JP2000276731A - Vertical magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to decrease medium noises and to obtain a high S/N and stable recording signals by disposing a Cr alloy ground surface layer essentially consisting of Cr and containing at least Ta between a hard magnetic pinning layer and a nonmagnetic substrate. SOLUTION: The vertical magnetic recording medium consists of a four- layered structure formed by successively laminating the Cr alloy ground surface layer, the hard magnetic pinning layer, a soft magnetic ground surface layer and a vertical recording layer on the nonmagnetic substrate. The Cr alloy ground surface layer is a ground surface for the hard magnetic pinning layer to be formed thereon and at least Ta is incorporated into the Cr alloy to impart uniaxial magnetic anisotropy in the radial direction of the disk-shaped medium, by which Hc is enhanced. The influence by incoming magnetic fields can be lessened and the pinning effect of the hard magnetic pinning layer is improved by specifying the content of the Ta to >=6 at.%. The hard magnetic pinning layer is formed of Co or CoNi, CoNiCr, etc., on the Cr-based alloy ground surface layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a perpendicular magnetic recording medium having a three-layer structure having a perpendicular recording layer, a soft magnetic underlayer, and a hard magnetic pinning layer for fixing magnetic domains of the soft magnetic underlayer.

[0002]

2. Description of the Related Art The perpendicular recording method has attracted attention because it allows higher density recording than the current in-plane recording method.
Along with a single-layer film medium composed of a single perpendicular recording layer, a medium having a two-layer structure composed of a soft magnetic underlayer and a perpendicular recording layer has been studied. In particular, a medium with a two-layer structure can perform efficient recording / reproduction by combining with a single pole head. Above all, it is known that a two-layer film medium using a Co—Zr-based amorphous soft magnetic film as a base layer is particularly effective in improving the recording efficiency because a perpendicular recording layer having a sharp perpendicular orientation can be obtained ( JP-A-3-278595).

However, in the above-described perpendicular magnetic recording medium, particularly in a disk-shaped medium, there is a problem that the signal intensity is attenuated with time only by rotating the medium after recording the signal. . This phenomenon occurs because a magnetic field generated from a domain wall of the soft magnetic underlayer erases a recording signal of the perpendicular recording layer. In addition to it,
The magnetic field generated from the domain wall of the soft magnetic underlayer also has a problem that the medium noise also increases. Therefore, the present inventors provided an in-plane oriented hard magnetic pinning layer having magnetization in the radial direction between the substrate and the soft magnetic underlayer, and exchange-coupled with the soft magnetic underlayer to improve the recording / reproducing characteristics. A device in which demagnetization due to rotation of the medium is prevented and medium noise is reduced without loss has been proposed previously (Japanese Patent Application Laid-Open No. 7-129946).

A Co-based alloy having a chromium (Cr) underlayer is effective as the in-plane oriented hard magnetic pinning layer. This is because the exchange coupling can be increased by using the same Co alloy as the Co-Zr-based soft magnetic underlayer, and the magnetic orientation in the in-plane direction can be enhanced by providing the Cr underlayer. On the other hand, when CoSm is used as the in-plane oriented hard magnetic pinning layer, the magnetic orientation in the in-plane direction is high even without a Cr underlayer, and when the medium is disk-shaped, uniaxial magnetic anisotropy occurs in the radial direction of the medium. Since it has anisotropy, a particularly large pinning effect can be obtained.

[0005]

However, when the in-plane oriented hard magnetic pinning layer is made of CoSm having uniaxial magnetic anisotropy in the radial direction, the coercive force Hc in the easy axis direction (radial direction) becomes large. It is thermally unstable and drops to about 50 to 100 [Oe] in a stabilized state. When the Hc of the pinning layer is low, the switching field is further reduced due to exchange coupling, and the pinning layer is easily reversed by an external floating magnetic field. When the pinning layer causes the magnetization reversal, the exchange-coupled soft magnetic layer also undergoes a magnetization reversal, so that a magnetic domain wall is generated. For the above-described reason, signal degradation and medium noise are caused.

When the pinning layer is a Co-based alloy having a Cr underlayer, Hc can be higher than that of CoSm. However, in this system, when the medium is disk-shaped, the medium has uniaxial magnetic anisotropy in the circumferential direction of the medium, or has random orientation with no anisotropy in a specific direction in the in-plane direction. In this case, when the soft magnetic layer undergoes magnetization reversal due to an external magnetic field, the exchange-coupled pinning layer tends to undergo partial magnetization reversal, causing signal degradation and medium noise as in the case of CoSm.

[0007]

According to the present invention, a hard magnetic pinning layer, a soft magnetic underlayer, and a perpendicular recording layer are laminated on a non-magnetic substrate. In a perpendicular magnetic recording medium having a three-layer structure, C containing Cr as a main component and at least tantalum (Ta) is provided between the hard magnetic pinning layer and the nonmagnetic substrate.
One provided with an r-based alloy underlayer is provided. In this configuration, when the content of Ta in the Cr-based alloy underlayer is 6 atomic% (at%) or more, it is more effective in improving the pinning effect. Further, in the above configuration, the axis of easy magnetization of the Cr-based alloy underlayer is preferably substantially perpendicular to the running direction of the magnetic head.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The perpendicular magnetic recording medium of the present invention comprises a Cr-based alloy underlayer, a hard magnetic pinning layer, a soft magnetic underlayer, and a perpendicular recording layer laminated in this order on a nonmagnetic substrate. Having a four-layer structure. The Cr-based alloy base layer serves as a base for a hard magnetic pinning layer formed thereon and is formed of an alloy containing Cr as a main component. It is necessary that this Cr-based alloy contains at least Ta, whereby, for example, uniaxial magnetic anisotropy is provided in the radial direction of a disk-shaped medium, and Hc can be increased. Therefore, the influence of the external magnetic field can be reduced, and the pinning effect of the hard magnetic pinning layer described later can be significantly improved. It is preferable that the content of Ta is 6 at% or more, since such an effect becomes more remarkable. The Ta-containing Cr-based alloy underlayer as described above is particularly effective when applied to a material having a textured structure formed on the surface of a disk-shaped substrate in the circumferential direction for the purpose of preventing the magnetic head from sticking to the disk. It is a target.

[0009] A hard magnetic pinning layer is formed on the Cr-based alloy underlayer. The hard magnetic pinning layer has a function of fixing a magnetic domain of a soft magnetic underlayer formed subsequently. For example, Co or CoNi, CoNiC
r, CoNiPtP, CoCr, CoCrTa, CoC
A Co-based alloy such as rTaPt, CoPt, and CoCrPt is preferable. Further, the soft magnetic underlayer is preferably formed of a Co-Zr-based amorphous alloy such as CoZrNb and CoZrTa. Further, the perpendicular recording layer is made of, for example, a Co-P alloy, Co-N
i-P alloy, Co-γ-Fe ₂ O ₃ alloy, or
It is preferable to be formed of a Co—Cr-based alloy such as CoCrTa, CoCrPt, and CoCrTaPt. The perpendicular magnetic recording medium having such a configuration can be manufactured, for example, by forming each of the above layers on a non-magnetic substrate using a magnetron sputtering method.

<Embodiments> The present invention will be specifically described by the following embodiments. As a substrate, NiP was electrolessly plated on a disk-shaped Al substrate with a diameter of 95 mm.
Texture polishing was performed in the circumferential direction, and the average surface roughness (R _a ) in the radial direction was set to 5.5 nm. A Cr-based alloy base layer and a hard magnetic pinning layer were formed thereon. For the film formation, a DC magnetron sputtering apparatus having a φ152 mm cathode was used. The erosion area is distributed in a range of ± 15 mm around a position of φ105 mm. 110mm distance between target and substrate
And The film was formed under the conditions of an ultimate vacuum degree of 4 × 10 ⁻⁶ Torr or less, a substrate temperature of 200 ° C., and an Ar gas pressure of 5 mmTorr.

First, as a Cr-based alloy underlayer, CrTa
A layer having a thickness of 100 nm was formed. Subsequently, a layer made of CoNi _6.4 Pt _6.1 P ₆ at% was used as a hard magnetic pinning layer.
nm. The composition of the CrTa underlayer, that is, the Ta content was adjusted by the number of Ta chips arranged on the Cr target. The magnetic properties of the hard magnetic pinning layer thus obtained were evaluated using a vibrating sample magnetometer (VSM). The measurement was performed in each of the circumferential direction (Cir.) And the radial direction (Rad.) Of the disk.

FIG. 1 shows the relationship between the Ta content of the CrTa underlayer and the coercive force Hc. FIG. 2 shows the Ta content of the CrTa underlayer and the squareness ratio Rs (the ratio of the residual magnetization Mr to the saturation magnetization Ms;
(Mr / Ms) and the coercive force squareness ratio S ^* are shown. As a result, in the case of the underlayer formed of Cr alone without any Ta, Cir. Is Rad. It was confirmed that the magnetic anisotropy was higher in the circumferential direction. This is due to the influence of the texture structure in the circumferential direction of the substrate. On the other hand, when the Ta content is about 6 at%, the Cir. And Rad. Became almost the same, and it became clear that the film became magnetically random in the in-plane direction, and that the film became anisotropic in the radial direction when the Ta content became 6 at% or more.

Incidentally, when the Ta content is further increased, H
Although c decreases, it is still 1000 [Oe] or more, and since it has anisotropy in the radial direction, it was confirmed that it was sufficiently useful as a pinning layer. In this embodiment, a substrate having a texture structure in the circumferential direction is used as the substrate.For example, if a substrate having no texture structure such as glass is used, the magnetic anisotropy in the radial direction is further increased. Therefore, a larger pinning effect can be obtained.

[0014] Next, these Cr
The structure analysis of the Ta film was performed. FIG. 3 shows an X-ray diffraction pattern when the Ta content was changed. As the Ta content increases, the crystal orientation of Cr (200) changes from Cr (200) to Cr (110), and it can be seen from the movement of 2θ that the interplanar spacing increases. On the other hand, no crystal plane of Co appears. Originally, Co (10) was placed on Cr (110).
1) should grow. That is, the addition of Ta increased the magnetic anisotropy in the radial direction because of the effect of the flying direction of sputtered particles during film formation and the spread of the Cr-110 plane spacing, and the effect of the addition of Ta on the axis of easy magnetization. This is due to the fact that the c-axis of a certain Co is easily oriented in the radial direction. That is, while the center of the erosion area is the position of φ105 mm,
Since the substrate has a diameter of 95 mm, the flying direction of the sputtered particles is mainly due to the radial direction within the disk surface. Thereby, the axis of easy magnetization of the CrTa-based underlayer can be set substantially perpendicular to the running direction of the magnetic head.

As described above, the C is formed under the hard magnetic pinning layer.
When the rTa-based underlayer is formed, uniaxial anisotropy is provided in the radial direction of the disc-shaped medium, and Hc of the pinning layer increases. As a result, a large pinning effect is obtained, and the stability of the recording signal with respect to an external magnetic field is improved. In addition, the occurrence of medium noise is prevented, and a high S / N
Can be realized.

[0016]

As described above in detail, according to the present invention, since a Cr-based alloy containing Ta is used as an underlayer of a hard magnetic pinning layer, medium noise can be reduced and high S / N, and the stability of the recording signal with respect to an external magnetic field can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Ta content of a CrTa underlayer and the coercive force Hc.

FIG. 2 is a graph showing the relationship between the Ta content of a CrTa underlayer, the squareness ratio Rs, and the coercive force squareness ratio S ^* .

FIG. 3 is a diagram showing an X-ray diffraction pattern when the Ta content is changed.

Claims (3)

[Claims] 1. A hard magnetic pinning layer on a non-magnetic substrate,
3 composed of a soft magnetic underlayer and a perpendicular recording layer laminated
In a perpendicular magnetic recording medium having a layer structure, between the hard magnetic pinning layer and the nonmagnetic substrate, Cr is a main component,
A perpendicular magnetic recording medium characterized by having a Cr-based alloy underlayer containing at least Ta. 2. The perpendicular magnetic recording medium according to claim 1, wherein the content of Ta in the Cr-based alloy underlayer is 6 atomic% or more. 3. The perpendicular magnetic recording medium according to claim 1, wherein the axis of easy magnetization of the Cr-based alloy underlayer is substantially perpendicular to the running direction of the magnetic head.