Half-metallic properties of the (001) surfaces of vanadium-substituted Rock-salt GeTe-based compounds

We study the properties of the (001) surfaces of ternary vanadium compounds based on the rocksalt semiconductor GeTe. In one of the compounds 25% of Ge atoms are replaced by V atoms, and in another, the substitution is as large as 50%. Using a first-principles method, we calculate the electronic structure of the two systems for two different surface terminations. The studied systems are found to be half-metallic ferromagnets. The half-metallic gap in every system is found to be larger than it is in the bulk. However, in Ge-terminated surfaces, the bottom of the conduction band is very near the Fermi level, and this may cause an instability of the half-metallicity in the systems. VGe-terminated surfaces are characterized by a more stable half-metallic ferromagnetic order. The larger amount of replacement of Ge atoms by V atoms also supresses the magnetic properties of the system. The largest calculated magnetic moment on the V atom at the topmost layer of the (001) surface is 2.602 A mu (B) . The presence of a magnetic center causes polarization of the metalloids: in the 50%-substituted GeTe, Te atoms are negatively polarized, and Ge atoms are slightly positively polarized. The largest magnetic moment on Te is calculated for Te atom at the topmost layer and is -0.107 A mu (B) .