Tuning the microstructural and magnetic properties of CoFe2O4/SiO2 nanocomposites by Cu2+ doping

Co-Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co1-xCuxFe2O4 (0 <= x <= 0.3) nanoparticles (NPs) embedded in a SiO2 matrix were prepared by a sol-gel method. The effect of a small Cu2+ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mossbauer spectroscopy, and VSM. It was found that single cubic Co1-xCuxFe2O4 ferrite was formed in amorphous SiO2 matrix. The average crystallite size of Co1-xCuxFe2O4 increased from 18 to 36 nm as Cu2+ doping content x increased from 0 to 0.3. Mossbauer spectroscopy indicated that the occupancy of Cu2+ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu(2+)doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu2+ content increasing, the saturation magnetization (M-s) first increased, then tended to decrease, while the coercivity (H-c) decreased continuously, which was associated with the cation migration. The results suggest that the Cu2+ doping content in Co1-xCuxFe2O4 NPs plays an important role in its magnetic properties.