Magnetic properties of Ni-Zn ferrite powders formed by self-propagating high temperature synthesis reaction

Abstract

The ferrite compositions of Ni_xZn_xFe₂O₄ were synthesized by self-propagating high temperature synthesis reaction with various contents of iron, iron oxide, nickel oxide and zinc oxide at oxygen partial pressures varying between 0.05 to 5.0 MPa. The oxygen pressure promoted the combustion reaction, while the compacting pressure retarded the reaction. The rate equation of ferrite formation is shown to be v = 14.5 exp (T_c1380 - 1) P ^0.2_O2 . Phase identification of the final products by X-ray diffraction (XRD) revealed that the enhanced combustion reaction with oxygen pressure and iron content in the reactants resulted in increasing the spinel content in the combustion product. As the oxygen pressure changed from 0.1 to 5 MPa, the coercive force and residual magnetization decreased by about 73% and 66%, respectively, whereas, the maximum magnetization, susceptibility and Curie temperature increased by about 70%, 60%, and 32%, respectively. The improved magnetic properties are accounted for by the enhanced iron oxidation at a given combustion condition. Compared to the magnetic properties and productivity of the Ni-Zn ferrites prepared by wet chemical method, the self-propagating high temperature synthesis method at high oxygen pressure is one of the useful methods to fabricate improved ferrite powders.