1. Institute of Physics; University of Münster, Heisenbergstr. 11; 48149 Münster Germany
2. Institute of Nanotechnology; Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1; 6344 Eggenstein-Leopoldshafen Germany
3. Fraunhofer Institute of Applied Solid State Physics (IAF); Tullastr. 72; 79108 Freiburg Germany
4. EPCOS AG; Anzinger Strasse 13; 81671 Munich Germany