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

The raw nano α-Fe₂O₃ powders consisting of nanorods with 50–100 nm in length and 8–14 nm in width exhibit superparamagnetism. The vacuum annealing of the raw nano α-Fe₂O₃ at 400 °C for 3 h leads to ferromagnetic-like behaviors at room temperature (RT), due to the appearance of ferrimagnetic Fe₃O₄. The α-Fe₂O₃/Fe₃O₄ composite structure has an antiferromagnetic α-Fe₂O₃ layer and a ferrimagnetic Fe₃O₄ layer contains a certain amount of Fe²⁺ and oxygen vacancies. In addition, nano α-Fe₂O₃ annealed in H₂ at 300 °C for 3 h completely become Fe₃O₄. Some magnetic properties of the α-Fe₂O₃/Fe₃O₄, 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-Fe₂O₃ and the Fe₃O₄, these magnetic properties cannot be modulated by applied external RT electric field. The electric field control of magnetic properties for the α-Fe₂O₃/Fe₃O₄ should be due to the mechanism of phase transition induced by migration and redistribution of oxygen vacancies within the interface of α-Fe₂O₃/Fe₃O₄.