1. Electronics and Materials Science Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, Hamamatsu, Shizuoka 432-8561, Japan
2. Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
3. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan