1. Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
2. Department of Microtechnology and Nanoscience MC2, Chalmers University of Technology, 412 96 Göteborg, Sweden
3. Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
4. Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany
5. JARA-FIT, 52056 Aachen, Germany
6. Institute for Theory of Statistical Physics, RWTH Aachen, 52056 Aachen, Germany