超微粒子Me_1-xZn_xFe₂O₄ (ME=Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺)の生成と磁気特性

抄録

The morphology and magnetic properties of ultrafine Me_1-xZn_xFe₂O₄ particles (Me=Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺) prepared by a chemical coprecipitation with no subsequent heating method have been explored. The X-ray diffraction data and TEM observations indicate that cubic-structured spinel particles are formed in granular shape in the entire region of Zn2+ concentration for every case only except for a case at X=0 of Me=Ni²⁺. An incremental linear relation between the lattice parameter and Zn²⁺ concentration is also observed for Me=Co²⁺, Ni²⁺ and Cu²⁺, but not for Me=Mn²⁺ with no simple relations, while the crystallite size (D₃₁₁) obtained from X-ray line broadening, which is consistent with TEM observations as well, decreases with the higher Zn²⁺ concentration for all cases, nevertheless the coercivity (1Hc) decreases, in other words the magnetic property is softened as is verified with mossbauer measurements.
Although the trend in enhanced variation of the saturation magnetization with Zn²⁺ contents is similar to one for bulk materials for X=0-0.6 regions, the values are always small compared to bulk values, for more than X=0.6 the effect of high magnetic moment of ultrafine ZnFe₂O₄ plays a role. To interpret the low magnetization, by assuming a core model and a presence of magnetically inactive surface layer in a particle, the thickness of the layer is obtained for each sample. A correlation of the larger thickness with the larger magnetical softness of the relevant materials has been suggested.