Preparation and characterization of core–shell structured Co/SiO2 nanosphere

Abstract The Co/SiO 2 nanospheres have been prepared by the improved sol–gel method combined with hydrogen reduction. The size, the phase and the shape of the particles varied with the molar ratio of SiO 2 , reduction temperature and drying temperature. The initial temperature of the phase transformation from hcp-Co to fcc-Co in core–shell structured Co/SiO 2 nanospheres is lower than that in the bulk case due to the lower surface energy of nanoscale particles. Result of the thermogravimetric analysis (TGA) indicates that the thermal stability of Co/SiO 2 nanoparticles is much better than that of pure Co particles. The value of saturation magnetization decreases with the increase of SiO 2 content due to the presence of the nonmagnetic silica coating.