Formation and magnetic properties of γ-Fe2O3particles surface modified with crystallized cobalt-ferrite |
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Authors: | Amemiya M. Kishimoto M. Hayama F. |
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Affiliation: | Hitachi Maxell, Ltd., Koizumi, Otokuni, Oyamazaki, Kyoto, Japan; |
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Abstract: | Acicular γ-Fe2O3particles were heated at 90°C in alkali solution containing Co2+and Fe2+with Co2+/Fe2+ratio of 0.5. The coercivity of resultant particles increased linearly with increasing the Co2+content, and the coercivity of 900 Oe was obtained for the particles with Co2+content of 7 wt%. The shape of the particles is acicular, and an appreciable variation of morphology by the treatment in alkali solution was not observed. Cobalt-ferrite was expected to crystallize epitaxially on the surface of γ-Fe2O3particles, and the increase of coercivity was attributed to the magnetic anisotropy of the cobalt-ferrite. A variation of coercivity by annealing at 60°C and print-through were small compared with those of the particles in which iron were homogeneously substituted by cobalt ions. Such stability was explained by considering that a very high concentration of cobalt ions exist only on the surface of γ-Fe2O3particles, and the migration of cobalt ions is extremely difficult. |
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