1. Institute of Microelectronics, Peking University, Beijing 100871, China
2. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
3. Fert Beijing Institute, MIIT Key Laboratory of Spintronics, School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, China
4. School of Information Science and Engineering, Shandong University, Qingdao 266237, China
5. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States