1. Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
2. Department of Applied Physics, Faculty of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-8656, Japan
3. Center for Spintronics Research Network, Graduate School of Engineering Science, Osaka University, Machikaneyama 1-3, Toyonaka, Osaka 560-8531, Japan