Tuning the structure of ultrathin BaTiO3 films on Me(001) (Me=Fe, Pd, Pt) surfaces.

Using surface x-ray diffraction in combination with ab initio calculations, we demonstrate that the atomic structure of ultrathin BaTiO3 (BTO) films grown on Me(001) surfaces (Me=Fe, Pd, Pt) depends on subtle modifications of the interface chemical composition. A complete reversal of the surface termination from a BaO- [BTO on Fe(001)] to a TiO2-terminated film [BTO on Pt(001)] is observed which goes in parallel with the adsorption of submonolayer amounts of oxygen at metal hollow sites of the interface. Our results may suggest a new route to an overall control of both the surface and the interface geometry in BaTiO3/metal contacts.

BaTiO3(001)-(2×1): surface structure and spin density.

Using surface x-ray diffraction and ab initio calculations we present a model of the BaTiO3(001)-(2×1) surface structure, which has not been considered so far. While the crystal is terminated by two TiO2 layers similarly to SrTiO3(001)-(2×1), 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 2μ(B) in magnitude located at surface Ti and O atoms.

Structural secrets of multiferroic interfaces.

We present an experimental and theoretical study of the geometric structure of ultrathin BaTiO(3) films grown on Fe(001). Surface x-ray diffraction reveals that the films are terminated by a BaO layer, while the TiO(2) layer is next to the top Fe layer. Cations in termination layers have incomplete oxygen shells inducing strong vertical relaxations.