Tailoring magnetic properties of cobalt ferrite nanoparticles by different divalent cation substitution

Different divalent cation substituted Co-ferrite (M X Co 1−X Fe 2 O 4 , where M = Mg 2+ , Ni 2+ , Cu 2+ , Zn 2+ , with x = 0.20 and 0.75) nanoparticles were synthesized by sol–gel method and were annealed at 900 °C in air. After annealing, grain growth was observed for all the samples. With the substitution of Mg 2+ , Ni 2+ and Cu 2+ with x = 0.20, the magnetization of the as-prepared and the annealed samples was decreased from that of the Co-ferrite whereas Zn 2+ substitution enhanced the magnetization. The highest magnetization values of 79.9 and 92.9 emu/g at 300 and 60 K respectively were observed for the Zn 2+ substituted annealed sample with x = 0.20. For higher concentration of x = 0.75, the magnetization value was further decreased in all the samples and the lowest magnetization value of 5.1 emu/g was observed in the Zn 2+ substituted annealed sample with x = 0.75 at 300 K. The coercivity was reduced in the samples except for the Cu 2+ substituted sample. In the Cu 2+ substituted sample with x = 0.75, the highest coercivity of 1.43 kOe at 300 K was observed after annealing. The changed cation distribution in the spinel structure, ionic magnetic moment and anisotropy compared to the Co 2+ in these nanomaterials can explain the observed magnetic properties.