JPH1040528A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which can improve quality of reproduced signals and decrease an error rate. SOLUTION: In a magnetic recording medium having a magnetic film 2 formed of magnetic particles 3 and a non-magnetic grain boundary 4 on a substrate 1, when the magnetic film 2 has a thickness (t), a residual magnetization moment is Ir, an average particle size of the magnetic particles 3 in an in-plane direction of the magnetic film 2 is (d) and an activation magnetic moment of the magnetic film 2 is v*Isb, a condition of d<2> *t*Ir/(v*Isb)>=0.75, preferably, d<2> *t*Ir/(v*Isb)>1.5 is satisfied.

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 mainly used for a hard disk drive and a method for manufacturing the same.

[0002]

2. Description of the Related Art A magnetic disk device, particularly a hard disk device using a magnetic recording medium in which a magnetic film is formed on a rigid disk-shaped substrate, is characterized by its high recording density, high speed, rewritable, and low bit cost. It is widely used as an external storage device of computer equipment such as a computer, a large-sized computer, and a word processor, and further improvement in recording density is expected for large capacity. To increase the recording density, the magnetic recording medium must have a high coercive force of the magnetic film to improve the linear recording resolution.
In order to prevent a reproduction error from occurring, it is required to reduce noise included in a reproduction output to improve reproduction signal quality.

[0003] The noise included in the reproduction output from the magnetic recording medium is related to the structure of the magnetic film of the medium, and is generated when the magnetic interaction between the magnetic particles of the ferromagnetic material constituting the magnetic film is strong. Is known to grow. Therefore, in order to reduce the noise and improve the quality of the reproduced signal, various measures have been taken to reduce the magnetic interaction between the magnetic particles.

The first is to increase the concentration of Cr added to the magnetic film so as to make the grain boundaries non-magnetic, and the second is to segregate oxygen to the grain boundaries under the conditions for forming the magnetic film. The third method is to reduce the magnetic interaction by dispersing magnetic particles in a non-magnetic base material. Further, since the addition of Cr lowers the saturation magnetization of the magnetic particles, it is considered that there is also an effect of reducing the magnetostatic interaction between the magnetic particles.

[0005] In particular, the second and third methods are advantageous in that a high coercive force can be achieved without reducing the crystal magnetic anisotropy, and can cope with a high recording density. Further, it is also known that the activation magnetic moment v * Isb corresponding to the amount of magnetization of magnetically separated magnetic particles has a correlation with the amount of noise. As a method of controlling v * Isb to reduce the amount of noise, thinning of a magnetic film has been attempted. However, as a result of the study by the inventors, when an error rate was measured by combining such a medium having a thin magnetic film with a head, the error rate was not improved. It is considered that the thinning of the magnetic film caused a decrease in the intensity of the reproduction signal, and did not lead to an improvement in the quality of the reproduction signal.

When the amount of Cr added is increased, v
* Isb was reduced, but the reproduced signal strength was also reduced and the reproduced signal quality was reduced. As a result, the error rate was not improved.

[0007]

As described above, as described above, although it is possible to reduce the noise included in the reproduction output with the conventional technology, the reproduction signal intensity also decreases with the reduction of the noise. Therefore, there is a problem that the error rate cannot be effectively improved by improving the reproduction signal quality.

The present invention has been made to solve the above problems, and has as its object to provide a magnetic recording medium capable of improving the quality of a reproduced signal and reducing an error rate, and a method of manufacturing the same.

[0009]

According to the present invention, there is provided a magnetic recording medium comprising a magnetic film comprising magnetic particles and non-magnetic grain boundaries formed on a substrate. When the residual magnetization moment is Ir, the average particle diameter of the magnetic particles in the in-plane direction of the magnetic film is d, and the activation magnetic moment of the magnetic film is v * Isb, d ² * t * Ir / (v * Isb) ) ≧ 0.75 (1) Preferably, d ² * t * Ir / (v * Isb)> 1.5 (2)

In the magnetic recording medium configured as described above,
By satisfying the expression (1), the magnetic interaction between the magnetic particles decreases in the thickness direction of the magnetic film.
Is satisfied, the magnetic separation in the thickness direction of the magnetic particles is more effectively performed, so that the particle size of the magnetic particles and the film thickness of the magnetic film are not reduced unnecessarily, that is, the reproduction signal intensity is reduced. The noise amount is reduced without any noise. As a result, the quality of the reproduced signal is improved, and the error rate can be reduced.

Further, in the magnetic recording medium of the present invention, (1)
As shown in (2), the direction is to increase t * Ir, and increasing t * Ir has conventionally been considered unfavorable because the recording resolution is lowered. It is considered that the improvement in S / Nm makes it possible to compensate for the decrease in the recording resolution, which can lead to an improvement in the error rate.

The magnetic film according to the present invention may have a structure in which magnetic particles are dispersed in a non-magnetic base material forming a non-magnetic grain boundary, or oxygen or Cr segregates in the non-magnetic grain boundary. It may have a structure.

Further, when the magnetic recording medium according to the present invention is formed by sputtering under optimal conditions using a target composed of a non-magnetic base material and magnetic particles, for example, the magnetic recording medium may be subjected to optimal conditions in an atmosphere containing a Co alloy. In the case where a magnetic film composed of magnetic particles and non-magnetic grain boundaries is formed on a substrate by sputtering, it can be realized by dividing the sputtering into a plurality of times.

[0014]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view of a magnetic recording medium according to an embodiment of the present invention, and FIG. 2 is a view showing a planar TEM image of a magnetic film. This magnetic recording medium is formed by forming a magnetic film 2 on a rigid disk-shaped substrate 1, and the magnetic film 2 has a structure in which magnetic particles 3 are separated by nonmagnetic grain boundaries 4.

Here, based on the present invention, the magnetic particles 3 are magnetically separated from each other in the in-plane direction of the magnetic film as shown in FIG. Separated.

When the thickness of the magnetic film 2 is t, the residual magnetization moment is Ir, the average particle diameter of the magnetic particles 3 in the in-plane direction is d, and the activation magnetic moment of the magnetic film 2 is v * Isb.
The magnetic film 2 is configured to satisfy the condition of d ² * t * Ir / (v * Isb) ≧ 0.75 (1), and more preferably, d ² * t * Ir / (v * Isb)> 1. 5 It is configured to satisfy the condition of (2).

Here, the particle diameter d is an average value of 200 diameters obtained from the planar TEM (transmission electron microscope) image of the magnetic film 2 shown in FIG. The unit is (nm). Further, t * Ir is a value measured by a VSM (vibrating sample magnetometer), and its unit is (nm * T). Further, the activation magnetic moment v
* Isb is obtained by VSM from the time dependency of the coercive force Hc of the magnetic film 2 as shown in FIG. 3 as v * Isb = kT / {ΔHc / Δln (t)}, and the unit thereof is (nm) ³ * T).

With this configuration, in the magnetic recording medium of the present invention, the noise can be reduced without lowering the reproduction signal strength, the reproduction signal quality can be improved, and the error rate during reproduction can be reduced. be able to. This effect will be described qualitatively as follows.

[0019] magnetic particles in the magnetic layer is assumed to form a magnetically continuous cylindrical in the direction of film thickness of the magnetic film, the volume of the magnetic particles from a ^{(πd 2/4) * t} , one the total magnetization per particle is approximately ^{(πd 2/4) * t} * is given by Ir, which activates the magnetic moment of the magnetic film v * is
equal to b. ^{That, (πd 2/4) *} t * Ir = v * Isb (3) In addition, π / 4 = 0.785 from the equation (3) is ^{d 2 * t * Ir / v} * Isb = 0.785 (4 ).

Here, to make d ² * t * Ir / v * Isb larger than, for example, 0.785 means that cylindrical magnetic particles long in the thickness direction of the magnetic film are magnetically separated in the thickness direction. Corresponding to weakening their magnetic interaction.
That is, as d ² * t * Ir / v * Isb is increased, the magnetic interaction between the magnetic particles in the thickness direction of the magnetic film becomes smaller, and the noise is reduced.
At this time, the positions in the film thickness direction that are magnetically separated may be different at locations within the film surface. Further, magnetic separation can be achieved by a difference in orientation as long as magnetic particles have a large anisotropy even when there is no nonmagnetic layer.

Therefore, unlike the conventional method of reducing the particle size and the thickness of the magnetic film, it is possible to reduce the noise without lowering the intensity of the reproduced signal and to improve the quality of the reproduced signal. Can be reduced.

According to experiments by the inventors, when d ² * t * Ir / (v * Isb) ≧ 0.75 is satisfied, a low error rate of e- ⁵ or less, which can sufficiently cope with error correction, is obtained. If d ² * t * Ir / (v * Isb)> 1.5 belongs to a film, it is possible to realize a lower error rate of e- ¹¹ or less that can withstand practical use without performing error correction. Was confirmed.

Hereinafter, a specific embodiment will be described. (Example 1) As a substrate 1, a glass substrate on which a base film made of a Cr film is formed in advance is prepared, and CoPt magnetic particles are deposited on this glass substrate in a SiO ₂ matrix at a volume ratio of 50%.
%, A CoPt—SiO ₂ film was formed as a magnetic film 2 by DC sputtering while applying an RF bias, thereby producing a magnetic recording medium as shown in FIGS. The CoPt-SiO ₂ film is made of SiO ₂
The structure of the granular film in which CoPt magnetic particles were dispersed in a base material composed of Further, a CoPt-SiO ₂ film was formed by changing the sputtering time variously.

With respect to the CoPt—SiO ₂ film thus formed, the magnetostatic property and the activation magnetic moment were measured. In addition, TE in the in-plane direction of the CoPt—SiO ₂ film
M observation was performed to measure the size of the magnetic particles (crystal grains). The crystal grains were separated at grain boundaries mainly composed of SiO ₂ .

Next, information is written on the magnetic recording medium manufactured in this manner with a high Bs (saturated magnetic flux density) head.
The written information is reproduced by an MR head (magnetoresistive head) having a shield interval of 0.2 μm and a reproduction track width of 1.8 μm, and a signal-to-noise ratio (So / Nm) of the medium is obtained.
) And the error rate was evaluated by data reproduction using maximum likelihood decoding. Table 1 shows the results.

[0026]

[Table 1]

Table 1 shows t * Ir (nm * T), v * Is
b (nm ³ * T), d and d ² * t * Ir / (v * I
The results of measurement of So / Nm and error rate of Samples 1 to 11 in which the combination of sb) was variously changed are shown. From this result, v * Isb is CoPt-Si
It can be seen that it changes depending on the thickness t of the O ₂ film. Also, So / Nm, that is, the noise amount changes corresponding to v * Isb. But for the error rate,
No correlation with v * Isb has been obtained.

From Table 1, when the condition of d ² * t * Ir / (v * Isb) ≧ 0.75 is satisfied (samples 1 to 5), a low error rate of e- ⁵ or less was obtained. With such an error rate, the error rate can be sufficiently corrected by the error correction of the reproducing system.

In particular, when the condition of d ² * t * Ir / (v * Isb)> 1.5 is satisfied (sample 1), a lower error rate of e- ¹¹ or less can be realized and error correction can be performed. It can be unnecessary.

On the other hand, using a CoCrPtTa target as a comparative example,
A magnetic recording medium was fabricated by forming a CrPtTa / Cr film on a Si substrate. For these CoCrPtTa / Cr films, the magnetostatic properties and the activation magnetic moment were measured, and the size of the magnetic particles was measured by performing TEM observation in the plane direction of the film. As a result, d ² * t * Ir / (v *) A film satisfying the condition of Isb) ≧ 0.75 was not obtained.

When information was written to the magnetic recording medium, reproduced by the MR head, and the error rate was evaluated, the error rate was e- ⁴ or more, which was large enough to make error correction difficult or impossible. It was confirmed that it was too large to be practically used.

FIG. 4 shows the relationship between d ² * t * Ir / (v * Isb) and the error rate of the magnetic recording medium manufactured by the method of the first embodiment. As can be seen from the figure, d ² * t * I
By setting r / (v * Isb) ≧ 0.75, a low error rate of e- ⁵ or less can be obtained, and d ² * t * Ir
It can be seen that by setting /(v*Isb)>1.5, a lower error rate of e- ¹¹ or less can be realized.

FIG. 5 is a graph showing the magnetic characteristics, that is, the relationship between the coercive force Hc and Ir * t. (Example 2) As a substrate 1, a glass substrate on which a base film made of a V film is formed is prepared.
Using an oPtCr target, a CoPtCrO / V film was formed by DC sputtering in an Ar atmosphere containing oxygen. At this time, magnetic recording media were manufactured in which the film thickness was variously changed by changing the sputtering time.

With respect to the CoPtCrO / V film thus formed, the magnetostatic property and the activation magnetic moment were measured. In addition, TE in the in-plane direction of the CoPtCrO / V film
M observation was performed to measure the size of the magnetic particles (crystal grains). The CoPtCrO / V film was amorphous, and the magnetic particles were separated by grain boundaries where Cr or oxygen segregated.

Next, as in the first embodiment, information is written on the magnetic recording medium thus manufactured with a high Bs head.
The written information is reproduced by an MR head having a shield interval of 0.2 μm and a reproduction track width of 1.8 μm, measuring a signal-to-noise ratio (So / Nm) of the medium, and an error rate by data reproduction using maximum likelihood decoding. Was evaluated. Table 2 shows the results.

[0036]

[Table 2]

Table 2 shows that t * Ir (nm *
T), v * Isb (nm ³ * T), d and d ² * t *
The results of measuring So / Nm and the error rate of Samples 12 to 16 in which the combination of Ir / (v * Isb) was variously changed are shown. From this result, v * Isb
Is changed depending on the thickness t of the CoPtCrO / V film. Also, So / Nm, that is, the amount of noise,
It changes corresponding to v * Isb. However, the error rate has not been correlated with v * Isb.

From Table 2, when the condition of d ² * t * Ir / (v * Isb) ≧ 0.75 is satisfied (samples 12 to 14), a low error rate of e- ⁵ or less is obtained, and the reproduction is performed. It can be seen that the system can be practically used by error correction.

Example 3 As a substrate 1 of FIG. 1, a glass substrate on which a base film made of a V film was formed was prepared, and a CoPtCr target was used on this glass substrate in an Ar atmosphere containing oxygen. CoPtC by DC sputtering
An rO / V film was formed. At this time, in this embodiment, a CoPtCrO / V film was formed by providing a pause time during the entire sputtering time, that is, by dividing the sputtering into a plurality of times.

The magnetostatic properties and the activation magnetic moment of the CoPtCrO / V film thus formed were measured. In addition, TE in the in-plane direction of the CoPtCrO / V film
M observation was performed to measure the size of the magnetic particles (crystal grains).

Next, as in Examples 1 and 2, information was written on the manufactured magnetic recording medium with a high Bs head, and this information was written with a shield interval of 0.2 μm and a read track width of 1.8 μm.
The signal was reproduced by the m MR head, the signal-to-noise ratio (So / Nm) of the medium was measured, and the error rate was evaluated by data reproduction using maximum likelihood decoding. Table 3 shows the results.

[0042]

[Table 3]

Table 3 shows that, similarly to Tables 1 and 2, t * Ir
(Nm * T), v * Isb (nm ³ * T), d and d
² shows the results of measurement of So / Nm and error rate for samples 17 and 18 in which the combination of ² * t * Ir / (v * Isb) was variously changed. From these results, both samples 17 and 18 can satisfy the condition of d ² * t * Ir / (v * Isb)> 1.5, realize a lower error rate of e− ¹¹ or less, and be practical without error correction. It was confirmed that it could be provided.

[0044]

As described above, according to the magnetic recording medium of the present invention, the reproduction signal intensity can be reduced by reducing the magnetic interaction between the magnetic particles of the magnetic film in the thickness direction. Noise can be reduced, the quality of the reproduced signal can be improved, and the error rate can be effectively reduced.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a planar TEM image of the magnetic film according to the embodiment.

FIG. 3 is a diagram showing a method of obtaining v * Isb.

FIG. 4 shows d ² * t * of the magnetic recording medium obtained in Example 1.
The figure which shows the relationship between Ir / (v * Isb) and an error rate.

FIG. 5 is a graph showing a magnetic characteristic graph of the magnetic recording medium obtained in Example 1.

[Description of Signs] 1 ... Substrate 2 ... Magnetic film 3 ... Non-magnetic base material 4 ... Magnetic particles

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsutaro Ichihara, 70, Yanagimachi, Kochi-ku, Kawasaki, Kanagawa Prefecture Inside the Toshiba Yanagimachi Plant Co., Ltd. (72) Inventor Tetsu Kikitsu 70, Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture

Claims (5)

[Claims] 1. A magnetic recording medium comprising a magnetic film comprising magnetic particles and non-magnetic grain boundaries formed on a substrate, wherein the thickness of the magnetic film is t, the residual magnetization moment is Ir, and the film surface of the magnetic film is The average particle diameter of the magnetic particles in the inward direction is d, and the activation magnetic moment of the magnetic film is v * Isb.
A magnetic recording medium characterized by satisfying the following condition: d ² * t * Ir / (v * Isb) ≧ 0.75. 2. The thickness of the magnetic film is t, the residual magnetization moment is Ir, the average particle diameter of the magnetic particles in the in-plane direction of the magnetic film is d, and the activation magnetic moment of the magnetic film is v *. A magnetic recording medium characterized by satisfying a condition of d ² * t * Ir / (v * Isb)> 1.5, where Isb. 3. The magnetic recording medium according to claim 1, wherein the magnetic film has a structure in which magnetic particles are dispersed in a non-magnetic base material forming the non-magnetic grain boundaries. 4. The magnetic recording medium according to claim 1, wherein the magnetic film has a structure in which oxygen or Cr is segregated at the nonmagnetic grain boundaries. 5. A method for manufacturing a magnetic recording medium, comprising a step of forming a magnetic film comprising magnetic particles and non-magnetic grain boundaries on a substrate by sputtering, wherein when forming the magnetic film on the substrate, A method of manufacturing a magnetic recording medium, wherein the method is performed by dividing the method into times.