1. York-Nanjing Joint
Center for Spintronics and Nanoengineering, School of Electronics
Science and Engineering, Nanjing University, Nanjing 210093, China
2. Spintronics and Nanodevice Laboratory,
Department of Electronics, University of York, York YO10 5DD, U.K.
3. Department of Physics, The University of Hong Kong, Pokfulam, Hong Kong
4. Department
of Physics, Southeast University, Nanjing 211189, China
5. Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE, U.K.