1. State Key Laboratory of Metastable Materials Science and Technology; Yanshan University; 066004 P. R. China
2. Department of Physics; Southeast University; Nanjing 211189 P. R. China
3. Northwest Institute for Non-ferrous Metal Research; Xian 710016 P. R. China
4. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; China
5. Key Laboratory of Nanodevices and Applications; Suzhou Institute of Nano-tech and Nano-bionics; Chinese Academy of Sciences; China