1. Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, D-52425 Jülich, Germany
2. Jülich-Aachen Research Alliance (JARA-FIT), D-52425 Jülich, Germany
3. Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden
4. Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47057 D-Duisburg, Germany