A glass for magnetic recording medium substrate is an amorphous oxide glass. In terms of mol %, SiO.sub.2 content ranges from 45 to 68%, Al.sub.2O.sub.3 from 5 to 20%, total content of SiO.sub.2 and Al.sub.2O.sub.3 60 to 80%, B.sub.2O.sub.3 from 0 to 5%, MgO from 3 to 28%, CaO from 0 to 18%, total content of BaO and SrO 0 to 2%, total content of alkali earth metal oxides from 12 to 30%, total content of alkali metal oxides from 3.5 to 15%, and at least one kind selected from the group made of Sn oxide and Ce oxide being included, a total content of Sn oxide and Ce oxide ranges from 0.05 to 2.00%, a glass transition temperature ≥625° C., a Young's modulus ≥83 GPa, a specific gravity ≤2.85, and an average linear expansion coefficient at 100 to 300° C.≥48×10.sup.−7/° C.

Large magnetic moment compositions are formed by stabilizing ternary or other alloys with a epitaxial control layer. Compositions that are unstable in bulk specimen are thus stabilized and exhibit magnetic moments that are greater that a Slater-Pauling limit. In one example, Fe.sub.xCo.sub.yMn.sub.z layers are produced on an MgO(001) substrate with an MgO surface serving to control the structure of the Fe.sub.xCo.sub.yMn.sub.z layers. Magnetizations greater than 3 Bohr magnetons are produced.

The magnetic recording medium includes a long substrate body, and a magnetic layer including a powder of cubic crystal ferrite magnetic particles. The sum of a squareness ratio in the longitudinal direction and a squareness ratio in the vertical direction is 1.2 or more, and the difference of the squareness ratio in the longitudinal direction and the squareness ratio in the vertical direction is 0.15 or more.

An object is to provide a magnetic recording medium having excellent traveling stability and a thin total thickness.

The present technology provides a tape-shaped magnetic recording medium including: a magnetic layer; an underlayer; a base layer; and a back layer, in which a surface on a side of the magnetic layer has a kurtosis of 3.0 or more, a surface on a side of the back layer has a kurtosis of 2.0 or more, the surface on the magnetic layer side has arithmetic average roughness R.sub.a of 2.5 nm or less, the base layer includes a polyester as a main component, the magnetic recording medium has an average thickness t.sub.T of 5.6 μm or less, the magnetic recording medium includes a lubricant, the lubricant includes a fatty acid and a fatty acid ester, and a mass ratio between the fatty acid and the fatty acid ester extracted with hexane satisfies fatty acid/fatty acid ester ≤0.6, and the magnetic recording medium has pores, and the pores have an average diameter of 6 nm or more and 11 nm or less when the diameters of the pores are measured in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried.

A method for manufacturing the ring-shaped glass spacer to be arranged in contact with a magnetic disk in a hard disk drive apparatus, including: preparing a ring-shaped glass blank; and grinding main surfaces of the ring-shaped glass blank by using grinding pads that include diamond particles as fixed abrasive particles.

The present disclosure relates to magnetic recording disks having a magnetic recording layer that includes a plurality of three-dimensional segregant structures. Each three-dimensional segregant structure extends from a first radius of the recording disk to a second radius of the recording disk, and each three-dimensional segregant structure is made of a first segregant material. The magnetic recording layer also includes a plurality of magnetic grains between adjacent three-dimensional segregant structures, and a second segregant material between adjacent magnetic grains. The present disclosure also relates to corresponding methods of manufacturing such a magnetic recording layer.

The magnetic tape includes a non-magnetic support, a magnetic layer that includes ferromagnetic powder having an average particle volume of 2,500 nm.sup.3 or less on one surface side of the non-magnetic support, and a back coating layer that includes non-magnetic powder on the other surface side of the non-magnetic support, in which the ferromagnetic powder is ferromagnetic powder selected from the group consisting of hexagonal ferrite powder and ε-iron oxide powder, and a ratio (PSD.sub.5μm-PSDmag/PSD.sub.10μm-PSDbc) of the magnetic layer and the back coating layer is in a range of 0.0050 to 0.20. A magnetic tape cartridge and a magnetic recording and reproducing apparatus include the magnetic tape.

Magnetic powder includes: an epsilon-phase iron oxide-based compound selected from ε-Fe.sub.2O.sub.3 or a compound represented by Formula (1). The magnetic powder has an average particle diameter of 8 nm to 25 nm, a ratio of Hc to Hc′ of from 0.6 to 1.0, and Hc′ satisfying Expression (II). Hc′ represents a magnetic field at which a value of Expression (I) becomes zero in a magnetic field-magnetization curve obtained by performing measurement at a maximum applied magnetic field of 359 kA/m, a temperature of 296 K, and a magnetic field sweeping speed of 1.994 kA/m/s. M represents magnetization and H represents applied magnetic field. Hc represents a magnetic field at which magnetization becomes zero in the magnetic field-magnetization curve. In Formula (1), A represents at least one metal element other than Fe, and a represents a number that satisfies a relationship of 0<a<2.
d.sup.2M/dH.sup.2  Expression (I)
119 kA/m<Hc′<2380 kA/m  Expression (II)
ε-A.sub.aFe.sub.2-aO.sub.3  (1)

A film-forming apparatus and a method for manufacturing a magnetic recording medium are provided. The film-forming apparatus includes a rotating body which moves a base material with a strip shape which has flexibility, a plurality of cathodes which are provided to oppose a rotating surface of the rotating body; and a plurality of accommodating sections which accommodate each of the plurality of cathodes. The method includes sequentially film-forming a plurality of thin films on a base material using a plurality of cathodes which are provided on a moving path of the base material while moving the base material with a strip shape which has flexibility. Each of the plurality of cathodes is accommodated in a plurality of accommodating sections.

A film-forming apparatus and a method for manufacturing a magnetic recording medium are provided. The film-forming apparatus includes a rotating body which moves a base material with a strip shape which has flexibility, a plurality of cathodes which are provided to oppose a rotating surface of the rotating body; and a plurality of accommodating sections which accommodate each of the plurality of cathodes. The method includes sequentially film-forming a plurality of thin films on a base material using a plurality of cathodes which are provided on a moving path of the base material while moving the base material with a strip shape which has flexibility. Each of the plurality of cathodes is accommodated in a plurality of accommodating sections.