Abstract: A process for preparing cobalt-modified ferromagnetic iron oxide by modifying ferromagnetic .gamma.-Fe.sub.2 O.sub.3 particles with cobalt, wherein prior to cobalt modification treatment, the ferromagnetic .gamma.-Fe.sub.2 O.sub.3 is heat treated at a temperature in the range of from about -200.degree. C. to +30.degree. C. of the critical temperature at which partial transition of .gamma.-Fe.sub.2 O.sub.3 into .alpha.-Fe.sub.2 O.sub.3 occurs and which reduces the saturation magnetization to 99% of the saturation magnetization measured before the heat treatment, and the atomic ratio of Fe.sup.++ /Fe.sup.+++ after the cobalt modification is 0.00 to 0.10.

Abstract: A method for preparing a magnetic recording medium is described, comprising (1) pre-dispersing ferromagnetic particles having an S.sub.BET specific surface area of 35 m.sup.2 /g or more and having an adjusted water content of 0.8 wt % or more with a binder, (2) adding an additional binder and a lubricating agent thereinto, mixing and dispersing them to prepare a diserpsion of a magnetic coating composition, and (3) coating the resulting dispersion of a magnetic coating composition on a non-magnetic support.

Abstract: A magnetic recording medium which comprises a non-magnetic support having thereon a magnetic layer containing plate-shaped magnetic particles which have axes of easy magnetization perpendicular to their respective plate planes dispersed in a binder, the magnetic particles each having a multiple magnetic domain structure and having a particle diameter equal to or longer than the recorded effective shortest wavelength.

Abstract: A magnetic recording medium which comprises a non-magnetic support having thereon two or more magnetic layers comprising magnetic particles in a binder. The magnetic layer(s) other than the topmost layer comprises needle-shaped magnetic particles. The topmost layer comprises plate-shaped magnetic particles which have axes of easy magnetization perpendicular to the individual plate planes and the plate planes are oriented substantially parallel to the surface of the magnetic layer.

Abstract: This invention relates to a magnetic recording medium comprising a ferromagnetic metal thin film as a magnetic recording layer on a non-magnetic flexible support, in which the surface roughness of the support is 0.10 .mu.m or less and the period of the surface roughness is v/10.sup.6 .mu.m or less where v represents a relative speed between a magnetic head and magnetic recording medium by .mu.m/sec. In the case of providing an undercoated layer between the magnetic recording layer and non-magnetic flexible support, the surface roughness of the undercoated layer is adjusted to 0.10 .mu.m or less and the period of the surface roughness is adjusted to v/10.sup.6 .mu.m or less.

Abstract: In a process for producing a ferromagnetic powder having a high coercive force which comprises adding an aqueous solution containing Co.sup.+2 ions, or both Co.sup.+2 ions and another cation(s), and an alkali solution to a suspension of a ferromagnetic iron oxide containing the metal(s) given by these ion(s), the improvement wherein said ferromagnetic iron oxide is treated with a reducing agent prior to the preparation of the suspension.

Abstract: This invention relates to a magnetic recording medium comprising a ferromagnetic metal thin film as a magnetic recording layer on a non-magnetic flexible support, in which the surface roughness of the support is 0.10 .mu.m or less and the period of the surface roughness is v/10.sup.6 .mu.m or less where v represents a relative speed between a magnetic head and magnetic recording medium by .mu.m/sec. In the case of providing an undercoated layer between the magnetic recording layer and non-magnetic flexible support, the surface roughness of the undercoated layer is adjusted to 0.10 .mu.m or less and the period of the surface roughness is adjusted to v/10.sup.6 .mu.m or less.

Abstract: This invention relates to a method of forming a metallic thin film on a plastic substrate by electroless plating, which comprises providing an undercoated layer consisting essentially of polyvinylidene chloride or vinylidene chloride copolymer on the surface of the plastic substrate and then subjecting to a surface activating treatment and electroless plating.

Abstract: In a process for producing ferromagnetic powder which comprises adding an aqueous solution containing Co.sup.+2 ions, with or without another cation or cations, and an alkali solution to a suspension of ferromagnetic iron oxide, and heating the mixture to produce ferromagnetic iron oxide containing the metal provided by such an ion (s), the improvement wherein the heating is carried out in the presence of an oxidizing agent.

Abstract: Co- and Fe-containing ferromagnetic iron oxide powder having a high coercive force and improved stability to heat and pressure is produced by adding an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions, and an aqueous solution containing not more than 1 equivalent, based on the Co.sup.+2 ions, of Fe.sup.+3 ions to a suspension of a ferromagnetic iron oxide, and heating the mixture at a temperature of at least about 80.degree. C, preferably 90.degree. to 105.degree. C. The ferromagnetic iron oxide powder is especially suitable for producing magnetic recording media.

Abstract: A Co- and Fe-containing ferromagnetic iron oxide powder having a high coercive force and improved stability to heat and pressure is produced by adding an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions, and an aqueous solution containing not more than 1 equivalent, based on the Co.sup.+2 ions, of Fe ions to a suspension of ferromagnetic iron oxide, and heating the mixture at a temperature of at least 80.degree. C in the presence of an oxidizing agent. The ferromagnetic iron oxide powder is especially suitable for producing magnetic recording media.

Abstract: Ferromagnetic particles having a high squareness ratio, high coercivities, and stable magnetic properties are prepared by electrolyzing ferromagnetic particles in an aqueous electrolyte using a cathode carrying ferromagnetic particles. The ferromagnetic particles thus treated may be then subjected to a heat treatment, if desired. When the ferromagnetic particles are iron oxide particles, the aqueous electrolyte contains a compound of a transition element.