Structural and magnetic properties of FexOy nanoparticles dispersed in silica matrix

Some FexOy-SiO2 composites were prepared by the colloidal and alkoxidic route of the sol-gel method. The dried gels were thermally treated and the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorption (IR) spectroscopy, magnetic susceptibility measurements and Mossbauer spectroscopy. Nanoparticles of gamma and /or alpha iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the thermal treatment. It was observed that the particle sizes and the thermal stability of the iron oxide phases strongly depend on the preparation method. At temperatures above 400 degrees C, the gamma-phase begins to transform to the alpha-phase.