Study on structure and magnetic properties of rare earth doped cobalt ferrite: The influence mechanism of different substitution positions

Rare earth (RE) doped cobalt ferrite (CFO) nanoparticles were synthesized by sol-gel auto combustion method, and the effect mechanism of RE3+ replacing Co2+ or Fe3+ on CFO was studied for the first time. The different roles of RE added to CFO in changing cation distribution and further affecting structure and magnetism properties due to different substitution positions were focused. The crystal structure formation and crystallite size were investigated by XRD and the results showed that the replacement of Co2+ ions by RE3+ ions was more likely to lead to larger lattice distortion and smaller grains compared with the replacement of Fe3+ ions by RE3+ ions. The SEM and TEM results showed that RE3+ doping not only reduced the grain size, but also made the grain distribution more uniform. The FTIR analysis confirmed that the synthesized material belonged to the spinel structure, and the results also showed that the space shrinkage of tetrahedron (A-sites) was more likely to be caused by the substitution of RE3+ for Co2+ ions. Room temperature magnetization measurements showed that the saturation magnetization of CFO decreased with the substitution of RE3+ ions, and the change of coercivity was related to the substitution position and type of RE3+ ions. The coercivity increased significantly with the substitution of Co2+ ions by RE3+, reaching a maximum of 2423 Oe (Co0.8Gd0.2Fe2O4), and decreased with the substitution of Fe3+ ions by RE3+. Due to the difference of grain size and RE3+ doping, the magnetic domain presents single or multi domain structure. It can be concluded that the substitution of RE3+ ions for different ions will cause cation rearrangement, and then the cation rearrangement and grain size together lead to a large change in the coercivity of CFO, which puts forward a new direction for the subsequent improvement of the coercivity of materials.