The exchange coupling interaction in CoFe2O4/Fe3O4 hard and soft magnetic nanocomposites

Nanocomposites containing hard and soft magnetic phases have attracted a lot of attentions for their excellent magnetic properties. In this work, the hard and soft magnetic nanocomposites CoFe2O4/Fe3O4 were prepared using a co-precipitation method, and the structural, morphological and magnetic characterizations were researched. The X-ray diffraction revealed the formation of spinel ferrites, and the average crystallite sizes were about 15-18 nm. When the concentration of soft ferrite Fe3O4 increased, there were some bigger spherical and cubic-like particles in the images of the field emission scanning electron microscopy and transmission electron microscopy. Energy dispersive X-ray analysis, Mossbauer spectroscopy and magnetic measurement demonstrated the co-existence of CoFe2O4 and Fe3O4 phases in nanocomposites, and the improvement of the magnetic properties indicated there was a good exchange-coupling interaction between the hard and soft magnetic phases. For the sample with a mass ratio of CoFe2O4 to Fe3O4 being 1:1, the value of (BH)(max) at 300 K and 77 K are about 35% and 842% higher than those of the pure CoFe2O4, respectively.