1. Hefei Innovation Research Institute School of Integrated Circuit Science and Engineering Beihang University Hefei 230013 P. R. China
2. College of Electronic and Information Engineering Shenzhen University Shenzhen 518060 P. R. China
3. Fert Beijing Institute MIIT Key Laboratory of Spintronics School of Integrated Circuit Science and Engineering Beihang University Beijing 100191 P. R. China