Letting a particle diameter be Dx (μm) when a cumulative particle volume cumulated from the small particle diameter side reaches x (%) of the total particle volume in a particle size distribution obtained regarding cerium oxide included in a polishing liquid using a laser diffraction/scattering method, D5 is 1 μm or less, D100 is 3 μm or more, D50 is 0.8 to 2.4 μm, and Dpeak−D5 is less than D95−Dpeak.

An aluminum alloy disc blank for a magnetic disc made of an aluminum alloy containing Fe: 0.005 to 1.800 mass % with the balance being Al and inevitable impurities, wherein a flatness change of the aluminum alloy disc blank for a magnetic disc when the aluminum alloy disc blank for a magnetic disc is held in the atmosphere at 50° C. or lower for 336 hours is 2.0 μm or less.

A sheet-like spacer to be used when a laminate of a plurality of subs rates 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.

Various apparatuses, systems, methods, and media are disclosed to provide a magnetic recording medium with a tungsten (W) pre-seed layer. The W pre-seed layer has a higher conductance than a CrTi pre-seed layer with a similar thickness. In one embodiment, the W pre-seed layer is made of about 95 atomic percent or more of W. The W pre-seed layer has lower electrical resistivity than the CrTi pre-seed layer. As a result, the thickness of the W pre-seed layer can be reduced as compared to the thickness of a CrTi pre-seed layer if a similar conductance is to be achieved. The magnetic recording materials deposited on top of the W pre-seed layer with the reduced thickness provide comparable crystallographic orientation and recording performance to those deposited on top of a thicker CrTi pre-seed layer with a similar conductance.

In one aspect, the present disclosure provides a method for producing an aluminum platter, which can improve the smoothness of the substrate surface before a magnetic layer is formed thereon and can provide a hard disk substrate that can be processed into a medium with a high yield. In another aspect, the present disclosure relates to a method for producing an aluminum platter, including the following steps 1 and 2: step 1: bringing a composition containing a compound (component A) that has at least one structure represented by the following formula (I) and has a molecular weight between 50 and 100,000 inclusive into contact with a substrate surface of a Ni—P plated aluminum alloy substrate; and step 2: forming a magnetic layer on the substrate obtained in the step 1. ##STR00001##

Chamfering processing for chamfering an edge face of a disk-shaped glass plate includes a step of disposing the glass plate such that a portion of the glass plate is disposed in a heating space for heating the glass plate and the remaining portion is disposed outside the heating space; and a step of softening a portion of the edge face of the glass plate by irradiating a circumferential portion of the edge face with a laser beam outside the heating space while rotating the glass plate in one direction around the center of the glass plate, and heating the softened portion of the edge face that has reached the heating space through the rotation.

A magnetic recording medium according to one embodiment includes a base film and a first nonmagnetic layer above the base film. The first nonmagnetic layer has first nonmagnetic particles. A second nonmagnetic layer is positioned above the first nonmagnetic layer, the second nonmagnetic layer having second nonmagnetic particles. A magnetic layer is positioned above the second nonmagnetic layer, the magnetic layer including a magnetic material.

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.

A method for manufacturing an annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm includes processing for manufacturing an annular glass plate by irradiating each of the outer circumferential edge surface and the inner circumferential edge surface of an annular glass blank with a laser beam to melt the outer circumferential edge surface and the inner circumferential edge surface and form molten surfaces such that the molten surfaces in the outer circumferential edge surface and the inner circumferential edge surface each have an arithmetic average surface roughness Ra not larger than 0.1 μm, and the surface roughness of the molten surface in the inner circumferential edge surface becomes larger than the surface roughness of the molten surface in the outer circumferential edge surface.

A magnetic-disk glass substrate contains an alkaline earth metal component as a glass composition and includes a pair of main surfaces, and an outer circumferential side edge surface that is a mirror surface. The outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more and 68% or less when a bearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured. A glass transition point of the glass composition that constitutes the magnetic-disk glass substrate is 700° C. or more. The glass composition that constitutes the magnetic-disk glass substrate is alkali-free glass.