Structural and Magnetic Properties of Zn and Co Substituted Nickel Ferrites Prepared by the Citrate Sol-Gel Method

Three different ferrites with nominal compositions, NiFe2O4, Ni0.50Zn0.50Fe2O4, and Ni0.50Zn0.25Co0.25 Fe2O4, were synthesized by wet chemical citrate sol-gel process, mainly to understand how doping with different cations affects the magnetic properties. X-ray diffraction (XRD) confirmed the existence of a single phase without detectable impurities. XRD analysis using the Rietveld refinement technique showed that the samples crystallize in a cubic spinel structure with the Fd-3m space group and the lattice constants were evaluated. Scanning electron microscopy of the calcined samples revealed particles that were approximately 100 nm size. The elemental analysis by energy dispersive spectroscopy showed that the element concentrations were at the stoichiometric ratio in all samples. The magnetic properties measured at room temperature using a vibrating sample magnetometer revealed enhancement in the magnetic properties of nickel ferrite when doped with zinc and cobalt. The high field regimes of the hysteresis loops were modeled using the Law of Approach to Saturation to determine the cubic anisotropy coefficient (K). The anisotropy coefficient increased with doping Zn and Co, which could be explained in terms of the site occupancy of the dopants in the cubic spinel lattice.