1. Institute of Materials in Electrical Engineering and Information Technology II; RWTH Aachen University; 52056 Aachen Germany
2. Peter Grünberg Institute; Research Center Juelich GmbH and JARA-FIT; 52425 Juelich Germany
3. Eduard-Zintl-Institut; 64287 TU Darmstadt Germany
4. Institute of Physical Chemistry; RWTH Aachen University; 52056 Aachen Germany