Effect of Co ions on the microstructure and magnetic properties of nanocrystalline CoxFe3−xO4 films

Co_xFe_3−xO₄ nanocrystalline films (x=0.2-0.8$x=0.2-0.8$) on SiO₂ substrates were prepared by a sol–gel method. The microstructural and magnetic properties of samples were measured by an X-ray diffractometer (XRD) and a vibrating sample magnetometer (VSM), respectively. Atomic force microscopy (AFM) was used to investigate the surface image of the sample. The measurement results of XRD at room temperature show that the pure spinel structure of the film could be obtained at x=0.8$x=0.8$. The magnetic measurements reveal the magnetic properties of the samples depend strongly on Co²⁺ ions content, and the optimal parameters of the saturation magnetization and coercivity in Co_xFe_3−xO₄films are obtained at x=0.8$x=0.8$. Here the coercivity reaches 1.954 kOe. The average grain sizes of the film are less than 30 nm obtained from the microscopy images. The situ measurement at high temperatures of range from 293 to 773 K shows that the microstructures of Co_0.8Fe_2.2O₄ film have good thermal stabilization.