1. Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai 980-8572, Japan
2. Center for Science and Innovation in Spintronics, Tohoku University, Sendai 980-8577, Japan
3. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
4. Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan
5. Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan