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, Co_1- Cu Fe₂O₄ (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, Mössbauer spectroscopy, and VSM. It was found that single cubic Co_1- Cu Fe₂O₄ ferrite was formed in amorphous SiO₂ matrix. The average crystallite size of Co_1- Cu Fe₂O₄ increased from 18 to 36 nm as Cu²⁺ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu²⁺ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu²⁺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 Co_1- Cu Fe₂O₄ NPs plays an important role in its magnetic properties.