Inverse magnetoresistance in magnetic tunnel junction with an Fe3O4 electrode

Magnetic tunnel junctions (MTJ) with a plasma-oxidized Fe electrode have been fabricated on oxidized silicon wafers with standard photolithography. High-resolution transmission electron microscopy (HRTEM) and diffraction patterns show that a thin Fe layer can be oxidized by a controlled oxygen plasma into pure Fe₃O₄ without other crystallographic phases such as FeO and Fe₂O₃. To grow Fe₃O₄ directly in contact with an AlOx barrier, we began with Fe layers that varied from 1.8 to 5 nm. It was found that complete oxidation only occurred for the 1.8-nm thickness. Magnetic and electrical transport properties on the MTJs were measured at room temperature and low temperature (110 K). When the layer adjacent to the AlOx barrier was Fe₃O₄, inverse magnetoresistance (MR) behavior was observed, which is what is expected from the band structure of Fe₃O₄. However, when free Fe exists due to incomplete oxidation, positive MR behavior is observed.