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

The ferrite compositions of NixZnxFe2O4 were synthesized by self-propagatin g high temperature synthesis reaction with various contents of iron, iron o xide, nickel oxide and zinc oxide at oxygen partial pressures varying betwe en 0.05 to 5.0 MPa. The oxygen pressure promoted the combustion reaction, w hile the compacting pressure retarded the reaction. The rate equation of fe rrite formation is shown to be nu = 14.5 exp (T-c/1380 - 1) P-O2(0.2). Phas e 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 combusti on product. As the oxygen pressure changed from 0.1 to 5 MPa, the coercive force and residual magnetization decreased by about 73% and 66%, respective ly, whereas, the maximum magnetization, susceptibility and Curie temperatur e increased by about 70%, 60%, and 32%, respectively. The improved magnetic properties are accounted for by the enhanced iron oxidation at a given com bustion condition. Compared to the magnetic properties and productivity of the Ni-Zn ferrites prepared by wet chemical method, the self-propagating hi gh temperature synthesis method at high oxygen pressure is one of the usefu l methods to fabricate improved ferrite powders.