BaTiO3(001)-(2 x 1): Surface Structure and Spin Density

Using surface x-ray diffraction and ab initio calculations we present a model of the BaTiO3(001)-(2 x 1) surface structure, which has not been considered so far. While the crystal is terminated by two TiO2 layers similarly to SrTiO3(001)-(2 x 1), we find that one out of two surface layer Ti- atoms resides in a tetragonal pyramidal oxygen environment. This peculiar geometry leads to a metallic and magnetic surface involving local magnetic moments up to 2 mu(B) in magnitude located at surface Ti and O atoms. Our results are important for the understanding of the intrinsic surface metallicity of insulating oxides in general.