Interface structure and bias dependence of Fe/MgO/Fe tunnel junctions:: Ab initio calculations

Ab initio calculations of the current voltage (IV) characteristics in planar Fe/MgO/Fe tunnel junctions are presented. The electronic and magnetic structure of the junctions is calculated self-consistently in the framework of density functional theory. The bias dependence of the tunneling current and of the differential conductance is calculated in the limit of coherent tunneling for parallel and antiparallel alignment of the electrode magnetizations. Completely different IV characteristics are obtained as a function of the interface atomic structure. In agreement with experiments the tunneling magnetoresistance ratio of the tunneling current for parallel and antiparallel alignment can even change the sign as a function of bias. Details of the bias dependence are discussed in relation to the electronic structure. The obtained features of the IV characteristic can be explained by the density of states at the interfaces taking into consideration the symmetry of tunneling states.