Room temperature electric field control of magnetic properties for the α-Fe2O3/Fe3O4 composite structure

Abstract The raw nano α-Fe 2 O 3 powder with an average grain size of about 8 nm exhibits superparamagnetism. The α-Fe 2 O 3 /Fe 3 O 4 composite structure obtained by vacuum annealing of the raw nano α-Fe 2 O 3 at 400°C for 3 hours has room temperature (RT) ferromagnetism. The α-Fe 2 O 3 /Fe 3 O 4 has an antiferromagnetic α-Fe 2 O 3 layer and a Fe 3 O 4 layer contains a certain amount of Fe 2+ and oxygen vacancies. The ferromagnetism of the α-Fe 2 O 3 /Fe 3 O 4 after vacuum annealing should be attribute to the Fe 3 O 4 layer and oxygen vacancies. In addition, nano α-Fe 2 O 3 annealed in H 2 at 300°C for 3 hours is completely become Fe 3 O 4 . Some magnetic properties of the α-Fe 2 O 3 /Fe 3 O 4 , such as magnetization, magnetic remanence (Mr), coercivity (Hc) and exchange bias (EB), can be modulated almost reversibly and non-volatilely by applied external RT electric field without loop current. However, for both the raw nano α-Fe 2 O 3 and the Fe 3 O 4 , these magnetic properties cannot be modulated by applied external RT electric field. The electric field control of magnetic properties for the α-Fe 2 O 3 /Fe 3 O 4 should be related to the migration and redistribution of oxygen vacancies.