A magnetic-disk substrate has a pair of main surfaces and arithmetic average roughnesses Ra of the main surfaces are each 0.11 nm or less. Also, in surface unevenness of the main surfaces, an average area of regions occupied by a plurality of protrusions having a height of 0.1 [nm] or more from an average plane of the surface unevenness is 25 [nm.sup.2/protrusion] or less. The arithmetic average roughness Ra and the surface unevenness are measured using an atomic force microscope with a probe having a probe tip provided with a carbon nanofiber rod-shaped member.

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.

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.

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.

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 ΔW in thickness per spacer that is calculated from a change in the thickness of the laminate due to the release of pressure is 30 μm or less.

Magnetic media including a magnetic recording layer structure formed of alternating magnetic recording sublayers and non-magnetic exchange control sublayers. The magnetic recording layer structure may include at least one magnetic recording sublayer formed to include a pair of thin films, with the films having different concentrations of platinum, ruthenium, and/or oxide segregants. That is, the sublayer has a “dual layer” structure. The dual layer structure can provide a gradient in magnetic anisotropy, saturation magnetization, and/or intergranular magnetic exchange coupling across the sublayer. In some examples, the film nearer to the substrate of the magnetic media has a higher platinum concentration than the other film. In one aspect, the magnetic media includes the substrate and the magnetic recording layer structure on the substrate, with the structure including six magnetic recording sublayers. In another aspect, a method of fabricating magnetic media with such structures is provided.

An aluminum alloy substrate for magnetic disks, including an aluminum alloy containing: 1.0 to 6.5 mass % of Mg; and the balance consisting of Al and unavoidable impurities, in which the distribution of Si—K—O-based particles with a longest diameter of 1 μm or more adhering to the surface from the surrounding environment is equal to or less than one particle/6,000 mm.sup.2; and in which the distribution of Ti—B-based particles with a longest diameter of 1 μm or more present on the surface is equal to or less than one particle/6,000 mm.sup.2, and a magnetic disk using the aluminum alloy substrate for magnetic disks.

A disk for a magnetic recording apparatus is described. The disk includes a first surface extending along a first plane, a second surface extending along a second plane parallel to the first plane, and a disk thickness between the first surface and the second surface, measured along a first direction substantially normal to the first surface. The disk further includes an edge surface disposed along a perimeter of the disk and between the first surface and the second surface, where the edge surface extends along a third plane substantially perpendicular to the first surface, a first chamfer disposed between the first surface and the edge surface, and a second chamfer disposed between the second surface and the edge surface. In an aspect, a length of the edge surface measured along the first direction may be between 40% and 80% of the disk thickness.

Disks for use in hard disk drives (HDD) or other magnetic recording apparatus. The disks are configured based on a finding that internal stress within a disk can make the disk more resistant to shock forces. In one example, a disk is provided that has a substrate with a thickness of no more than 0.5 millimeters and an internal stress no less than 300 megapascals. The relatively high internal stress within the substrate of the disk serves to reduce the magnitude of deflections caused by mechanical shocks to an HDD in which the disk is installed, as compared to other disks of equal thickness but with relatively less internal stress. Multi-platter stacks of the disks are described. Methods are also described for fabricating such disks and for rejecting disks that do not meet certain internal stress-based criteria. Substrates are also described.

A disk for a magnetic recording apparatus is described. The disk includes a first surface extending along a first plane, a second surface extending along a second plane parallel to the first plane, and a disk thickness between the first surface and the second surface, measured along a first direction substantially normal to the first surface. The disk further includes an edge surface disposed along a perimeter of the disk and between the first surface and the second surface, where the edge surface extends along a third plane substantially perpendicular to the first surface, a first chamfer disposed between the first surface and the edge surface, and a second chamfer disposed between the second surface and the edge surface. In an aspect, a length of the edge surface measured along the first direction may be between 40% and 80% of the disk thickness.