1. Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan
2. Research Institute for Electronic Science (RIES), Hokkaido University, Sapporo 001-0020, Japan
3. MANA, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
4. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
5. National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
6. Center for Spintronics Research Network (CSRN), Keio University, Yokohama 223-8522, Japan