JPH1079307A - Magnetic recording medium and magnetic recording reproduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise and to enhance reproduction output by a method wherein a magnetic thin film has a hexagonal system structure, c-axis is in almost vertical direction to the surface of the thin film or it is inclined to one direction from vertical direction, the Cr density in the grain boundary of the microscopic crystal grain of the magnetic thin film is higher than the average Cr density of the magnetic thin film. SOLUTION: A Ti-Cr alloy film is formed on a disc substrate, consisting of an Al-Mg alloy having a nickel/phosphorus alloy plated film, using a sputtering method, and a magnetic disc is formed by providing a Co-Cr alloy magnetic film and a carbon film as a protective film. The crystal structure of the Co-Cr alloy is hexagonal system, and c-axis is oriented in almost vertical or vertical direction to film surface. The Co density in crystal grain field is higher than the average density of the magnetic thin film and lower than 25 atomic %. The Co-Cr alloy, which is segregated to a grain boundary, has weak spontaneous magnification, a weak replacement interaction works between the adjacent particles, and reproduction output can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium using a ferromagnetic thin film having perpendicular magnetic anisotropy as a recording layer, and has a high signal-to-noise ratio (S / S) even in high-density recording.
N) and a magnetic recording / reproducing apparatus using the same.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable increase in the amount of information handled by information equipment, and there is a strong demand for a dramatic improvement in the storage capacity of magnetic disks, floppy disks, and magnetic tapes used as file media. Under such circumstances, the magnetic recording medium has shifted from a coating type medium using fine magnetic powder to a thin film type medium using a ferromagnetic metal thin film.

[0003] In magnetic recording, information is recorded by reversing the direction of magnetization in a minute region of a ferromagnetic layer serving as a recording medium. At present, as a magnetic recording medium, a so-called longitudinal recording method, in which the direction of magnetization is written in parallel to the medium surface, is widely used. In this recording method, the increase in recording density has been promoted by increasing the coercive force of the medium or reducing the thickness of the magnetic layer. However, the thickness of the longitudinal recording medium is already 40 nm or less even today, and further thinning requires an advanced film forming technique for forming a film having tribological strength and few defects. In addition, from the viewpoint of recording / reproducing characteristics, further thinning causes a decrease in reproduction output and a deterioration of a signal-to-noise ratio, which is a major obstacle to high density.

On the other hand, as a method for solving the above-mentioned disadvantage, a perpendicular recording system in which recording magnetization is magnetized in a direction perpendicular to the medium film surface has been proposed. In this method, a material having strong magnetic anisotropy in the direction perpendicular to the film surface is required, and Co-C
A relatively thick alloy magnetic layer having a thickness of 0.05 to 0.5 μm typified by an r alloy is widely used. The advantage of this recording method is that the higher the recording density, the more stable the recorded magnetization becomes in terms of energy, and is essentially suitable for high-density recording. In addition, unlike the longitudinal recording method, this method has an advantage in manufacturing that it is not necessary to reduce the film thickness or increase the coercive force in order to increase the recording density.

[0005]

The recording medium for perpendicular recording is disclosed in JP-A-57-109127, Journal of the Japan Society of Applied Magnetics, Vol. 9, No. 2, pp. 57-60 (198).
5 years), or IEEE Trans. , MAG-2
4, No. 6, 2706-2708 (1988
It is said that it is preferable to segregate non-magnetic Cr atoms at the grain boundaries of the fine particles constituting the medium, as shown in (1). This is because the corrosion resistance is improved by creating a region with a high Cr concentration on the particle surface, and magnetic separation between particles is caused by segregation of non-magnetic Cr atoms at the grain boundaries as in the case of the longitudinal recording medium. This is because it is considered that the exchange interaction is cut off, the magnetic domain becomes finer, and the medium noise is reduced. Generally, in order to break the exchange interaction, it is desirable that the Cr concentration at the grain boundary be 25 at% or more at which the spontaneous magnetization of the Co—Cr alloy disappears.

However, even if a perpendicular magnetic recording medium is manufactured under the condition that the segregation of Cr atoms has progressed, high reproduction output and recording density characteristics cannot always be obtained.
The advantages of perpendicular recording had not yet been fully exploited.

An object of the present invention is to solve the above-mentioned problems of perpendicular recording, and to provide a perpendicular magnetic recording medium capable of obtaining a high reproduction output with less noise and a magnetic recording / reproducing apparatus using the same.

[0008]

Means for Solving the Problems The inventors of the present invention have repeatedly conducted experiments on the relationship between the magnetic recording / reproducing characteristics of a perpendicular magnetic recording medium and the characteristics of the medium, and as a result, have found that fine crystal grains constituting a Co-Cr alloy have been obtained. The Cr concentration in the field greatly affects the recording / reproducing characteristics, and the optimum Cr concentration is in a lower range than conventionally thought, and the Cr concentration is 21 to 24.
By applying a weak magnetic exchange interaction between adjacent crystal grains as at% or 21 to 25 at%, the reproduction output is greatly improved and the signal-to-noise ratio (S
/ N) is greatly improved, and the present invention has been completed.

That is, the present invention provides a method for producing a Co—C containing Co and Cr as main components directly on a nonmagnetic substrate or via an intermediate layer made of a nonmagnetic metal film or a ferromagnetic metal film.
In a magnetic recording medium provided with an r-based alloy magnetic thin film, the magnetic thin film has a hexagonal crystal structure, and its c-axis is inclined substantially perpendicular to the thin film surface or in one direction from the perpendicular direction. The Cr concentration at the grain boundaries of the microcrystal grains, which are the constituent units of the thin film, is higher than the average Cr concentration of the magnetic thin film.
It is characterized by being lower than 5 at%.

[0010] The Cr concentration at the grain boundary can be in the range of 21 to 24 at%.

A Co—Cr-based magnetic thin film is made of Ta, P
a Co—Cr-based alloy thin film to which at least one element selected from the group consisting of t, Ni, Nd, B, and Si is added;
The combined concentration of Cr and the third element in the grain boundary is 21 to
It can be in the range of 25 at%.

The non-magnetic metal film constituting the intermediate layer is made of T
i, Ge, Cr-Ti alloy, Zn, etc.,
The ferromagnetic metal film can be made of permalloy or the like.

The magnetic recording medium of the present invention includes a driving unit for rotating the magnetic recording medium, a magnetic head for recording and reproduction, means for moving the magnetic head relative to the magnetic recording medium, and signal reproduction from the output of the magnetic head. It is used by being incorporated in a magnetic recording / reproducing apparatus having means and the like.

[0014]

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

[0015]

【Example】

[Example 1] On a disk substrate made of an Al-Mg alloy coated with a nickel (Ni) and phosphorus (P) alloy plating film, a Ti-
After forming a 10 at% Cr alloy film, Co-19 at%
A 0.05 μm thick Co—Cr alloy magnetic thin film having a Cr composition was formed at a substrate temperature of 150 ° C. Further, a carbon film having a thickness of 0.015 μm was formed as a protective film.
A sample manufactured by such a method is referred to as a magnetic disk S1. The crystal structure of the manufactured alloy magnetic thin film was hexagonal, and it was confirmed by an X-ray diffraction apparatus that the c-axis was oriented in a direction perpendicular to the film surface.

Further, the substrate temperature at the time of forming a Co—Cr film by sputtering is set to 200 ° C. or 250 ° C.
Samples were prepared under the same conditions except that the temperature was set to 0 ° C., and the samples were used as disks S2, S3, and S4, respectively.

The magnetic properties of the sample thus prepared were measured with a vibrating sample magnetometer (VSM) to determine the saturation magnetization (Ms) and the coercive force (Hc). The direction of application of the magnetic field was perpendicular to the film surface. The results are summarized in FIG.

Further, in order to examine the composition distribution in the microscopic region of each sample, a high-resolution energy dispersive X-ray spectrometer (EDX) is used.
py) was used to measure the concentrations of the Cr element and the Co element at the crystal grain boundaries and inside the crystal. The electron beam diameter of the EDX device used for the measurement is about 1.5 nm, and the composition of a minute region having a diameter of about 2 nm can be measured. FIG. 3 shows the relationship between the Cr concentration at the grain boundaries of the disks S1 to S4 and the substrate temperature.

As can be seen from FIG. 2, the coercive force increases as the substrate temperature increases. In particular, 200 ° C to 250 ° C
Shows a rapid change in the range. On the other hand, as can be seen from FIG. 3, the Cr concentration at the grain boundary increases as the substrate temperature increases. In a disk manufactured at a substrate temperature of 200 ° C. or higher, the Cr concentration at the grain boundary was 21 at% or higher, and the sample was dissolved and the overall average composition of the film determined by chemical analysis was higher than 19 at%. This indicates that the segregation of the composition progresses in the process of forming the Cr film, and a region having a high Cr concentration is formed at the surface portion (grain boundary) of the particle. The dependence of the coercive force on the substrate temperature indicates that the coercive force is improved by reducing the magnetic interaction between particles due to segregation of nonmagnetic Cr atoms.

Next, the recording and reproducing characteristics of the manufactured disk were evaluated using a magnetic disk recording and reproducing tester.
The magnetic head used for recording and reproduction has a gap length of 0.2μ.
m, a track width of 4.5 μm, and a coil turn of 30 turns. Reproduction output and medium noise when "all 1" signals were recorded under the conditions of a distance between the medium facing surface of the head and the medium surface, a flying height of 0.06 μm, a peripheral speed of 10 m / s, and a linear recording density of 160 kFCI. Was measured. The result is shown in FIG.

The horizontal axis in FIG. 1 is the Cr concentration at the crystal grain boundaries obtained from the energy dispersive X-ray spectrometer. As is clear from the figure, the reproduction output was a Cr concentration of 23.5 at%.
The maximum value is shown in the vicinity. This value is lower than 25 at%, which was conventionally determined to be optimal. On the other hand, it can be seen that the medium noise sharply decreases as the Cr concentration increases, but that the difference is not so large when the Cr concentration is 22 at% or more.

The above results show that, from the viewpoint of the signal-to-noise ratio (S / N), the optimum range of the Cr concentration is approximately 21 to 24 at.
%. In this concentration range, the Co—Cr alloy segregated at the grain boundaries still has a weak spontaneous magnetization, and a weak exchange interaction is acting between adjacent grains. It is presumed that this interaction works effectively in improving the output. On the other hand, in the disk S4 in which the Cr concentration at the grain boundary is 25 at% or more, which has been conventionally optimized, the Co-Cr alloy is non-magnetic, and no exchange interaction occurs. This is considered to be a cause of deterioration of the reproduction output although the medium noise is low.

It is considered that the reproduction output is improved by adjusting the Cr concentration in the grain boundary as described above for the following reason. In perpendicular recording, in the vicinity of a magnetic transition region that is a boundary between recording bits, energy due to exchange interaction is dominant over magnetostatic energy. Therefore, it is more advantageous to shorten the length of the magnetization transition region in order to reduce the energy due to the exchange interaction. That is, rather than the magnetization transition region being disturbed zigzag,
It is easier for energy to be stable if it is linear. This improves the reproduction output in terms of magnetic recording. However, if an excessive exchange interaction is present, the magnetic domain size becomes large, so that high-density recording cannot be performed and media noise increases, which is not preferable.

As is clear from the above examples, in the Co—Cr alloy thin film for perpendicular recording, the surface (grain boundary) of the particles is used.
Is preferably set at 21 to 24 at% in view of reproduction output and S / N ratio.

[Embodiment 2] Next, also in a magnetic thin film obtained by adding Ta to a Co-Cr binary alloy, the Cr concentration at the boundary of the crystal grain was made 21 to 25 at% lower than the conventional 25 at% as in the first embodiment. This indicates that by setting the value to less than the above, a high reproduction output can be obtained without increasing the medium noise.

The preparation method of the sample is the same as that of the first embodiment, except that the Co-17a
A sputtering target having a composition of t% Cr-3at% Ta was used. The other manufacturing conditions were the same, and the substrate temperature was 170 ° C., 200 ° C., 250 ° C., as in Example 1.
A sample was prepared by changing the temperature to 300 ° C. The sample disks to which Ta was added were placed in the order of T1, T2, T
3, T4.

The sample disk T manufactured by the above method
The Cr concentration and recording / reproducing characteristics at the grain boundaries of 1, T2, T3, and T4 were measured in the same manner as in Example 1. Fig. 4 shows the results.
Shown in The relationship between the Cr concentration at the grain boundary, the reproduction output, and the medium noise is on a curve different from that in Example 1, but the same tendency as in Example 1 can be confirmed as is clear from the figure. That is, the Cr concentration at the grain boundary is 21 to 25.
In the range of at%, the medium noise is low and the output is high, and an S / N characteristic superior to that of the Co—Cr binary medium is obtained.

As described above, by adding Ta, C
More preferable results are obtained as compared with the o-Cr binary system because the segregation state of Cr at the crystal grain boundaries becomes uniform,
It is presumed that the fluctuation of the local exchange interaction is reduced.

Although the example in which Ta is added to the magnetic film has been described here, the elements to be added to the magnetic film are Ta, P
Similar effects were obtained with at least one element selected from the group consisting of t, Ni, Nd, B, and Si.

[Embodiment 3] Next, Co to be a magnetic recording layer
Examples 1 and 2 also apply to a so-called two-layer film medium using a permalloy layer as an underlayer for a Cr-based binary alloy magnetic thin film.
In the same manner as in
By setting it to less than t%, it is shown that a high reproduction output can be obtained without increasing the medium noise.

The sample was a 0.3 μm thick ferromagnetic film of permalloy (Ni-20 at% Fe) on a non-magnetic substrate instead of the Ti—Cr film used in Examples 1 and 2 as an underlayer. Is provided by a sputtering method, and Co-1
Co-Cr having a composition of 7 at% Cr-3 at% Ta
-It was produced by forming a Ta film by a sputtering method. The substrate temperature at the time of forming the permalloy film was constant at 200 ° C., and the substrate temperature at the time of forming the Co—Cr—Ta film was 170 ° C.
Four types of sample discs were prepared by changing the temperature to 200 ° C., 250 ° C., and 300 ° C.

The Cr and Ta element concentrations and the recording / reproducing characteristics at the grain boundaries of the sample disk manufactured by the above method were measured by the same method as in Example 1. As a result, the same result as that shown in FIG. Cr and Ta concentrations at grain boundaries and reproduction output,
And the relationship between media noise. That is, when the sum of the Cr and Ta elements at the grain boundaries was set to 21 at% or more, the medium noise was sharply reduced, and the reproduction output showed the maximum value near 24 at%. However, the absolute values of the reproduction output and the medium noise in this embodiment were about 1.5 times higher than those in the first and second embodiments due to the effect of the permalloy underlayer.

In place of Ta, Pt, Ni, Nd, B
The same effect was obtained in a Co—Cr-based magnetic film to which Si was added or in a Co—Cr-based magnetic film to which two or more of these elements were added.

[Embodiment 4] FIG. 5 is a schematic view showing an example of a magnetic recording / reproducing apparatus according to the present invention. Head disk
A plurality of magnetic disks 1 are mounted on a spindle shaft in an assembly 4 and a medium drive system (motor) 5
Is rotated at high speed. As the magnetic disk 1, the disk manufactured in the above embodiment was used. A magnetic head 2 for recording / reproducing a signal on / from a magnetic recording surface of the magnetic disk 1 is arranged, and one of them functions as a servo head. The magnetic head 2 includes a head drive system 6
Accordingly, the magnetic disk 1 is moved in a substantially radial direction via the actuator 3. The apparatus further includes a recording / reproducing system 7 for recording / reproducing data, a signal processing system 8 for processing the signals, a control system 9 for controlling these and the driving system, and exchange of data with a host device. A device I / F section 10 for performing the operation is provided.

Using this magnetic recording / reproducing apparatus, data was read out from the magnetic disk produced in any of the above-mentioned embodiments. As a result, a sufficiently high reproduction output and low medium noise could be obtained in each case.

[0036]

According to the present invention, according to the present invention, Co-
In a Cr-based thin film medium, the Cr concentration at the grain boundaries of the fine crystal grains constituting the magnetic thin film is 21 to 24 at% or 2 at%.
By setting it in the range of 1 to 25 at%, the reproduction output is improved without increasing the medium noise, and the signal-to-noise ratio (S
/ N) can be greatly improved. Further, the magnetic recording / reproducing apparatus using the magnetic disk according to the present invention has a high reproduction output and an S / N ratio.

[Brief description of the drawings]

FIG. 1 shows C at a grain boundary of a Co—Cr sputter disk.
FIG. 7 is a diagram showing the dependence of r density, reproduction output, and medium noise.

FIG. 2 is a diagram showing the substrate temperature dependence of the coercive force and saturation magnetization of a Co—Cr sputtered film.

FIG. 3 is a diagram showing the Cr concentration and the substrate temperature dependence at the grain boundaries of a Co—Cr sputtered film.

FIG. 4 is a diagram showing the dependence of Cr concentration at a grain boundary of a Co—Cr—Ta sputter disk, reproduction output, and medium noise.

FIG. 5 is a schematic view of an example of a magnetic recording / reproducing apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk, 2 ... Magnetic head, 3 ... Actuator, 4 ... Head disk assembly, 5 ... Medium drive system, 6 ... Head drive system, 7 ... Recording / reproducing system, 8 ... Signal processing system, 9 ... Control system , 10 ... Device I / F section

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaaki Nihon 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. The method according to claim 1, wherein the coating is performed directly on the non-magnetic substrate or via an intermediate layer made of a non-magnetic metal film or a ferromagnetic metal film.
And a magnetic recording medium provided with a Co—Cr-based alloy magnetic thin film containing Cr and Cr as a main component, wherein the magnetic thin film has a hexagonal crystal structure, and its c-axis is substantially perpendicular to or perpendicular to the thin film surface. A magnetic recording medium, which is inclined in one direction from the magnetic thin film and has a Cr concentration at a grain boundary of fine crystal grains which is a constituent unit of the magnetic thin film, higher than an average Cr concentration of the magnetic thin film and lower than 25 at%. 2. The magnetic recording medium according to claim 1, wherein the Cr concentration at the grain boundary is in the range of 21 to 24 at%. 3. The Co—Cr-based magnetic thin film is made of Ta, P
A Co—Cr-based alloy thin film to which at least one element selected from the group consisting of t, Ni, Nd, B, and Si is added, wherein the combined concentration of Cr and the third element at the grain boundary is 21 to 21. 2. The magnetic recording medium according to claim 1, wherein the content is less than 25 at%. 4. A magnetic recording medium according to claim 1, 2 or 3, a drive unit for rotating the magnetic recording medium, a magnetic head for recording and reproduction, and a magnetic head for moving the magnetic head with respect to the magnetic recording medium. A magnetic recording / reproducing apparatus comprising: means for causing relative movement; and means for reproducing a signal from an output of the magnetic head.