Fe3+/Fe2+ ratio controlled magnetic and electrical transport properties of polycrystalline Fe3(1-δ)O4 films

Polycrystalline Fe3(1-delta)O4 films were fabricated using a dc reactive sputtering system, and the relative Fe3+/Fe2+ ratio in the films was adjusted slightly by changing the O-2 flow rate (OFR). The lattice structure of all the films is inverse spinel, but the Fe3+/Fe2+ ratio increases with the increasing OFR. The Verwey transition of the polycrystalline Fe3(1-d) O4 films was observed at similar to 103K from magnetic and magnetoresistance (MR) measurements, but not from the rho-T curves due to the grain-boundary controlled transport mechanism of tunnelling. With the increase in Fe3+ ions in the films, the room-temperature MR increases, and the stability of the barriers between the Fe3(1-delta)O4 grains was improved, which should be of benefit for practical application in the field of spintronic devices.