Characteristics of cobalt adsorbed iron oxide tapes

The new magnetic material, "cobalt adsorbed" iron oxide, is an acicular single domain particle developed for high density magnetic recording media. The several magnetic instabilities of conventional cobalt doped or modified iron oxide are improved in this material. The structure of this material is quite different from the others. Generally, the particle for magnetic recording media is uniform in its structure from the surface to the inner part but this is a heterogeneous one, i.e, the inner part is pure iron oxide and the surface part is a high cobalt content structure formed by adsorbed cobalt ion. The surface anisotropy due to the adsorbed cobalt ion is in the order of 10
⁶
erg/cm
³
. This surface anisotropy is uniaxial and its direction coinsides with that of the shape anisotropy of the acicular particle. The temperature coefficient of coercivity is as small as that of pure gamma ferric oxide. The new magnetic recording tapes are developed using this cobalt adsorbed iron oxide particles for both the home video tape and the audio cassette tape used in the high bias position. The home video tape is superior in color S/N and maximum output level than conventional one. The audio cassette tape is superior in sensitivity, in maximum output level, and in frequency response at high input level than conventional tapes.