First principles electronic structure and transport calculations are used to demonstrate the impact of the electric polarization on electron and spin transport in multiferroic tunnel junctions (MFTJs). We find that the polarization of reduces the tunneling conductance, as compared to a nonpolarized barrier, due to the change in the electronic structure driven by ferroelectric displacements, similar to that found previously for . For the MFTJ, however, this effect has different magnitudes for majority- and minority-spin channels and for parallel and antiparallel orientations of the magnetization of the electrodes. As a result, we find a substantial drop in the spin polarization of the tunneling current in the parallel configuration and an inversion of the magnetoresistance as polarization of the barrier is turned on.
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Energy cutoff of in the plane wave expansion and a Monkhorst-Pack -point grid were used. Structural relaxations are performed until the Hellman-Feynman forces on atoms become less than .
We use atomic spheres of radii , , , and . For space filling we introduce an empty sphere of radius at each interface. The quality of this choice of the spheres is tested against VASP calculations. A grid of points was used. Combined correction was used and , , and orbitals were downfolded.
