1. Research Institute for Electronic Science, Hokkaido University, Sapporo, Hokkaido 001-0020, Japan
2. Faculty of Science and Technology, Keio University, Yokohama, Kanagawa 223-8522, Japan
3. Graduate School of Information Science and Technology, Hokkaido University, Sapporo, Hokkaido 060-0814, Japan
4. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
5. Center for Spintronics Research Network, Keio University, Yokohama, Kanagawa 223-8522, Japan