Effect of annealing temperature on lattice defects, microstructure, and magnetic properties of submicron NiFe2O4 powders

Abstract Lattice defects play an important role in the tailoring of the magnetic properties of spinel ferrites. Thus, understanding the structure-property relation is essential for practical applications of these materials. In the present work, the relationship between defects, microstructure, and magnetic properties of submicron spinel nickel ferrites has been investigated. Four samples of nickel ferrites were obtained by a sol-gel method followed by annealing for 3 h at different temperatures in air atmosphere. A set of techniques, such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction along with Rietveld refinement, and Mössbauer spectroscopy, was used to characterize the particle morphology, elemental composition, crystal structure, and cation distribution, respectively. X-ray line profile analysis was used to estimate the diffraction domain size and microstrain of the obtained samples. The magnetic properties of the samples were investigated by DC magnetometry. The results showed that the lattice defects and microstrain decrease, the diffraction domain increases, and the particle morphology changes as the annealing temperature increases. Mössbauer spectroscopy data indicated a small variation in distribution of Fe cations over the tetrahedral and octahedral sites for samples annealed at 500 and 1000 $$^{\circ }$$ C. The magnetic hysteresis curves for all samples exhibited low coercivity and moderate saturation magnetization. The variation of magnetic parameters with microstructural parameters revealed that the saturation magnetization increased from 45.9 to 47.2 emu/g and coercivity decreased from 138 to 81 Oe with crystallite growth and reduction in microstrain. These results show how defects and microstructure are related to changes in magnetic properties of nickel ferrites with submicron size distribution.