1. IBM Almaden Research Center; San Jose CA 95120 USA
2. Max Planck Institute for Microstructure Physics; 06120 Halle Germany
3. Graduate School of Excellence Materials Science in Mainz; Johannes Gutenberg University; Staudingerweg 9 55128 Mainz Germany
4. Fachbereich Physik; University of Kaiserslautern; Erwin-Schrödinger-Strasse 56 67663 Kaiserslautern Germany