PERMANENT MAGNETIC CIRCUIT, AXISYMMETRIC MAGNETIC FIELD GENERATING METHOD, AND MANUFACTURING METHOD FOR PERPENDICULAR MAGNETIC RECORDING MEDIUM

Abstract

A magnetic field generating method and a permanent magnetic circuit for, using magnetic field heat treatment, imparting axisymmetric anisotropy in a direction parallel to the substrate to a soft magnetic body, particularly a soft magnetic backing layer for a perpendicular two-layered magnetic recording medium used in perpendicular magnetic recording. In a rare earth permanent magnetic circuit that exhibits hardly any demagnetization at high temperature, a plurality of magnet side faces 95 orthogonal to pole faces 94 are disposed with space therebetween. A magnetic field that is substantially antiparallel to magnetization 91 is generated in the space, and an unprocessed sample is inserted. Further, the permanent magnetic circuit with the unprocessed sample inserted therein is placed in a heat treatment furnace, and the unprocessed sample is rotated 96 as desired.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are respectively schematic cross-sectional views showing a layer configuration of a perpendicular magnetic recording medium and a longitudinal magnetic recording medium.

FIG. 2 is an exemplary configuration of a substrate for a magnetic recording medium with a soft magnetic backing film formed thereon.

FIG. 3 is a schematic view showing the magnetic anisotropy of a soft magnetic backing film.

FIGS. 4A to 4C are schematic views showing the form of magnetic fields generated by permanent magnets.

FIGS. 5A and 5B are schematic views respectively showing the shape of axisymmetric magnetic fields typified by a radial magnetic field and a circumferential magnetic field.

FIG. 6 is a schematic view showing a radial magnetic field resulting from like poles opposed to each other.

FIG. 7 is a schematic view showing a circumferential magnetic field being generated around a conductive wire.

FIG. 8A is a schematic perspective view showing an embodiment of the magnetic circuit of the present invention with permanent magnets disposed so that the magnetic field direction in the gap between the magnets may be radially axisymmetric, while FIG. 8B is a cross-sectional view at a B-B cross-section of the magnetic circuit shown in FIG. 8A with unprocessed samples passed through by a support rod and set in the magnetic circuit.

FIG. 9A is a schematic perspective view showing an embodiment of the magnetic circuit of the present invention with permanent magnets disposed so that the magnetic field direction in the gap between the magnets may be circumferentially axisymmetric, while FIG. 9B is a cross-sectional view at a B-B cross-section of the magnetic circuit shown in FIG. 9A with unprocessed samples passed through by a support rod and set in the magnetic circuit.

FIGS. 10A and 10B are schematic perspective views respectively showing embodiments of the magnetic circuit of the present invention that enable axisymmetric anisotropy to be imparted radially and circumferentially by rotating unprocessed samples.

FIGS. 11A and 11B respectively show with vectors the direction and the amplitude of the magnetic flux generated in the gap in the magnetic circuits of FIGS. 8A and 9A.

FIG. 12 is a schematic view showing an embodiment of a method for fixing a sample.

Claims

1. A permanent magnetic circuit for applying a magnetic field in a gap between opposing side faces of two or more rare earth permanent magnets, wherein the side faces are orthogonal to pole faces of the magnets and a direction of the magnetic field generated in the gap is opposite to a magnetization direction of the rare earth permanent magnets in a center equally distant from two opposing side faces on a central axis connecting an intersection of diagonals of the opposing magnet side faces, and irreversible demagnetization when exposed to a temperature of 150° C. to 350° C. inclusive is 5% or less.

2. The permanent magnetic circuit according to claim 1, wherein the rare earth permanent magnets are 2:17 SmCo magnets with a coercive force of at least 10 kOe, or Nd—Fe—B magnets with a coercive force of at least 20 kOe.

3. The permanent magnetic circuit according to claim 1, wherein the rare earth permanent magnets are mechanically fixed without using adhesive.

4. A magnetic field heat treatment apparatus comprising a permanent magnetic circuit as claimed in claim 1 inside a heat treatment furnace.

5. A method for generating an axisymmetric magnetic field comprising steps of: inserting a disk-shaped sample that has a soft magnetic backing layer formed on a disk-shaped substrate into the gap in the permanent magnetic circuit as claimed in claim 1,aligning the center of the disk-shaped sample with the rotational axis of the magnetic circuit, androtating the disk-shaped sample around the rotational axis.

6. A manufacturing method for a perpendicular magnetic recording medium comprising a substrate and layers formed on the substrate comprising a soft magnetic backing layer having an axisymmetric magnetic anisotropic distribution, a recording layer, a protective layer and a lubricating layer from a substrate side to an outer side, the method comprising the steps of: forming an unprocessed sample comprising the substrate and the soft magnetic backing layer thereon comprising a soft magnetic material;inserting the unprocessed sample into the gap in the permanent magnetic circuit as claimed in claim 1 so as to align the center of the unprocessed sample with a rotational axis of the permanent magnetic circuit; andheat-treating the center-aligned unprocessed sample and the permanent magnetic circuit inside a furnace at a desirable temperature.

7. The manufacturing method for a perpendicular magnetic recording medium according to claim 6, further comprising a step of rotating the unprocessed sample around the central axis of the permanent magnetic circuit.

8. The manufacturing method for a perpendicular magnetic recording medium according to claim 6, wherein the unprocessed sample is disk-shaped.

9. The manufacturing method for a perpendicular magnetic recording medium according to claim 6, wherein the desirable temperature in the step of heat-treating is 150° C. to 350° C., and a magnetic field strength generated in the gap in the permanent magnetic circuit is 50 Oe or more at the center.