Characterization and magnetic properties of cobalt ferrite nanoparticles

Abstract

Inverse spinel cobalt ferrite (CoFe2O4) nanoparticles were synthesized by a polymer pyrolysis method and calcined at various temperatures from 800 to 1000 °C. The structure, morphology, valence states and magnetic properties of the calcined samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES) and vibrating sample magnetometer (VSM). All calcined samples had the cubic spinel type structure with average crystallite sizes increasing from 80 ± 2 to 100 ± 3 nm with increasing calcination temperature. The XANES spectra allowed the valence states of the Fe3+ and Co2+ ions in the samples to be established and simulation of the XANES spectra suggested that the site occupancy of Fe3+ and Co2+ ions was mixed, with the majority of Co2+ ions occupying octahedral sites and the majority of Fe3+ ions occupying tetrahedral sites within the spinel structure. All samples exhibited ferromagnetic behavior at room temperature with a maximum saturation magnetization (MS) of 3.42 μB and a coercivity (HC) of 1100 Oe for crystallite sizes of 100 nm. The origin of the ferromagnetism is discussed in relation to the distribution of Fe3+ and Co2+ ions within the lattice and the crystallite sizes.