Investigation of Ferrimagnetic Cobalt-Doped Gamma-Ferric Oxide Micropowders

Abstract

The magnetic properties of cobalt‐doped γ‐Fe2O3 were investigated, and the crystallographic properties were examined using the Mössbauer technique and x‐ray diffraction. An increase in lattice parameter with cobalt concentration was observed. A large increase in coercive force, especially pronounced at low temperatures, was proportional to cobalt concentration, and may be accounted for by single‐ion anisotropy. The magnetic moment changed very little. Measurements on partially aligned particles indicated that the particles were single domain. The Mössbauer spectra provided no evidence for the presence of Fe2+ or Fe4+ions. Also, at helium temperature the anisotropy was such that the samples were not saturated at 50 kOe. The experimental data are consistent with the hypothesis that the cobaltions replace iron on B sites and also fill B‐site vacancies. Conversion to α‐Fe2O3 on heating was never attained completely, and it is proposed that cobalt ferrite is present in the heated samples.