This substrate for a magnetic recording medium has a metal structure made of an Al alloy having a composition including Si in a range of 28.0% by mass to 32.0% by mass, Cu in a range of 2.5% by mass to 4.0% by mass, and Mg in a range of 0.8% by mass to 1.5% by mass with a remainder being Al, primary-crystal Si particles having a maximum diameter of 0.5 m or more and an average particle diameter of 2 m or less are dispersed in the metallic structure, a diameter of the substrate is in a range of 53 mm to 97 mm, and a thickness of the substrate is in a range of 0.2 mm to 0.9 mm.

This aluminum alloy substrate for a magnetic recording medium has a metal structure made of an Al alloy having a composition including Si in a range of 18.0% by mass to 22.0% by mass, Ni in a range of 5.0% by mass to 8.5% by mass, Cu in a range of 2.5% by mass to 4.0% by mass, and Mg in a range of 0.8% by mass to 1.5% by mass with a remainder being Al, a primary-crystal Si precipitate having a maximum diameter of 0.5 m or more and an average particle diameter of 2 m or less is dispersed in the metal structure, a diameter is in a range of 53 mm to 97 mm, and a thickness is in a range of 0.2 mm to 0.9 mm.

A method for making a magnetic recording tape, in accordance with one approach, includes coupling an underlayer to a substrate, the substrate comprising a poly ether ether ketone (PEEK). A method for making a magnetic recording tape in accordance with another approach includes coupling an underlayer to a substrate via radiation-induced grafting, the substrate comprising a poly ether ether ketone (PEEK). A recording layer is coupled to the underlayer.

The area of a spacer that is to be provided between the adjacent substrates in a laminate including a plurality of substrates to keep the adjacent substrates apart from each other is smaller than those of the stacked substrates. When pressure is released to bring the laminate obtained by providing the spacers between the substrates from a pressed state in which 0.60 MPa of pressure is applied to the laminate in the stacking direction into a non-pressed state, an amount of change W in thickness per spacer that is calculated from a change in the thickness of the laminate due to the release of pressure is 30 m or less.

There are provided: an aluminum alloy substrate for a magnetic disk, in which the product of the sheet thickness and loss factor of the substrate is 0.710.sup.3 or more; a method for producing the aluminum alloy substrate for a magnetic disk; and a magnetic disk, in which an electroless NiP plating treatment layer and a magnetic layer formed thereon are disposed on a surface of the aluminum alloy substrate for a magnetic disk.

Disclosed is a perpendicularly magnetized film structure using a highly heat resistant underlayer film on which a cubic or tetragonal perpendicularly magnetized film can grow, comprising a substrate of a cubic single crystal substrate having a (001) plane or a substrate having a cubic oriented film that grows to have the (001) plane; an underlayer formed on the substrate from a thin film of a metal having an hcp structure in which the [0001] direction of the thin metal film forms an angle in the range of 42 to 54 with respect to the <001> direction or the (001) orientation of the substrate; and a perpendicularly magnetized layer located on the metal underlayer and formed from a cubic material selected from a Co-based Heusler alloy and a cobalt-iron (CoFe) alloy having a bcc structure a constituent material, and grown to have the (001) plane.

Embodiments provide a polishing composition containing colloidal silica, pulverized wet-process silica particles, and a water-soluble polymer compound. According to at leaset one embodiment, the water-soluble polymer compound is a copolymer containing a structural unit derived from an unsaturated aliphatic carboxylic acid and a structural unit derived from an unsaturated amide.

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 m is measured.

There are provided: an aluminum alloy magnetic disk substrate including: an aluminum alloy base material including an aluminum alloy containing 0.4 to 3.0 mass % (hereinafter, simply referred to as %) of Fe, 0.1 to 3.0% of Mn, 0.005 to 1.000% of Cu, and 0.005 to 1.000% of Zn, with the balance of Al and unavoidable impurities; and an electroless NiP plated layer formed on a surface of the aluminum alloy base material, in which the peak value (BLEI) of Fe emission intensity at an interface between the electroless NiP plated layer and the aluminum alloy base material, as determined by a glow discharge optical emission spectrometry device, is lower than Fe emission intensity (AlEI) in the interior of the aluminum alloy base material, as determined by the glow discharge optical emission spectrometry device; and a method for producing the aluminum alloy magnetic disk substrate.

An object of the present invention is to provide a magnetic recording medium, which contains -type iron oxide particles and has excellent SNR, a manufacturing method of -type iron oxide particles, and a manufacturing method of a magnetic recording medium.

The object is achieved by a magnetic recording medium containing -type iron oxide particles, in which a coefficient of variation of an aspect ratio of the -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.