1. School of Materials Science and Engineering; University of Science and Technology of Beijing; Beijing 100083 P. R. China
2. State Key Laboratory for Magnetism; Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; Beijing 100190 P. R. China
3. School of Materials Science and Engineering; South China University of Technology; Guangzhou 510640 P. R. China
4. Key Laboratory of Magnetic Materials and Devices; Ningbo Institute of Material Technology and Engineering; Chinese Academy of Sciences; Ningbo 315201 P. R. China
5. University of Chinese Academy of Sciences; Beijing 100049 P. R. China