1. School of Materials Science and Engineering , Xiamen University of Technology, Xiamen , P.R. China
2. Fujian Provincial Key Laboratory of Functional Materials and Applications , Xiamen , P.R. China
3. School of Materials Science and Engineering , University of Science and Technology Beijing, Beijing , P.R. China
4. Department of Physics , University of Science and Technology Bannu, Khyber Pakhtunkhwa , Pakistan