Effect of vanadium doping on structural and magnetic properties of defective nano-nickel ferrite

Nano-nickel ferrites defected by vanadium doping (NiVxFe2-1.67xO4, 0 <= x <= 0.25) were prepared using a simple sol gel method. Rietveld analysis revealed a nonmonotonic change in lattice parameter, oxygen parameter and magnetization upon doping with vanadium. Cation distributions suggested from either Rietveld analysis or from experimental magnetic moments were in a good agreement. For low doping values (x = 0.05), vanadium was residing mainly in octahedral sites, while for samples with vanadium content (x >= 0.1) a significant part of vanadium ions resided at tetrahedral sites; a result which has been confirmed by the analysis of Fourier-transform infrared (FTIR) spectrums obtained for the samples. The transmission electron microscope (TEM) image showed fine spherical particles with size of similar to 11 nm. All samples showed a superparamagnetic nature with a nonmonotonic change of either magnetization (M-S) or coercivity (H-C) with the content of nonmagnetic V5+. The cation occupancies indicated presence of an enormous number of vacancies through doping with high valence cation V5+, making present samples potential electrodes for Li-or Na-ion batteries.