1. Department of Physics, University of York, York YO10 5DD, United Kingdom
2. York-Nanjing International Joint Center in Spintronics, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
3. Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
4. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
5. Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD, United Kingdom
6. Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, Sheffield S1 1WB, United Kingdom
7. Département de Physique, L'Université de Liège, B-4000 Liège, Belgium
8. Department of Physics, Southeast University, Nanjing 210096, China