Evaluation of NiFe2O4 ferrite nanocrystalline powder synthesized by a sol–gel auto-combustion method

Nanocrystalline NiFe2O4 ferrite powder was prepared by a sol–gel auto-combustion method from metal nitrates and citric acid. The combustion process is an oxidation–reduction reaction in which the NO 3 - ion is oxidant and the carboxyl group is reductant. The thermal analysis of nitrate–citrate gels and the phase evolution of as-burnt powder with the different ratios of Fe/Ni and calcined powder were investigated by DTA/TG and XRD techniques respectively. SEM and Hysteresigraph were also used to characterize the microstructure and magnetic properties of the products. The results revealed that the nitrate–citrate gel exhibits a self-propagating combustion behavior. By using this novel auto-combustion method, NiFe2O4 ferrite powder was obtained with crystallite size of 20–40 nm and suitable soft magnetic properties.