1. Fert Beijing Research Institute, MIIT Key Laboratory of Spintronics, School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, P. R. China
2. Beihang-Goertek Joint Microelectronics Institute, Qingdao Research Institute, Beihang University, Qingdao 266101, P. R. China
3. School of Microelectronics, Xi’an Jiaotong University, Xi’an 710049, P.R. China
4. School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China