1. Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
2. Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
3. Center for Spintronics Research Network, Osaka University, Toyonaka 560-8531, Japan
4. Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai 980-0845, Japan
5. WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
6. Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan
7. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
8. Department of Physics Engineering, Mie University, Tsu, Mie 514-8507, Japan