Inverse magnetoresistance in magnetic tunnel junction with an Fe/sub 3/O/sub 4/ 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 Fe/sub 3/O/sub 4/ without other crystallographic phases such as FeO and Fe/sub 2/O/sub 3/. To grow Fe/sub 3/O/sub 4/ 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 Fe/sub 3/O/sub 4/, inverse magnetoresistance (MR) behavior was observed, which is what is expected from the band structure of Fe/sub 3/O/sub 4/. However, when free Fe exists due to incomplete oxidation, positive MR behavior is observed.