Magnetic transformation of Zn‑substituted Ni–Co ferrite nanoparticles

Abstract

A series of ferrite samples with the compositional formula, Ni0.2ZnxCo0.8−xFe2O4 (x = 0.0, 0.2, 0.4, 0.6 and 0.8), was prepared using the citrate-based sol–gel method for the better understanding of zinc doping on the structural and magnetic properties. X-ray diffraction (XRD) studies of the samples showed single-phase ferrite cubic structure without any secondary phases, with the average crystallite size D = 103–130 nm for the samples heat-treated at 950 °C. TEM micrograph shows nearly sphere-shaped particles with particle size consistent with the XRD results. The lattice parameter increased linearly with increasing Zn2+ ion content. Fourier transform infrared (FT-IR) measurements also confirm the formation of the cubic spinel structure of ferrite. The ferrite samples were observed by scanning electron microscopy (SEM) to be spherical nanoparticles. The surface morphology and stoichiometric ratio of the compositional elements were analyzed by scanning electron microscopy equipped with energy-dispersive spectroscopy (EDS). EDS showed that the elemental ratios were stoichiometric. The static magnetism of the magnetometer was studied by using a vibrating sample magnetometer (VSM). An examination of the magnetic properties revealed an increase in saturation magnetization with increasing Zn concentration up to x = 0.2 and a decrease thereafter. These results could be explained using Neel’s collinear two-sub-lattice model and three-sub-lattice non-collinear model suggested by Yafet and Kittel. The magnetic cubic anisotropy constant determined by the law of approach to saturation decreased with increasing Zn content. For Zn-substituted Ni–Co ferrites, the magnetic properties decrease obviously with the increase in Zn2+ ion content. This rapid decrease in magnetic properties reveals that the magnetic properties of Zn-substituted nickel–cobalt ferrite have realized the transition from hard magnetism to soft magnetism. The smaller coercivity value confirms that soft ferrite has been obtained. Meanwhile, this transition from hard magnetism to soft magnetism can be used as a potential high-frequency soft magnetic material.