Effect of Co 2 + content on the magnetic properties of Co x Fe 3 − x O 4 /SiO 2 nanocomposites

Non-stoichiometric Co x Fe 3 − x O 4 /SiO 2 (x = 0.8, 0.9, 1.0, 1.1) nanocomposites have been prepared by sol-gel method. The structure, morphology and magnetic properties of the obtained samples were characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. As the Co 2 + content increases, the average particle size of the spherical Co x Fe 3 − x O 4 in the samples decreases and the lattice constants increases. The hyperfine fields for both A- and B-site decrease, while the fraction of Co 2 + occupying the A-site increases. Magnetization measurements show the saturation magnetization and coercivity of Co x Fe 3 − x O 4 /SiO 2 decrease with increasing Co 2 + content. The decrease in magnetization results from the weakened A-B interactions between Fe 3 + , and the change in coercivity can be related to the variation of Co 2 + at B-site and the decreasing particle size.