1. Microelectronics and Materials Physics Laboratories, University of Oulu, PO Box 4500, FI-90014 Oulun Yliopisto, Finland
2. Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
3. NanoSpin, Department of Applied Physics, Aalto University School of Science, PO Box 15100, FI-00076 Aalto, Finland
4. Ioffe Physical-Technical Institute RAS, 194021 St. Petersburg, Russia