Fabrication and properties of heteroepitaxial magnetite (Fe3O4) tunnel junctions

Micron-size magnetic tunnel junctions consisting of ferromagnetic ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}$ electrodes, with MgO as a barrier layer, have been fabricated on (100) MgO substrates. Reflection high-energy electron diffraction and transmission electron microscopy studies reveal that the ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}{\mathrm{/MgO/Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}$ trilayers grown by pulsed laser deposition are heteroepitaxial with abrupt interfaces. To achieve different coercivities for the top and bottom ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}$ layers, the trilayers are grown on MgO substrates with a ${\mathrm{CoCr}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ buffer layer. The junctions exhibit nonlinear current–voltage characteristics and changes in junction resistance with applied field corresponding to the coercivities of the two magnetic layers. However, the observed magnetoresistance (∼0.5% at 300 K, ∼1.5% at 150 K) is much lower than would be expected for a highly spin-polarized system. Possible reasons for the reduced magnetoresistance are discussed.