1. Research Institute of Electrical Communication, Tohoku University, 980-8577, Japan
2. Center for Science and Innovation in Spintronics, Tohoku University, 980-8577, Japan
3. Center for Spintronics Research Network, Tohoku University, 980-8577, Japan
4. Center for Innovative Integrated Electronic Systems, Tohoku University, 980-0845, Japan
5. WPI-Advanced Institute for Materials Research, Tohoku University, 980-8577, Japan
6. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
7. Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
8. Institute of Physics, Johannes Gutenberg Universität Mainz, Mainz, 55128, Germany