1. Center for Spintronics Research Network, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
2. Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan
3. The Institute of Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
4. Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan
5. Center for Spintronics Research Network, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan