Static magnetic properties and cation distribution in partially inverse polycrystalline Ni–Co ferrites

Polycrystalline samples of Ni 1 − x Co x Fe 2 O 4 (where x = 0.0, 0.4, 0.5, 0.6, 1.0) have been synthesized by solid state sintering of stoichiometric nanoparticles prepared by sol–gel technique. Rietveld refined powder X-ray diffraction patterns confirm the formation of a single cubic spinel phase in each sample. Substitution of cobalt ions results in the increase of the lattice parameter. The saturation magnetization and coercivity of all the samples were measured using PPMS-VSM and found to increase from 51.6 to 82.2 emu/g, and 9.7 to 588 Oe, respectively. The observed magnetic ordering is explained on the bases of two sublattice model and redistribution of cations in these partially inverse Co substituted Ni ferrite samples. The strong increment (60 times) in the coercivity is explained on the bases of microstructure and magnetocrystalline anisotropy. Cation redistribution in these samples is proposed on the basis of the observed magnetic moment. Close matching of lattice parameter calculated from the magnetic data and estimated from the X-ray diffraction data supports the proposed cation redistribution in the partially inverse spinel phase of NCFO.