Abstract: A magnetic recording medium comprising a non-magnetic substrate and a magnetic alloy layer formed on the substrate with a non-magnetic primer layer containing chromium as the main component interposed therebetween, wherein the magnetic alloy layer contains cobalt and nickel as the main components and not more than 8 atomic % of boron and has been formed by sputtering under such a condition that a negative bias voltage is applied to the non-magnetic substrate.

Abstract: A perpendicular magnetic recording medium having a magnetic layer comprised of a metal magnetic thin film on a nonmagnetic support. The half-value width of the switching field distribution obtained from a remanent magnetization curve in the intrinsic easy direction of magnetization (axis of easy magnetization from which shape magnetic anistrophy is removed) of the magnetic layer is no more than 40 kA/m.Rectangular wave signals are recorded or reproduced on or from a Co--O type perpendicular magnetic recording medium with a direction .theta..sub.E of the axis of easy magnetization tilted in a range of 10.degree. to 45.degree. from the direction perpendicular to the plane of the film of the magnetic layer using a ring type magnetic head with a gap length Lg of not more than 0.18 .mu.m.

Abstract: The non-acicular modified maghemite and magnetite have high coercivity of, for the maghemite, up to 2200 Oe, saturation and residual magnetization of 63-85 emu/g and 43-52 emu/g, respectively; for the magnetite, the corresponding values are 800-1600 Oe, 82-87 emu/g, and 44-51 emu/g, respectively; while retaining same squareness ratio and same chemistry with conventional iron oxides, fine particle size of around 50 nm, easier dispersion and coating, invaried properties after curing, and low value of temperature coefficient of coercivity (0.24-0.37%/.degree. C. for the maghemite and 0.20-0.33%/.degree. C. for the magnetite), have been invented. They are thus especially suitable for high density recording. The modified maghemite and magnetite are prepared by precipitating from aqueous solution containing Fe, Mn, Co and Zn ions at proper ratio using an organic alkali as precipitant, followed by specific heat treatment sequences.

Abstract: An optical disk includes a pair of disk substrates and a recording layer on at least one substrate, the disk substrates being mated by bonding the substrates at their inside surfaces through an adhesive layer such that the recording layer is internally enclosed. In one form, a pair of self-adhesive layers are applied to the respective substrate inside surfaces and formed with a plurality of channels extending over the surface from the outer or inner circumferential edge to the outer circumferential edge. The self-adhesive layers are bonded together to integrate the pair of disk substrates in which the channels form passages for allowing air escape. In another form, a pair of adhesive layers are applied to the respective substrate inside surfaces. The pair of disk substrates are joined by bonding the adhesive layers together through a buffer foam sheet.

Abstract: A magnetic recording medium comprising a non-magnetic support, a magnetic layer on one surface of said non-magnetic support, a back coating layer on the other surface of said non-magnetic support and a primer layer containing acicular hexagonal ferrite magnetic powder between said non-magnetic support and at least one of said magnetic layer and said back coating layer, which is used with a video recorder fitted for high density recording and in particular, which copes with prolongation of a recording time.