Sol–gel preparation and characterization of CoFe2O4–SiO2 nanocomposites

Magnetic nanocomposites formed by cobalt ferrite particles dispersed in a silica matrix were prepared by a sol–gel process. The effects of the thermal treatment temperature and the salt concentration on the structural and magnetic properties of the composites were investigated. By controlling these parameters, CoFe2O4/SiO2 nanocomposites with different crystallite size and magnetic properties were obtained. By increasing the annealing temperature and salt concentration, composites with a progressive increase in the coercive field and of the density of magnetization were produced. In particular, a nanocomposite, with a Fe/Si molar concentration of 21%, obtained by drying the gel at 150 °C and further annealing at 800 °C, has a coercivity of 2000 Oe, which is more than twice higher than the coercivity of bulk cobalt ferrite.