1. NanoSpin Department of Applied Physics Aalto University School of Science P.O. Box 15100 Aalto FI‐00076 Finland
2. Department of Applied Physics Aalto University School of Science P.O. Box 11100 Aalto FI‐00076 Finland
3. Microelectronics Research Unit Faculty of Information Technology and Electrical Engineering University of Oulu Oulu FI‐90014 Finland