The present invention is a method for mass-production of a recording medium with the component composition thereof monotonically changing along the film thickness direction. In the method, the magnetic recording medium that includes at least a substrate, and first magnetic recording layer and second magnetic recording layer as the magnetic recording layer. The method includes: laminating a second magnetic layer of FePtRh on a first magnetic layer of FePt or FePtRh with heating. In the method, heat treatment may be preheat-treatment or postheat-treatment, when laminating the second magnetic layer of FePtRh onto the first magnetic layer of FePtRh, the concentration of Rh in the second magnetic layer is higher than that of the first magnetic layer.

A magnetic recording medium according to one embodiment includes an underlayer and a magnetic layer above the underlayer. The magnetic layer includes a first magnetic material and particulates. A protective layer is positioned above the magnetic layer, the protective layer including a second material. A magnetic recording medium according to another 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.

A magnetic device including: a magnetic reader; a magnetic writer; and a variable overcoat, the variable overcoat positioned over at least the magnetic reader and writer, the variable overcoat having an overcoat layer, the overcoat layer having a substantially constant thickness and material; and at least one disparate overcoat portion, the disparate overcoat portion having a different thickness, a different material, or both, than the overcoat layer.

The magnetic tape has a magnetic layer and a backcoat layer, wherein the Ra on the magnetic layer side surface is less than or equal to 1.8 nm, the coefficient of friction measured on the base portion of the magnetic layer side surface is less than or equal to 0.35, the Ra measured on the backcoat layer side surface is less than or equal to 5.0 nm, the backcoat layer contains a fatty acid ester, the FWHM.sub.before measured on the backcoat layer side surface before vacuum heating is greater than 0 nm but less than or equal to 10.0 nm, the FWHM.sub.after after vacuum heating is greater than 0 nm but less than or equal to 10.0 nm, and the difference between the spacing measured on the backcoat layer side surface after and before vacuum heating is greater than 0 nm but less than or equal to 8.0 nm.

The magnetic tape has a magnetic layer and a backcoat layer, wherein, each of the magnetic layer and backcoat layer contains a fatty acid ester, the Ra measured on the magnetic layer side surface is less than or equal to 2.8 nm, the difference between the spacing measured by optical interferometry on the magnetic layer side surface after and before vacuum heating is greater than 0 nm but less than or equal to 8.0 nm, the FWHM.sub.before on the backcoat layer side surface is greater than 0 nm but less than or equal to 10.0 nm, the FWHM.sub.after on the backcoat layer side surface is greater than 0 nm but less than or equal to 10.0 nm; and the difference between the spacing measured on the backcoat layer side surface after and before vacuum heating is greater than 0 nm but less than or equal to 8.0 nm.

Embodiments provide a polishing composition for a magnetic disc substrate including colloidal silica, a phosphorus-containing compound, a water-soluble polymer compound, and water. According to at least one embodiment, the water-soluble polymer compound is a copolymer having a structural unit derived from an unsaturated aliphatic carboxylic acid and a structural unit derived from an unsaturated amide.

A method for making an ordered magnetic alloy includes (a) providing a thermally conductive base having opposite first and second surfaces; (b) forming a thermal barrier layer on the first surface of the thermally conductive base; (c) forming a disordered magnetic alloy layer on the thermal barrier layer, the disordered magnetic alloy layer being made from a disordered alloy which contains a first metal selected from Fe, Co, and Ni, and a second metal selected from Pt and Pd; and (d) after step (c), applying a transient heat to the thermally conductive base to cause rapid thermal expansion of the thermally conductive base, which, in turn, causes generation of an in-plane tensile stress in the disordered magnetic alloy layer.

When a laser beam is used to perform shape processing on an edge surface of a disk-shaped glass plate, in order to suppress strain (retardation values) in the main surface of the glass plate, the disk-shaped glass plate is floated above a base, and the edge surface of the glass plate is processed into a target shape by irradiating the edge surface with the laser beam while contactlessly heating the glass plate in a state where the glass plate is floated, and moving the laser beam relative to the edge surface in the circumferential direction of the disk-shaped glass plate.

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 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.

Embodiments include a magnetic recording medium containing ε-type iron oxide particles and having excellent SNR, a manufacturing method of ε-type iron oxide particles, and a manufacturing method of a magnetic recording medium. High SNR is achieved by a magnetic recording medium containing ε-type iron oxide particles, in which a coefficient of variation of an aspect ratio of the ε-type iron oxide particles is equal to or smaller than 18%, and a squareness ratio of the magnetic recording medium measured in a longitudinal direction of the magnetic recording medium is higher than 0.3 and equal to or lower than 0.5. The object is also achieved by the application of the magnetic recording medium.