Structural and magnetic properties of Ni1−xZnxFe2O4 (x=0, 0.5 and 1) nanopowders prepared by sol–gel method

Abstract

A series of nanostructured Ni–Zn ferrites Ni1−xZnxFe2O4 (x=0, 0.5 and 1) with a grain size from 24 to 65nm have been prepared with a sol–gel method. The effect of composition and sintering temperature on morphology, magnetic properties, Curie temperature, specific heating rate at 295kHz and hysteresis loss have been studied. The highest coercivity of 50 and 40Oe, were obtained for NiFe2O4 and Ni0.5Zn0.5Fe2O4 samples with the grain size of 35 and 29nm, respectively. The coercivity of Ni and Ni–Zn mixed ferrites decreased with temperature. The Bloch exponent was 1.5 for all samples. As the grain size increased, the Curie temperature of NiFe2O4 increased from 849 to 859K. The highest saturation magnetization of 70emu/g at 298K and the highest specific heating rate of 1.6K/s under radiofrequency heating at 295kHz were observed over NiFe2O4 calcined at 1073K. Both the magnitude of the hysteresis loss and the temperature dependence of the loss are influenced by the sintering temperature and composition.