1. Institute for Applied Physics and Center for Nanotechnology, University of Muenster, 48149 Muenster, Germany
2. Kotel'nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 125009 Moscow, Russia
3. Institute of Physics and Center for Nanotechnology, University of Muenster, 48149 Muenster, Germany
4. Institute of Metal Physics, Ural Division of RAS, Yekaterinburg 620041, Russia