Patent ID: 9105293
Filing Date: 2015-08-11
Classification: G11B

Abstract:
1. A glass substrate for a magnetic disk, wherein, in regions with respect to two places arbitrarily selected on a surface of the glass substrate on a central portion side relative to an outer peripheral end, a surface shape with a shape wavelength in a band of 60 to 500 μm is extracted from surface shapes in each of the regions and, assuming that a root mean square of the surface shape is given as a microwaviness (MW-Rq), a difference between the microwavinesses (MW-Rq) of the regions is 0.02 nm or less, wherein the two places are an outer peripheral end portion of the disk and a central portion of a recording/reproducing area of the disk, wherein the outer peripheral end portion of the disk is a region failing within a predetermined distance inward and outward from a point located 1.0 mm inward from an outer peripheral end of the disk toward a center of the disk, wherein the microwaviness (MW-Rq) is measured using a laser Doppler vibrometer, wherein an average value of the microwaviness (MW-Rq) on a main surface of the glass substrate is 0.4 nm or less, and wherein a ratio between the microwaviness (MW-Rq) of the regions is 1.1 or less.