1. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China
2. Department of Electronic Engineering, York-Nanjing International Center in Spintronics, The University of York, York YO10 5DD, United Kingdom
3. Nanjing University of Posts and Telecommunications (NJUPT), Nanjing 210023, People's Republic of China
4. Department of Electronic Engineering, Royal Holloway University of London Egham, Surrey TW20 0EX, United Kingdom