Half-metallic behavior of Co₂MnSi/Co₂MnAl/MgO interface and its coherent tunneling conductance

We study electronic and transport properties of Co₂MnSi/Co ₂MnAl/MgO(001) junctions on the basis of the first-principles density functional calculations. We found that an insertion of thin Co₂MnAl layers into a Co₂MnSi/MgO junction can eliminate interface states in the minority-spin gap and provide a 100% spin-polarization at the interface. A transfer of electrons from the minority- to majority-spin states of interfacial Mn atoms plays an important role to recover the half-metallic gap in the MnAl-terminated interface. Furthermore, the magnetic tunnel junction with Co₂MnSi/(Co₂MnAl)_n/MgO(001) (n=1∼3) retains coherent tunneling of the Δ₁-band electrons in parallel magnetization, which is in contrast to that with Co₂MnSi/(Co ₂CrAl)_n/MgO(001) where the tunneling of the Δ₁-band electrons is reduced significantly at the Co ₂CrAl layer.