Mossbauer, Raman and X-ray diffraction studies of superparamagnetic NiFe2O4 nanoparticles prepared by sol-gel auto-combustion method

Superparamagnetic nickel ferrite single phase nanoparticles with the average crystallite size of similar to 9 nm have been synthesized at a low temperature (220 degrees C) by the sol-gel auto-combustion method. In the present study the as prepared powder was further calcined at different temperatures for 4 h, resulting in nanoparticles of larger size. The nanoparticles exhibited superparamagnetic behavior and changes in cation distribution as revealed by the Mossbauer, Raman and X-ray diffraction studies. The Mossbauer spectra collected at 5 K and under 5 T applied magnetic field showed mixed spinel structure and canted spin order for the nanoparticles, whereas there is collinear spin order with inverse spinel structure for larger particles. The vibrational spectra of the nanoparticles showed a redshift and broadening in the Raman line shape due to confinement effects. (C) 2011 Elsevier B.V. All rights reserved.