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AssigneeFuji Electric Device Technology Co., Ltd.
InventorsHiroyuki Uwazumi, Youichi Tei, Kengo Kainuma, Kazuhito Higuchi, Akira Iso, Hajime Kurihara
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A disk substrate for a perpendicular magnetic recording medium is, disclosed. The substrate exhibits sufficient productivity, serves the function of a soft magnetic backing layer of the perpendicular magnetic recording medium, and scarcely generates noise. A perpendicular magnetic recording medium using such a substrate also is disclosed. The disk substrate comprises at least a soft magnetic underlayer formed on a nonmagnetic base plate by means of an electroless plating method. The thermal expansion coefficient of the soft magnetic underlayer is larger than a thermal expansion coefficient of the nonmagnetic disk-shaped base plate. A saturation magnetostriction constant λs satisfies a relation λs≧−1×10−5.
A disk substrate for a perpendicular magnetic recording medium comprising a soft magnetic underlayer formed on a nonmagnetic disk-shaped base plate by means of an electroless plating method, wherein a thermal expansion coefficient of the soft magnetic underlayer is larger than a thermal expansion coefficient of the nonmagnetic disk-shaped base plate and a saturation magnetostriction constant As satisfies a relation As≧−1×10−5, wherein the soft magnetic underlayer exhibits a ratio Mrrδ/Mrcδ is in a range of 0.33 to 3.00, in which Mrrδ is a product of the thickness and residual magnetization obtained from a magnetization curve measured by applying a magnetic field along a circumferential direction of the disk substrate, and Mrrδ is a product of the thickness and residual magnetization obtained from a magnetization curve measured by applying a magnetic field along a radial direction of the disk substrate.
Dependencies are inferred from the claim text.