, the average Bs of the film was smaller than that of the continuous film. By forming the soft magnetic underlayer into a two-layer structure of a granular soft magnetic film (upper layer) and a continuous soft magnetic film (lower layer), the lower continuous soft magnetic film complements the role of the soft magnetic underlayer as a yoke. In this way, the above problems could be solved.

Further, by forming a composite structure of a granular soft magnetic film as the upper layer of the soft magnetic underlayer and a continuous soft magnetic film as the lower layer, it is possible to obtain a magnetic field concentration effect on the surface of the soft magnetic underlayer. The magnetic flux emitted from the main magnetic pole of the perpendicular magnetic head concentrates on the magnetic particles having high magnetic permeability in the upper granular soft magnetic film, and does not pass through the non-magnetic base material in the portion between the particles.
The light passes through the lower continuous soft magnetic film and returns to the return pole of the perpendicular magnetic head, so that it is possible to provide a magnetic recording medium with low noise and capable of high-density recording.

[Brief description of the drawings]

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

FIG. 2 is an enlarged schematic view and a front view of a section A of FIG. 1;

FIG. 3 is a diagram for explaining the relationship between the saturation magnetization Ms and the thickness of a granular underlayer in the perpendicular magnetic recording media of the present embodiment and a conventional example.

FIG. 4 is a view for explaining the relationship between the state of noise generation and the thickness of a granular base film in the perpendicular magnetic recording media of the present embodiment and a conventional example.

FIG. 5 is a view for explaining the relationship between the PW50 and the thickness of a granular base film in the perpendicular magnetic recording media of the present embodiment and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Perpendicular magnetic recording medium 2 ... Substrate 3 ... Soft magnetic underlayer 3a ... Granular soft magnetic film (upper layer) 3b ... Continuous soft magnetic film (lower layer) 4 ... Perpendicular magnetization film 5 ... …… Protective film 6 …… Soft magnetic particles

Claims (5)

[Claims] 1. A magnetic recording medium having a substrate, at least one underlayer on the substrate, and a magnetic film on the underlayer, comprising: a soft magnetic underlayer provided on the substrate; The magnetic recording medium according to claim 1, wherein the soft magnetic underlayer comprises an upper layer having a granular structure in which soft magnetic metal particles are dispersed in a nonmagnetic base material, and a lower layer having a continuous film structure. 2. The magnetic recording medium according to claim 1, wherein the magnetic flux density of the upper granular soft magnetic film forming the soft magnetic underlayer is equal to or larger than the saturation magnetic flux density of the lower continuous film. 3. The soft magnetic metal film according to claim 1, wherein the volume content of the soft magnetic metal particles in the upper granular soft magnetic film forming the soft magnetic underlayer is 4%.
2. The magnetic recording medium according to claim 1, wherein the content is 0% or more and 87% or less. 4. The magnetic recording medium according to claim 1, wherein the soft magnetic metal particles in the upper granular soft magnetic film forming the soft magnetic underlayer have a particle size of 5 nm or more and 40 nm or less. 5. The magnetic recording medium according to claim 1, wherein a high electric resistance material is used as a non-matrix material of the upper granular soft magnetic film forming the soft magnetic underlayer.