Hitachi Maxell, Limited

Junichi Hirata

Haruo Andoh

Susumu Kitaoka

Sadamu Kuse

Seigi Kawarai

A magnetic tape cartridge comprising a magnetic tape suitable for long time recording which has a coefficient of thermal shrinkage of 0.6% or less the coefficient being measured after the tape is wound around a hub at least 300 turns and kept at 105.degree. C. for 30 minutes.

Magnetic tape cartridge

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.

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Otokuni, Japan

Junichi Hirata