1. Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany
2. Peter Gruenberg Institute (PGI 7 & 10), Forschungszentrum Juelich GmbH, and JARA-FIT, 52428 Juelich, Germany
3. Institute of Materials in Electrical Engineering and Information Technology II, RWTH Aachen University, 52056 Aachen, Germany