1. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
2. Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
3. QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
4. Center for Emergent Matter Science (CEMS), RIKEN, Wako, Saitama 351-0198, Japan
5. Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
6. Department of Applied Physics, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan