The Influence Of Heat-treatment Temperature And Atmosphere On Cation Distribution In Ni-Zn Ferrite Prepared By Coprecipitation

Ferrites are a broad class important magnetic oxides, which are used in electronic information, automation and other fields.We researched the influence of heat-treatment temperature and atmosphere on phase structure and magnetism of spinel ferrites Ni_0.15Zn_xFe_2.85-xO₄ and Ni_xFe_3-xO₄, which were prepared by coprecipitation, It is found thatα-Fe₂O₃ second phase will be formed, when Fe ion content is more than 2.2/molecule in the samples with heat treatment in air, or in argon atmosphere of the tube furnace when the time excluding air isn't enough long before heat treatment. However, no second phase containing Ni and Zn is found in the samples. It suggestes that the conditions of Fe²+ ions entering spinel lattice are no oxygen and a higher energy than Ni²+and Zn²+ ions. We have estimated the cation distribution of all single-phase samples, and fit the dependences of saturation magnetic moment on Ni and Zn content, using Tang et al's Quantum-mechanical method for estimating ion distributions in spinel ferrites.The crystal structures of the materials at room temperature have been investigated using X'pert Pro X-ray diffraction (XRD). The magnetic properties of the samples have been measured by a Quantum Design physical property measurement system(PPMS).We calculated the phase contents in the composite Ni_0.15Zn_xFe_2.85-x-2zO_4-8z/3/(α-Fe₂O₃)z, by Rietveld fitting of the X-ray powder diffraction data, and researched the influence of the cation content in the spinel phase on the saturation magnetization at room temperature. It is found that there is threshold of Fe ion content (about 2.2/molecule) in the samples with different heat treatment in air, the excrescent Fe ions formα-Fe₂O₃ second phase, resulted from the large effective ionic radius and magnetic moment of Fe²+ ion.For the samples Ni_0.15Zn_xFe_2.85-xO₄ (x=0.16, 0.23, 0.40, 0.70å’Œ0.85),it is found that the magnetizations decrease with increasing temperature, which slope increases with increasing the Zn content. For the sample with x=0.40, the magnetization decreases to 86% of its maximal value, when the temperature is up to 380 K;,however, for the sample x=0.85, the magnetization decreases to 8% of its maximal value, when the temperature is up to 380 K.For the samples with nominal composition Ni_xFe_3-xO₄ prepared by heat treatment in the tube furnace with argon atmosphere, the content of theα-Fe₂O₃ second phase decreases with increasing the time (20, 30, 40 min, respectively) excluding air before heat treatment, and with increasing Ni content.The sigle spinel phase materials Ni_xFe_3-xO₄(x=0.00, 0.08, 0.15, 0.25, 0.35) have been obtained by heat treatment at 1573 K in argon atmosphere after excluding air for 40 min. Finally, we studied the cation distribution of single-phase samples Ni_xFe_3-xO₄ and Ni_0.15Zn_xFe_2.85-xO₄ using quantum-mechanical method for estimating ion distributions in spinel ferrites proposed by Tang et al, It is found that the theoretical saturation magnetic moment is consistent with that of experimental value well, which explains the different dependences of the saturation magnetization on doped level with Ni and Zn.