1. Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland
2. COMP Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
3. Peter-Grünberg-Institut (PGI-1) and JARA/HPC, Forschungszentrum Jülich, D-52425 Jülich, Germany