1. University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
2. National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
3. Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
4. Center for Spintronics Integrated Systems, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
5. Center for Innovative Integrated Electronic Systems, Tohoku University, 468-1 Aramaki Aza Aoba, Aoba, Sendai 980-0845 Japan
6. WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan