MAGNETIC DISK SUBSTRATE AND MAGNETIC DISK

摘要

In a magnetic disk substrate being annular and having a first and a second main surface, (1) surface roughness measured by an atomic force microscope having a resolution of 256x256 pixels per 2μm square and/or (2) the number of foreign substances detected to have sizes of 0.1μm or more and 1.0μm or less upon detection of scattered light from the magnetic disk substrate when laser light with a wavelength of 405nm is irradiated with a spot size of 5μm at a laser power of 25mW differ/differs between the first and the second main surfaces. Only the first main surface has a surface quality usable as a magnetic recording surface. The number of the foreign substances detected to have the sizes of 0.1μm or more and 1.0μm or less upon detection of the scattered light from the magnetic disk substrate when the laser light with the wavelength of 405nm is irradiated with the spot size of 54m at the laser power of 25mW is 400 or less per 30cm2 on the second main surface.