1. Institut für Physik, Universität Greifswald, Greifswald, Germany
2. Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai, Japan
3. WPI Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
4. Center for Spintronic Research Network (CSRN), Tohoku University, Sendai, Japan
5. Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai, Japan