Effect of heat treatment on structural and magnetic properties of Li–Ni ferrite prepared via sol–gel auto-combustion method

Nanocrystalline Li_0.35Ni_0.3Fe_2.35O₄ ferrites were prepared at different annealing temperatures by sol–gel auto-combustion method. The effects of the annealing temperature on the structure and magnetic properties of the synthesized Li–Ni ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy, Fourier transform infrared spectra and Vibrating Sample Magnetometer, and X-ray photoelectron spectrometer. Rietveld refinement of the XRD data confirmed the occurrence of phase transition from α-spinel to β-spinel, from which the ideal cation occupation and lattice parameter can be obtained. The grain size increased significantly with annealing temperature. The variation of saturation magnetization can be well explained in terms of the occupation of ions in tetrahedron and octahedron. The coercivity initially increased and later decreased significantly from 115 to 37 Oe with the increase of annealed temperature which could be attributed the fact that the 600 °C-annealed grain size is close to transition size from single- to multi-domain region.