Size variation and magnetic dilution effects on the structure and magnetic properties of cobalt zinc ferrite

Nanocrystalline cobalt zinc ferrites Co 1− x Zn x Fe 2 O 4 ( x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0), have been prepared by employing a precursor combustion method via decomposition of the metal carboxylato hydrazinate precursors. This synthesis technique yields nanoparticles with particle size between 12 and 15 nm as determined from transmission electron microscopy (TEM) studies. The nanoferrites were then sintered at 1000 °C for 15 h to obtain micrometer size ‘bulk’ ferrites in the range of 0.3–0.8 μm. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy confirmed the formation of the mixed ferrites without any impurities. Addition of non-magnetic ion like Zn 2+ into the crystal structure of cobalt ferrite leads to a prominent change in the size, structure and properties. The saturation magnetization values ( M S ) increases upto x = 0.4 and then decreases with further increase in Zn concentration. A maximum M S value of 90.85 emu/g and 79.59 emu/g for x = 0.4 was obtained for the sintered and nanoferrite sample, respectively. The lower M S and higher coercivity ( H C ) values for nanoferrites than the sintered ferrites exhibited a strong dependence on the particle size due to the cation distribution and surface effects. The Curie temperature ( T C ) was found to decrease appreciably with the reduction in particle size and with increasing concentration of Zn. The room temperature Mössbauer spectra showed a transition from ferrimagnetic to a paramagnetic state with increasing zinc concentration along with superparamagnetic features which was in corroboration with VSM studies.