1. London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WCH1 0AH, United Kingdom
2. Department of Applied Physics, Tohoku University, Aoba 6-6-05, Sendai 980-8579, Japan
3. WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Sendai 980-8577, Japan
4. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
5. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
6. Center for Science and Innovation in Spintronics, Tohoku University, Sendai 980-8577, Japan
7. Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom