Effect of annealing temperature on structure and magnetic properties of sol–gel synthesized Co0.8Fe2.2O4/SiO2 nanocomposites

Using SiO2 as amorphous matrix, Co0.8Fe2.2O4/SiO2 nanocomposites were synthesized by sol–gel method. The effect of annealing temperature on structure, cation distribution, and magnetic properties was investigated by X-ray diffraction (XRD), Mossbauer spectroscopy, and vibrating sample magnetometer (VSM). All Co0.8Fe2.2O4 in obtained composites exhibit cubic spinel structure after annealed at 500 °C and above. The particle size of Co0.8Fe2.2O4 increases from 5 to 25 nm as the annealing temperature increases from 500 to 1100 °C. Analysis of Mossbauer and VSM reveal that higher annealing temperature induces the migration of Fe3+ from octahedral B to tetrahedral A sites, which results in the enhancement in magnetic hyperfine field Hin. While the increasing content of Co2+ at B sites and the weakened ‘pinning’ effect of domain wall result in the increase of coercivity Hc. In addition, larger Co0.8Fe2.2O4/SiO2 particles exhibit higher saturation magnetization Ms due to the relative decrease in magnetically disordered content on the Co0.8Fe2.2O4 surface.