Magnetic and Mössbauer spectroscopy studies of CoFe2O4/CoFe2 nanocomposites

CoFe 2 O 4 /CoFe 2 nanocomposites with exchange coupling behavior have been obtained from a two-step process. First, CoFe 2 O 4 nanoparticles with size of 11 nm were synthesized using a co-precipitation method. And second, the as-synthesized CoFe 2 O 4 nanoparticles were reduced under mixed gas (Ar 95% + H 2 5%) for 1 h at different temperatures. The structure, phase, particle size, morphology, and magnetic properties with the reduction temperature were studied. X-ray diffraction and Mössbauer spectroscopy results show the whole process from pure CoFe 2 O 4 hard magnetic phase to pure CoFe 2 soft magnetic phase when the reduction temperature increases from 400 to 700 °C, and CoFe 2 O 4 /CoFe 2 hard/soft nanocomposites are obtained at 500 and 600 °C. Magnetic measurement result show there is a stronger exchange coupling interaction between CoFe 2 O 4 and CoFe 2 for the sample reduced at 500 °C, but not in the sample reduced at 600 °C. A giant 76% enhancement of the maximum magnetic energy product (BH) max compared with pure CoFe 2 O 4 will be of technological significance in the future.