1. Laboratory of Spintronics and Nanodevices, Department of Electronic Engineering, University of York, York YO10 5DD, U.K.
2. York-Nanjing International Center of Spintronics, School of Electronics Science and Technology, Nanjing University, Nanjing 210093, China
3. Department of Physics, University of York, York YO10 5DD, U.K.
4. School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, U.K.
5. School of Electronics and Information, Nantong University, Nantong 226019, China