Effects of the iron-oxide layer in Fe-FeO-MgO-Fe tunneling junctions

First-principles calculations of the electronic structure and tunneling magnetoconductance of Fe-FeO-MgO-Fe tunneling junctions are compared to those of Fe-MgO-Fe. We find that an atomic layer of iron-oxide at the interface between Fe substrate and the MgO layer greatly reduces the tunneling magnetoconductance, due to the bonding of Fe with O which reduces the conductance when the moments in the two electrodes are aligned but has little effect when the moments are antiparallel. The TMR ratio (defined as the ratio of the change in resistance to the parallel resistance) decreases monotonically and exponentially with the increasing O concentration in the FeO layer.