1. Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
2. WPI-Advanced Institute for Materials Research (AIMR), Tohoku University, 2-1-1, Katahira, Sendai, Miyagi 980-8577, Japan
3. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
4. Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
5. Center for Science and Innovation in Spintronics, Core Research Cluster, Tohoku University, Sendai 980-8577, Japan