Hitachi Maxell, Limited

Susumu Kitaoka

Haruo Andoh

Junichi Hirata

Akira Kato

Toshinobu Sueyoshi

Hikaru Ishida

Cobalt-containing iron oxide magnetic particles having a high coercive force and a small surface electrical resistance which are useful as a recording element for a magnetic recording medium, and a method for the preparation of the same comprising reducing acicular .gamma.-Fe.sub.2 O.sub.3 particles in a reducing gas or liquid until the iron oxide reaches an intermediate oxidation state between .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, dispersing the resulting iron oxide particles into an aqueous solution containing a cobalt salt and optionally a ferrous salt and an alkali of one equivalent or more to the metal salt(s), and heating the mixture at a temperature of higher than room temperature up to a boiling point of the mixture under an atmospheric condition such that the divalent iron is substantially not oxidized. The cobalt is thereby predominantly incorporated into the most outer layer of the acicular iron oxide particles.

Cobalt-containing iron oxide magnetic particles and method for the

Method for preparing cobalt-containing iron oxide magnetic particles

An improved magnetic recording medium is disclosed, particularly a magnetic tape suitable for sound recording and video recording, which comprises as a recording element a mixture of cobalt-containing iron oxide magnetic particles consisting essentially of ferromagnetic iron oxide particles containing cobalt and optionally a divalent iron in the most outer layer thereof, and .gamma.-ferric oxide particles in the ratio of 10:90 to 50:50 by weight, said mixture of cobalt-containing iron oxide magnetic particles and .gamma.-ferric oxide particles being applied to a substrate (e.g. a polyester film) with a binding agent. The magnetic recording medium has excellent electromagnetic transducing properties and improved charging properties and is useful for conventional magnetic recording apparatus used at normal position with high sensitivity in wide range of frequency.

Magnetic recording medium

Growing community of inventors

Kyoto, Japan

Susumu Kitaoka