1. Peter Grünberg Institute (PGI-6) Jülich Research Center 52428 Jülich Germany
2. TASC Laboratory CNR-IOM 34149 Trieste Italy
3. Department of Physics University of Trieste 34127 Trieste Italy
4. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE) University of Duisburg-Essen 47048 Duisburg Germany
5. Department of Physics and Astronomy UC Davis Davis CA 95616 USA