Half-metallic surfaces in thin-film Ti₂MnAl_0.5Sn_0.5

Materials exhibiting a high degree of spin polarization are in demand in spintronics. Room-temperature half-metals are considered ideal candidates, as they behave as an insulator for one spin channel and as a conductor for the other spin channel. In addition, for nano-size devices, one has to take into account possible modification of electronic structure in thin-film geometry, due to the potential presence of surface/interface states. Typically, these states have a detrimental impact on half-metallicity. Here, we employ density functional calculations to explore an inverse Heusler compound, Ti₂MnAl_0.5Sn_0.5, which exhibits half-metallic electronic structure in bulk geometry. We show that in thin-film geometry, the type of termination surface has a decisive effect on half-metallicity of this material. In particular, we analyze six possible termination configurations, and show that for four of them, energy states emerge in the minority-spin band gap, significantly reducing the spin polarization. At the same time, two termination surfaces preserve half-metallic properties of this material. Thus, our results show that a judicious choice of the termination surface may be a crucial factor in nano-device applications, where highly spin-polarized current is needed.