Abstract: 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 256×256 pixels per 2 ?m square and/or (2) the number of foreign substances detected to have sizes of 0.1 ?m or more and 1.0 ?m or less upon detection of scattered light from the magnetic disk substrate when laser light with a wavelength of 405 nm is irradiated with a spot size of 5 ?m at a laser power of 25 mW 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 0.1 ?m or more and 1.0 ?m or less upon detection of the scattered light from the magnetic disk substrate when the laser light with the wavelength of 405 nm is irradiated with the spot size of 5 ?m at the laser power of 25 mW is 400 or less per 30 cm2 on the second main surface.

Abstract: It is an object to provide a magnetic disk substrate highly reliable to prevent the occurrence of crash failure even if a magnetic disk is rotated at high speed, and suitable for a hard disk that starts and stops by the load/unload method, and a magnetic disk using such a substrate. The representative structure of a magnetic disk substrate according to this invention is a disk-shaped glass substrate 10 having a generally flat main surface 11, an end face 12, a chamfered face 13 formed between the main surface 11 and the end face 12, and an offset portion, at the periphery of the main surface 11, raised or lowered with respect to a flat surface, other than the periphery, of the main surface 11, and characterized in that the magnitude of the offset portion is approximately uniform over the entire circumference of the glass substrate 10.

Abstract: To provide a magnetic-disk glass substrate manufacturing method that can reduce the inner diameter dimensional error.

Abstract: A method for manufacturing a glass substrate for a magnetic disk comprises mirror surface polishing and cleaning of a glass substrate, wherein polishing agent of which the principal component is rare-earth oxide with content of fluorine 5% by weight or less, is supplied to the glass substrate, the surface of the glass substrate is subjected to mirror surface polishing by relatively moving the polishing cloth and the glass substrate, then this glass substrate is brought into contact with a cleaning solution including ascorbic acid, fluorine ion, and sulfuric acid of 3% by weight or more, and the polishing agent is dissolved and removed. The concentration of the ascorbic acid included in the cleaning solution is 0.1% by weight or more, and the content of the fluorine ion is 1 ppm to 40 ppm. At least a magnetic layer is formed on the obtained glass substrate to manufacture a magnetic disk.

Abstract: In a method of processing a glass substrate for a magnetic disk, the glass substrate containing alkali ions, the glass substrate is processed by the use of a first alkali ion having a first ion radius greater than the smallest ion radius of the smallest alkali ion among the alkali ions contained the glass substrate. Subsequently, the glass substrate is processed by the use of a second alkali ion having a second ion radius greater than the first ion radius of the first alkali ion.