1. Institute for Materials Research Tohoku University Sendai 980‐8577 Japan
2. Center for Spintronics Research Network Tohoku University Sendai 980‐8577 Japan
3. Research Center for Magnetic and Spintronic Materials National Institute for Materials Science Tsukuba 305‐0047 Japan
4. PRESTO Japan Science and Technology Agency Saitama 332‐0012 Japan
5. Center for Science and Innovation in Spintronics Core Research Cluster Tohoku University Sendai 980‐8577 Japan