1. a Department of Material Science, Sichuan University, Chengdu 610064, P. R. China
2. International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, P. R. China
3. Department of Material Science, Sichuan University, Chengdu 610064, P. R. China.
4. Department of Material Science, Sichuan University, Chengdu 610064, P. R. China
5. Department of Physics, Civil Aviation Flying Institute of China, Guanghan 618307, P. R. China