Surface structures of L1₀-MnGa (001) by scanning tunneling microscopy and first-principles theory

Highlights: • Discovery of surface structures of the technologically important (001) L1₀-MnGa surface. • Two reconstructions: a 1 × 1 Ga-terminated structure and a 1 × 2 Mn substituted Ga-termination. • The 1 × 2 Mn substituted atoms couple antiferromagnetically to the underlying Mn atoms. - Abstract: We report on the surface reconstructions of L1₀-ordered MnGa (001) thin films grown by molecular beam epitaxy on a 50 nm Mn₃N₂ (001) layer freshly grown on a magnesium oxide (001) substrate. Scanning tunneling microscopy, Auger electron spectroscopy, and reflection high energy electron diffraction are combined with first-principles density functional theory calculations to determine the reconstructions of the L1₀-ordered MnGa (001) surface. We find two lowest energy reconstructions of the MnGa (001) face: a 1 × 1 Ga-terminated structure and a 1 × 2 structure with a Mn replacing a Ga in the 1 × 1 Ga-terminated surface. The 1 × 2 reconstruction forms a row structure along [100]. The manganese:gallium stoichiometry within the surface based on theoretical modeling is in good agreement with experiment. Magnetic moment calculations for the two lowest energy structures reveal important surface and bulk effects leading to oscillatory total magnetization for ultra-thin MnGa (001) films.