Preparation and study of NiFe2O4/SiO2 core-shell nanocomposites

NiFe2O4 nanoparticles (4-32 nm) have been prepared by co-precipitation technique. They have been coated with SiO2 following the Stober process to prepare core-shell nanocomposite. The phase and average crystallite size was obtained from X-ray diffraction analysis. The particle size distributions and morphology of the core-shell nanoparticles were studied by transmission electron microscope and field emission scanning electron microscope. Fourier transform infrared spectroscopic analysis gave information about the bonds present in the coated and uncoated samples. Superparamagnetic properties were observed at room temperature when the uncoated particle size was around or less than 15 nm. The blocking temperature increases with the increase in the particle size. In superparamagnetic state, the field dependence of magnetization follows Langevin function which was originally developed for paramagnetism. (C) 2009 Elsevier B.V. All rights reserved.