A magnetic disk substrate is composed of an aluminum alloy substrate, a base plating layer on a surface of the aluminum alloy substrate, and a boundary region between the aluminum alloy substrate and the base plating layer. The boundary region includes a specific boundary region (D(1).sub.I(50-84)) having Al emission intensities equal to 50% to 84% of an average Al emission intensity in an interior region of the aluminum alloy substrate in glow discharge optical emission spectroscopy in the depthwise direction from the surface of the magnetic disk substrate. The specific boundary region (D(1).sub.I(50-84)) has a maximum Fe emission intensity (I(1).sub.Fe(max)) higher than an average Fe emission intensity (I(1).sub.Fe(ave)) in the interior region of the aluminum alloy substrate in the glow discharge optical emission spectroscopy.

A dummy substrate is formed with a disk-shaped glass substrate having a center hole, and a magnetic recording film on an outer circumferential surface along a thickness direction of the glass substrate and an inner circumferential surface of the center hole, and a surface roughness (Ra) of one surface and the other surface of the glass substrate is in a range of 0.2 nm or more and 100 nm or less.

A polishing liquid for polishing a glass substrate includes cerium oxide as polishing abrasive particles, and a substance that reduces cerium oxide in response to irradiation of light.

An aluminum alloy sheet for a magnetic disk includes an aluminum alloy comprising 0.10 to 3.00 mass % (hereafter simply “%”) of Fe, 0.1 to 3.0% of Mn, 0.003 to 1.000% of Cu, and 0.005 to 1.000 s % of Zn, wherein second phase particles having a maximum diameter of 100 μm or more and 300 μm or less are dispersed at a distribution density of 50 particles/mm.sup.2 or less in a region (A) occupying 25% or less of a sheet thickness from a sheet thickness center plane to opposite surfaces of the sheet, second phase particles having a maximum diameter of 100 μm or more and 300 μm or less are 0 particles/mm.sup.2 in a region (C) that is obtained by excluding the region (A) from a region (B) occupying 50% or less of the sheet thickness from the sheet thickness center plane to the opposite surfaces of the sheet, and the amount of Mn solid solution is 0.03 mass % or more.

A magnetic-disk substrate has a pair of main surfaces, and an arithmetic average roughness Ra of each of the main surfaces is 0.11 nm or less. The arithmetic average roughness Ra is a value obtained through measurement using an atomic force microscope provided with a probe having a probe tip provided with a carbon nanofiber rod-shaped member. The magnetic-disk substrate is made of glass or aluminum alloy.

A method for polishing a glass substrate, by which a polishing speed that is higher than a conventional polishing speed can be maintained for a long period of time in processing for polishing a glass substrate using cerium oxide as polishing abrasive particles is provided. A polishing liquid containing cerium oxide as polishing abrasive particles is supplied to a polishing surface of a glass substrate, and the glass substrate is subjected to polishing processing. This polishing liquid contains the cerium oxide as polishing abrasive particles and a substance that reduces cerium oxide in response to light irradiation. Also, processing for irradiating the polishing liquid with light is performed when polishing processing is performed.

Provided is a sputtering target containing 0.05 at % or more of Bi, and having a total content of metal oxides of from 10 vol % to 70 vol %, the balance containing at least Ru.

A sheet-like spacer to be used when a laminate of a plurality of substrates is formed for the purpose of processing end faces of the substrates is provided between the adjacent substrates in the laminate to keep the adjacent substrates apart from each other. An area of the spacer is smaller than that of the substrates. A contact angle of a surface of the spacer with respect to pure water is 50° or less.

Embodiments provide a polishing composition for a magnetic disk substrate, the polishing composition containing colloidal silica, at least one of a phosphorus-containing inorganic acid and a phosphorous-containing organic acid, and water. According to at least one embodiment, the colloidal silica in the polishing composition has an average particle diameter (D50) in the range of 5 to 50 nm observed by a transmission electron microscope. In measuring a volume-based particle size distribution of the colloidal silica by dynamic light scattering, when the particle size distribution is measured by adjusting a concentration of colloidal silica particles to be 0.25 mass %, the colloidal silica contains 10 vol % or less of colloidal silica particles larger than 50 nm. The polishing composition has 1 to 50 mass % of the colloidal silica, and the pH (25° C.) in the range of 0.1 to 4.0. The colloidal silica is stabilized by sodium or ammonium.

Provided is an aluminium alloy substrate for a magnetic disk, a method for fabricating the substrate, and a magnetic disk composed of the aluminium alloy substrate for a magnetic disk. The substrate contains an aluminium alloy composed of one or more elements selected from a group comprising 0.05 to 3.00 mass % (hereinafter abbreviated as “%”) of Fe, 0.05% to 3.00% of Mn, 0.05% to 18.00% of Si, 0.05% to 8.00% of Ni, 0.05% to 3.00% of Cr, and 0.05% to 3.00% of Zr, with a balance of Al and unavoidable impurities. The substrate has a Young modulus of 67 GPa or more in each of the 0° direction, 45° direction, and 90° direction relative to the rolling direction of the substrate.