1. Department of Electronic Engineering, University of York, York, UK
2. Institute for Materials Research, Tohoku University, Sendai, Japan
3. Center for Spintronics Research Network, Tohoku University, Sendai, Japan
4. Center for Science and Innovation in Spintronics, Core Research Cluster, Tohoku University, Sendai, Japan
5. Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, Tsukuba, Japan
6. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Japan