[Nordita Program] Structure modifications in ultra thin films of transition metal oxides

by Holger Meyerheim (MPI für Mikrostrukturphysik, Halle)

Wednesday 17 Feb 2010, 11:00 → 12:00 Europe/Stockholm

Nordita Seminar Room

The talk reviews recent studies on the geometric structure of oxide films in the ultra thin film limit and their implications on their magnetic (multiferroic) properties. In a first example the structural phase transition in pure and Cobalt-doped ZnO-film is discussed. Depending on film thickness a transition from the bulk Wurtzite (WZ)- type structure to the hexagonal-Boron-nitride (h-BN) phase is observed. Cobalt doping leads to a phase segregation in which WZ-type CoO-nanoclusters are coherently embedded into the h-BN host ZnO matrix. The structure model involving locally confined antiferromagnetic CoO-clusters supports recent experimental results on the magnetic properties of diluted magnetic semiconductors. The effect of confinement is also decisive for the multiferroic (ferromagnetic/ferroelectric) properties of the BaTiO3/Fe(001) interface, which is addressed in the second part of the talk. The structure analysis in combination with first principles calculations reveals the onset of an interface dipole at a critical film thickness of two unit cells of BaTiO3. Its influence on the magnetoelectric properties is discussed.