1. Key Laboratory of Magnetic Suspension Technology and Maglev Vehicle (Ministry of Education), School of Electrical Engineering, Southwest Jiaotong University, Chengdu, China
2. Southwestern Institute of Physics, Chengdu, China
3. Key Laboratory of materials and surface technology, Ministry of Education, School of Materials Science and Engineering, Xihua University, Chengdu, China
4. School of Physics and Energy, Fujian Normal University, Fuzhou, China