JP2508639B2 - Perpendicular magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention is used in a so-called perpendicular magnetization recording system for recording and reproducing signals by utilizing residual magnetization in a direction perpendicular to a recording medium surface. The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium having a two-layer structure in which a soft magnetic layer such as a NiFe alloy thin film and a perpendicular magnetic anisotropic layer such as a COCr alloy thin film are sequentially laminated. .

[Outline of the Invention] The present invention provides a perpendicular magnetic recording medium comprising a non-magnetic support and a soft magnetic layer and a perpendicular magnetic anisotropy layer sequentially laminated on the non-magnetic support. By setting the anisotropy of reversible magnetic permeability obtained from the inclination to 23% or less, it is intended to provide a disk-shaped perpendicular magnetic recording medium having a small reproduction envelope modulation.

[Conventional technology]

Conventionally, in order to record / reproduce on / from a magnetic recording medium used as a recording medium such as a storage medium of a computer, an audio tape recorder, a video tape recorder, etc., a magnetic layer adhered and formed on a substrate is horizontally oriented. Magnetization (in-plane direction magnetization) is generally performed, and recording / reproduction is performed by residual magnetization in the in-plane direction.

However, in the case of recording by the in-plane magnetization, as the recording signal becomes shorter in wavelength, that is, as the recording density increases, the demagnetizing field in the medium increases, the residual magnetic flux density decreases, and the reproduction output decreases. Have.

Therefore, conventionally, a perpendicular magnetization recording method has been proposed in which recording and reproduction are performed by magnetization in the thickness direction of the magnetic layer of the magnetic recording medium. According to this perpendicular magnetization recording method, the demagnetizing field is reduced as the recording wavelength becomes shorter. Has become smaller, which is more advantageous in high-density recording than the above-mentioned recording by in-plane magnetization, and therefore, research is being actively conducted.

As a perpendicular magnetic recording medium used in this type of recording method, it is considered that a perpendicular magnetic anisotropic layer is formed of a CO-Cr alloy material or the like on a non-magnetic support such as a polymer film, Among them, Ni is used as an in-plane magnetized layer between the non-magnetic support and the perpendicular magnetic anisotropy layer which is a substantial recording / reproducing layer.
A two-layer perpendicular magnetic recording medium provided with a high-permeability thin film layer (soft magnetic layer) made of Fe alloy or the like has been attracting attention in terms of device configuration, recording sensitivity, reproduction efficiency, and the like.

By the way, it is already known that when the perpendicular magnetic recording medium having the two-layer structure is used in the shape of a disk, modulation due to the magnetic anisotropy of the soft magnetic layer occurs. That is, as shown in FIG. 2, the soft magnetic layer has in-plane magnetic anisotropy and has an MH loop in the easy axis direction (curve E in FIG. 2).
A) and MH loop in the difficult axis direction (curve HA in Fig. 2)
In a disk-shaped perpendicular magnetic recording medium such as a floppy disk, the output voltage is low when the magnetic head passes in the easy magnetization axis direction, and the output voltage becomes high when it passes in the hard magnetization axis direction. , Two peaks on the playback envelope while the magnetic head goes around the track,
It is observed that there are two valleys. This is a big problem in obtaining a constant output.

Under such circumstances, studies on the above-mentioned modulation have been repeated. For example, Japanese Patent Application Laid-Open No. 60-38718 discloses a method for obtaining the condition for reducing the modulation only from the magnetostatic characteristics of the medium. That is, this method is a method of obtaining from the major MH loop measured in the easy axis direction and the hard axis direction of the soft magnetic layer, and 1) the in-plane coercive force of the soft magnetic layer is 15 (Oe) or less. 2) The coercive force in the direction of easy axis of magnetization is 1.2 times or less of the coercive force in the direction of hard axis of magnetization orthogonal to the direction, 3) The magnetic field axis of the magnetization curve of the magnetization curve in the in-plane direction The main point is that the maximum value of the gradient of the tangent line at the intersection of is less than 2.5 times the small value.

[Problems to be solved by the invention]

However, as a result of repeated experiments by the present inventors, the conditions described in JP-A-60-38718 are not necessarily the conditions for obtaining a low modulation medium,
We came to the conclusion that there is room for further improvement.

The present invention aims to clarify the condition of the magnetic characteristics of the soft magnetic layer in order to reduce the modulation of the reproducing emblobe of a disk type perpendicular magnetic recording medium such as a floppy disk, and thereby to obtain an anisotropic reproduction output. An object is to provide a small number of perpendicular magnetic recording media.

[Means for solving problems]

As a result of repeated studies on the magnetic characteristic condition of the soft magnetic layer for suppressing the modulation of the perpendicular magnetic recording medium to a size that can be practically used, the present inventors have found that the reversible permeability obtained from the inclination of the minor loop in the remanent magnetization state. It has been found that the modulation can be suppressed to 3 dB or less by setting the magnetic anisotropy to 23% or less.

The perpendicular magnetic recording medium of the present invention has been completed based on such findings, and in a perpendicular magnetic recording medium comprising a nonmagnetic support, a soft magnetic layer and a perpendicular magnetic anisotropic layer are sequentially laminated, The anisotropy of reversible magnetic permeability obtained from the inclination of the minor loop in the remanent magnetization state of the soft magnetic layer is 23% or less.

The perpendicular magnetic recording medium to which the present invention is applied has a two-layer structure in which a perpendicular magnetic anisotropic layer made of a CO--Cr alloy or the like is sequentially formed on a soft magnetic layer made of a NiFe alloy or the like as a high magnetic permeability layer. Although it is a perpendicular magnetic recording medium, the materials of the soft magnetic layer and the perpendicular magnetic anisotropic layer are not limited to these.
Any medium that is normally used for this type of medium can be used.

In this perpendicular magnetic recording medium having a two-layer structure, the magnetic characteristics of the soft magnetic layer depend on the sputtering conditions and the like. By providing the directionality, the anisotropy of reversible permeability can be suppressed to 23% or less.

[Action]

As a means for evaluating the soft magnetic layer in the perpendicular magnetic recording medium having a two-layer structure, the present inventors have focused on the reversible magnetic permeability in the remanent magnetization state which is considered to be close to the state in which the actual soft magnetic layer is placed. .

This reversible permeability μ _r is the change of the magnetic field Δ as the inclination of the minor loop (curve M1 in FIG. 1) as shown in FIG.
It is calculated from H and the change in magnetic flux density ΔB according to μ _r = ΔB / ΔH (1) (where ΔB = 4πΔM + ΔH).

Here, the minor loop is the remanent magnetization state of the major loop (curve MJ in FIG. 1) (point indicated by Mr in FIG. 1).
It was a minor loop in. According to the experiments by the present inventors, the reversible permeability μ _r obtained from the inclination of the minor loop in this remanent magnetization state sensitively reflects the magnetic characteristics of the soft magnetic layer of the perpendicular magnetic recording medium having a double-layer structure. However, if the ratio of the reversible permeability μ _rh in the hard axis direction to the reversible permeability μ _Re in the easy axis direction is μ _rh / μ _re ≦ 1.23, the modulation falls below the practical level of 3 dB. It turned out to be suppressed.

Moreover, if the soft magnetic layer is evaluated by the above-mentioned reversible magnetic permeability, the accuracy is higher than that of the conventional method, and since the magnetostatic characteristics are used, a highly sensitive and highly accurate measuring instrument such as a vibrating sample type magnetometer can be used. It has a number of advantages such as the fact that modulation can be known only by measuring the magnetic properties of the medium.

〔Example〕

Hereinafter, the present invention will be described with reference to specific examples. Needless to say, the present invention is not limited to these examples.

(1) Method of manufacturing perpendicular magnetic recording medium A 50 μm thick polyethylene terephthalate substrate was coated with Ni.
An Fe-based soft magnetic layer was deposited and formed so as to have a thickness of 0.5 μm. Then, CO-as a perpendicular magnetic anisotropic layer on the soft magnetic layer
A Cr film was formed to a thickness of 0.15 μm. These films were formed on both sides of the substrate.

The continuous high-speed sputtering method by the DC magnetron method and the batch type RF sputtering method were adopted as the method for forming the film. The film formation rate is per minute for the DC magnetron method
4000 Å, batch type RF sputtering method 50 Å per minute
And

Further, a protective film and a lubricant layer were provided on the surface of the CO-Cr film to obtain a perpendicular magnetic recording medium.

According to the above method, the background pressure during the preparation of the soft magnetic layer was controlled to control the anisotropy of the soft magnetic layer, and various samples were prepared.

At this time, the background pressure was specifically controlled as follows. First, steam was introduced into the sputtering system to reach 10 ^-6 TOrr.
The pressure was adjusted to be about the same. Next, in order to increase the coercive force Hc of the soft magnetic layer, O ₂ gas is further introduced into the sputtering apparatus so that the coercive force is adjusted to a pressure of about 10 ⁻⁶ to 2 × 10 ⁻⁵ TOrr. In order to reduce Hc, N ₂ gas is further introduced into the sputtering device and 10 ⁻⁶ to 2 × 10 ⁶ is similarly added.
The pressure was adjusted to about ^-5 TOrr.

Reversible magnetic permeability and electromagnetic conversion characteristics (particularly modulation) of these samples were measured.

(2) Measurement of reversible magnetic permeability For each sample, cut out small pieces of 5 mm square from the center of the medium, dissolve one side of these pieces with acid, and a state where a soft magnetic layer and a perpendicular magnetic anisotropy layer are laminated only on one side. The sample of was produced. Then, for these samples, the magnetic characteristics of the soft magnetic layer in each in-plane direction were measured by a vibrating sample magnetometer. As shown in FIG. 1, the reversible magnetic permeability was calculated according to μ _r = ΔB / ΔH from the slope of the minor loop when the magnetic field of about 1.0 Oersted was changed in the remanent magnetization state. Here, μ _rh is the reversible permeability in the direction of hard magnetization, and μ _re is the reversible permeability in the direction of easy magnetization.

At the same time, the coercive force Hc _h in the hard axis direction, the coercive force Hc _e in the easy axis direction, and their ratio Hc _e / Hc _h from the major loop, and the magnetic field axis of the magnetization curve of the magnetization curve The ratio L _e / L _h of the maximum value L _e and the minimum value L _h of the tangent gradient at the intersection with and was also examined.

(3) Measurement of electromagnetic conversion characteristics Magnetic head: Single magnetic pole type perpendicular magnetic head Main magnetic pole: CO-Zr-Nb thin film 0.3 μm thickness Saturation magnetic flux density Bs about 12000 gauss Sample: Disk type double sided perpendicular magnetic recording medium (Sample 1 ~ Sample 10 and comparative sample 1 to comparative sample 6) Magnetic head / medium relative velocity: 6 m / Sec CO-Cr film coercive force: 450 to 1060 (0e) Decibels at recording wavelength 1.0 μm under the above measurement conditions The maximum value Ep _maX and the minimum value Ep _min of the displayed playback output were _calculated and Ep _max −Ep _min was defined as the modulation (unit: dB).

For each sample obtained by the above method (1),
The following table shows the results of measurement under the conditions (2) and (3).

In Samples 1 to 10 in the table, the ratio of the reversible permeability μ _rh in the hard axis direction to the reversible permeability μ _{re in} the easy axis direction is 1.23.
Below, the modulation at this time is 2.2 dB or less. On the other hand, in Comparative samples 1 to 6, the modulation is 3.2 dB or more, and at this time, μ _rh / μ _re exceeds 1.23.

It should be noted that although the measurement here is performed at a recording wavelength of 1.0 μm, it has been confirmed that similar results can be obtained for modulation even at recording wavelengths of 0.5 μm and 10 μm.

〔The invention's effect〕

As is clear from the above description, according to the present invention,
By defining the reversible magnetic permeability of the soft magnetic layer, which is a high magnetic permeability layer, a perpendicular magnetic recording medium having small anisotropy in reproduction output can be realized.

[Brief description of drawings]

FIG. 1 is a characteristic diagram for explaining reversible magnetic permeability, and FIG. 2 shows the MH loop in the easy axis direction and the MH loop in the hard axis direction in a perpendicular magnetic recording medium having a two-layer structure. It is a characteristic view to show.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ippie Kawazoe 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (56) References JP-A-60-202527 (JP, A) JP Sho 60-38718 (JP, A)

Claims (1)

(57) [Claims] 1. A perpendicular magnetic recording medium in which a soft magnetic layer and a perpendicular magnetic anisotropy layer are sequentially laminated on a non-magnetic support, and the soft magnetic layer is obtained from the inclination of a minor loop in the remanent magnetization state. A perpendicular magnetic recording medium having anisotropy of reversible magnetic permeability of 23% or less.