Structural and magnetic properties of CoFe2O4/CoFe2/SiO2 nanocomposites with exchange coupling behavior

The CoFe2O4/CoFe2/SiO2 nanocomposites with exchange coupling behavior were prepared by reducing CoFe2O4/SiO2 nanocomposites in hydrogen at different temperatures. The effects of the reduction temperature on their structural and magnetic properties were studied at room temperature. The results of X-ray diffraction and Mössbauer spectroscopy indicated that the magnetic nanoparticles in the nanocomposites transformed from the hard magnetic CoFe2O4 to the soft magnetic CoFe2 with increasing reduction temperature, and the two phases coexisted in the nanocomposite reduced at 600 °C. The magnetic measurement suggested that the coercivity of the nanocomposites increased with increasing reduction temperature, reaching a maximum value at 500 °C, and then decreased significantly with further increasing reduction temperature, while the saturation magnetization of the nanocomposites increased obviously except for the nanocomposite reduced at 700 °C. The hysteresis loop of the nanocomposite reduced at 600 °C behaved like a single magnetic phase with higher saturation magnetization and coercivity. This indicated that coherent magnetization rotation and strong exchange coupling between hard magnetic CoFe2O4 and soft magnetic CoFe2 nanoparticles.