1. Center for Spintronics Integrated Systems, Tohoku University, Sendai 980-8577, Japan
2. Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan
3. Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai 980-0845, Japan
4. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
5. WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan