Influence of size and magnetocrystalline anisotropy on spin canting anomaly in fine ferrimagnetic particles

Fine equiaxed γ-Co_xFe_2-xO₃ (x=0, 0.06) particles with a diameter ranging from 200 to 1000 Å were prepared by chemical precipitation. The average crystallite sizes were determined from x-ray line broadening measurements. The saturation magnetization and magnetocrystalline anisotropy of the particles were determined by using the approach to saturation. An empirical linear dependence of the specific saturation magnetization σ_s on the specific surface area S _a of the fine crystallites was obtained in the form of σ_s(S)=σ_s(∞)(1-AS_a). The slope A which reflects the surface spin canting anomaly is different for γ-Fe₂O₃ and γ-Co_0.06Fe _1.94O₃ particles. Under the supposition of the fine crystallite consisting of two parts, i.e., the surface layer, whose magnetic moment cannot be turned entirely along the direction of the applied field, but makes an average canting angle with the field, and the inner part, whose magnetic moment can be aligned along the direction of the applied field, the above formula can be interpreted well. The different slope A for γ-Fe ₂O₃ and γ-Co_0.06Fe_1.94O ₃ particles may be caused by the different anisotropies of the two series particles.