1. Institute for Materials Research, Tohoku University 1 , Sendai 980-8577, Japan
2. Department of Materials Science, Graduate School of Engineering, Tohoku University 2 , Sendai 980-8579, Japan
3. Center for Spintronics Research Network, Tohoku University 3 , Sendai 980-8577, Japan
4. Research Institute of Electrical Communication, Tohoku University 4 , Sendai 980-8577, Japan
5. Department of Electronic Engineering, Graduate School of Engineering, Tohoku University 5 , Sendai 980-8579, Japan
6. Center for Science and Innovation in Spintronics, Core Research Cluster, Tohoku University 6 , Sendai 980-8577, Japan