1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, P. R. China
2. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, PR China
3. Department of Physics, South University of Science and Technology of China, Shenzhen, 518055, PR China
4. Department of Applied Physics and Materials
Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, PR China