Exchange bias and phase transformation in α-Fe2O3/Fe3O4 nanocomposites

The phase transformation and magnetic properties of antiferromagnetic (AFM) α-Fe2O3/ferromagnetic (FI) Fe3O4 nanocomposites have been investigated. A large negative exchange bias field is observed for α-Fe2O3 powders milled for 6 h, due to the existence of the exchange interaction between AFM α-Fe2O3 and FI Fe3O4. In addition, an obvious exchange bias is found in powders with either AFM α-Fe2O3 or FI Fe3O4 single phase coated by an amorphous layer, indicating that the interfacial status and domain structure may play very important roles on the exchange interaction between the grains.