Tuning the microstructural and magnetic properties of CoFe 2 O 4 /SiO 2 nanocomposites by Cu 2+ 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, Co 1- x Cu x Fe 2 O 4 (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO 2 matrix were prepared by a sol-gel method. The effect of a small Cu 2+ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mössbauer spectroscopy, and VSM. It was found that single cubic Co 1- x Cu x Fe 2 O 4 ferrite was formed in amorphous SiO 2 matrix. The average crystallite size of Co 1- x Cu x Fe 2 O 4 increased from 18 to 36 nm as Cu 2+ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu 2+ 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 Cu 2+ 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 Cu 2+ doping content in Co 1- x Cu x Fe 2 O 4 NPs plays an important role in its magnetic properties.