Correlation of crystal structure and magnetic properties of Co(1-x)NixFe2O4/SiO2 nanocomposites

The Co((1-x))NixFe2O4/SiO2 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) nanocomposites were prepared using the sol-gel method and characterized by Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray Spectroscopy (EDX) and magnetic measurements. Moreover, Mossbauer spectroscopy (performed at room temperature and at 4.2 K with applied field 6 T) was performed to determine the cation distribution within the spinel network. The PXRD measurements confirmed the presence of the spinel phase in all samples. The particle diameters, obtained from the PXRD, were found out to vary between 15 and 24 nm. The lattice parameters decrease linearly with increasing content of the Ni2+ ions. The ZFC (zero field cooled) and FC (field cooled) measurements of the magnetization showed that the blocking temperature is well above the room temperature for all samples. Both the coercivity and the saturation magnetization decrease linearly with increasing content of the Ni2+ ions. The room temperature Mossbauer spectra exhibit a sextet with asymmetric lines indicating a different crystal environment for the Fe3+ ions, accommodated in the tetrahedral and octahedral sites. By application of the external magnetic field at 4.2 K, these overlapped sextets split up allowing determination of the ratio of the Fe3+(O-h)/Fe3+(T-d) that exhibited slight decrease with increasing Ni content. The obtained results are discussed considering influence of the Ni doping. (C) 2013 Elsevier B.V. All rights reserved.