Ab initio study of electronic and magnetic properties of Mn₂RuZ/MgO (001) heterojunctions (Z = Al, Ge)

We studied the applicability of Heusler alloys Mn2RuZ (Z = Al, Ga, Ge, Si) to the electrode materials of MgO-based magnetic tunnel junctions. All these alloys possess Hg2CuTi-type inverse Heusler alloy structure and ferrimagnetic ground state. Our study reveals the half-metallic electronic structure with highly spin-polarized Δ1 band, which is robust against atomic disorder. Next we studied the electronic structure of Mn2RuAl/MgO and Mn2RuGe/MgO heterojunctions. We found that the MnAl- or MnGe-terminated interface is energetically more favorable compared to the MnRu-terminated interface. Interfacial states appear at the Fermi level in the minority-spin gap for the Mn2RuGe/MgO junction. We discuss the origin of these interfacial states in terms of local environment around each constituent atom. On the other hand, in the Mn2RuAl/MgO junction, high spin polarization of bulk Mn2RuAl is preserved independent of its termination.