Abstract: A ferromagnetic metal powder for a magnetic recording medium that combines good magnetic properties and oxidation stability, and a magnetic recording medium using the powder. A method of producing the magnetic powder comprises using oxygen to form an oxide film, then changing the state of the oxide film by using moderate gas phase activation treatment in an active gas, using, for example, CO or H2 or other such gas having reducing properties. ESCA-based measurements show that the binding energy peak of the powder is more to the low energy side compared to when the above treatment is not used, showing that the oxide film has oxidation resistance. The storage stability of a magnetic recording medium is improved by using the powder.

Abstract: A magnetic powder for magnetic recording medium comprises acicular particles constituted primarily of Fe, wherein the powder contains Co in an amount such that the Co/Fe ratio is 50 at. % or less and the Co is contained in a manner such that the surface portion has a higher concentration than the core portion of the particles, and upon subjecting the magnetic powder for magnetic recording medium to TG measurement, the powder exhibits at least two oxidation starting points: a low-temperature side oxidation starting point and a high-temperature side oxidation starting point. The magnetic powder achieves improved resistance to oxidation without sacrificing magnetic characteristics.

Abstract: A magnetic powder is provided composed of particles having a balanced shape and distribution, the particles having a small, uniform volume, making it possible to achieve improved density and reliability of a coating type magnetic recording medium. The magnetic powder has Fe as a main component, and is comprised of particles having a cross-section perpendicular to the particle major axis that is substantially round or elliptical, wherein a standard geometrical deviation indicating the variation in cross-sectional area thereof is within the range of 1.01 to 3.0. The invention is also directed to a magnetic powder in which the standard geometrical deviation indicating the variation in the particle volume is within the range of 1.01 to 4.0, and the standard geometrical deviation indicating variation in the flat acicularity is within 1.01 to 2.0.

Abstract: Non-magnetic powder of particles for non-magnetic lower layer applications is provided that enables a multilayer coating type magnetic recording medium having good surface smoothness to be obtained. The particles are iron compound particles having a long axis with a standard geometrical deviation, as obtained from a transmission electron microscope image, that is greater than 1.5, and a short axis with a standard geometrical deviation, as obtained from a TEM image, that is greater than 1.35. The iron compound particles may be hematite or iron oxyhydroxide.

Abstract: A nonmagnetic powder, used for the nonmagnetic layer of a coated type magnetic recording medium having a multilayer structure, has good dispersibility in the binder in which it is dispersed to prepare a coating material that is applied to the nonmagnetic layer. The nonmagnetic powder has an iron compound as its principal component and exhibits a maximum pore volume value in a pore diameter range of 0.01 ?m to 0.05 ?m within a pore diameter range of 0.0018 ?m to 0.1 ?m in which the relationship between pore diameter and pore volume is calculated by a mercury injection method. The nonmagnetic powder exhibits a cumulative pore volume value in a pore diameter range of 0.0018 ?m to 0.01 ?m that is not more than 30% of the cumulative pore volume value in the pore diameter range of 0.0018 ?m to 0.1 ?m.