Fabrication and magnetoresistance properties of spin-dependent tunnel junctions using an epitaxial Fe3O4 film

Magnetoresistance of spin-dependent tunnel junctions has been studied using a high-quality epitaxial Fe3O4 film. The bottom magnetic electrodes of epitaxial Fe3O4 were grown onto the TiN-buffered (110) surface of MgO single-crystal substrates, and trilayer junctions of Fe3O4/AlOx/CoFe mesa were fabricated by sequential sputtering and Ar ion etching. The junctions showed the magnetoresistance (MR) ratio of more than 10% at room temperature with butterfly-like hysteresis which arose from the different coercive fields between Fe3O4 and CoFe when the field was applied along the easy axis of the epitaxial Fe3O4 layer. The MR ratio remained almost constant against the temperature down to nearly 100 K. Below 100 K, the decrease of MR and the increase of junction resistance were observed, which may be related to the Verwey transition that inevitably occurs in the characteristic of high-quality Fe3O4 samples.