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.

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, and a difference between D95 and D5 is 3 μm or more.

A ring-shaped glass spacer is configured to be arranged in contact with a magnetic disk in a hard disk drive apparatus. A surface resistivity of a surface of a glass material of the glass spacer at 22 (° C.) is lower than a surface resistivity of an inner portion of the glass material at 22 (° C.).

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.

The present invention relates to a magnetic recording medium including a substrate; an underlayer laminated upon the substrate; and a magnetic layer laminated upon the underlayer, wherein the underlayer includes a first underlayer containing a compound represented by a following general formula: MgO.sub.(1-X), where X is within a range of 0.07 to 0.25, the magnetic layer includes a first magnetic layer containing an alloy having a L1.sub.0 structure, and the alloy having the L1.sub.0 structure includes B, and the first underlayer is in contact with the first magnetic layer.

A glass sheet composite having two or more glass sheets and a liquid layer between at least a pair of glass sheets out of the glass sheets, wherein a thickness of the liquid layer is 1/10 or less of a total thickness of the pair of glass sheets when a total thickness of the pair of glass sheets is 1 mm or less, and 100 μm or less when the total thickness of the pair of glass sheets is more than 1 mm.

A heat-assisted magnetic recording (HAMR) media stack is provided in which Iridium (Ir)-based materials may be utilized as a secondary underlayer instead of a Magnesium Oxide (MgO) underlayer utilized in conventional media stacks. Such Ir-based materials may include, e.g., pure Ir, Ir-based alloys, Ir-based compounds, as well as a granular Ir layer with segregants. The use of Ir or Ir-based materials as an underlayer provide advantages over the use of MgO as an underlayer. For example, DC sputtering can be utilized to deposit the layers of the media stack, where the deposition rate of Ir is considerably higher than that of MgO resulting in higher manufacturing production yields. Further still, less particles are generated during Ir-based layer deposition processes, and Ir-based underlayer can act as a better heat sink. Further still, the morphology and structure of a recording layer deposited on an Ir-based layer can be better controlled.

A soft underlayer (SUL) and methods for making an SUL are provided, the SUL having characteristics that make it compatible with the high temperature requirements associated with heat-assisted magnetic recording (HAMR) media growth and writing, e.g., temperatures greater than 500° C. The SUL may have a high crystallization temperature of greater than 450° C. and a high Curie temperature greater than 300° C., for example. Additionally, the SUL can maintain a saturation magnetization value greater than, e.g., 9 kGauss, at such high temperatures, thereby having the ability to remain amorphous at temperatures up to, e.g., 650° C., and exhibiting a relatively flat integrated noise profile from approximately 300° C. to 650° C. Further still, a spacer layer material is chosen such that inter-diffusion does not occur at these high temperatures.

According to one embodiment, a disk device includes a housing, a plurality of magnetic recording media disposed in the housing in a multi-layered manner with intervals therebetween and a plurality of spacer rings each disposed between each adjacent pair of the magnetic recording media. At least one of an uppermost magnetic recording medium and a lowermost magnetic recording medium includes a substrate having a rigidity higher than that of substrates of the other magnetic recording media, and spacer rings brought into contact with the magnetic recording media with the substrate having the higher rigidity have a thermal expansion coefficient different from a thermal expansion coefficient of the other spacer rings.

A substrate for a magnetic disk includes a substrate main body having two main surfaces and an outer circumferential edge surface that has a side wall surface and chamfered surfaces, and a film that is an alloy film containing Ni and P and provided on a surface of the substrate main body. A disk shape of the substrate main body has an outer diameter of 90 mm or more. A thickness T of the substrate that includes the film provided on the main surfaces is 0.520 mm or less. A total thickness D mm of the film on the main surfaces and the thickness T mm satisfy D≥0.0082/T−0.0015. A film thickness of the film on the outer circumferential edge surface is larger than a film thickness of the film on the main surfaces, and is 150% or less of the film thickness of the film on the main surfaces.