Jahn-Teller stabilization of a \"Polar\" metal oxide surface: Fe3O4(001)

Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wavelike structure along the direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed via x-ray diffraction analysis. The stabilization of the Fe3O4(001) surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a half metal to metal transition