Coherent tunnelling conductance in magnetic tunnel junctions of half-metallic full Heusler alloys with MgO barriers

We have carried out electronic structure and transport calculations for magnetic tunnel junctions (MTJ) composed of MgO and a half-metallic full Heusler alloy Co2MnSi on the basis of the density functional theory and the Landauer formula. We find that the density of states of Co atoms at the Co2MnSi/MgO(001) interface shifts toward the higher energy side due to the reduced symmetry, leading to a reduction of the spin polarization at the interface. Furthermore, we show that the majority-spin transmittance as a function of the in-plane wavevector k parallel to has a broad peak centred at k(parallel to) = (0, 0) due to the tunnelling from the Delta(1) channel of Co2MnSi, while the transmittance from the Delta(5) channel is three orders of magnitude smaller than that of the Delta(1) channel. These results indicate that coherent tunnelling through the Delta(1) band is dominant also in an MTJ with Co2MnSi and an MgO barrier, like in Fe/MgO/Fe(001) MTJ and related systems.