1. Department of Physics School of Physical Science and Engineering Beijing Jiaotong University Beijing 100044 P. R. China
2. School of Chemical Engineering and Technology Tianjin University Molecular Plus and Collaborative Innovation Center of Chemical Science and Engineering Tianjin 300072 P. R. China
3. College of Physical Science and Technology Yangzhou University Yangzhou 225002 P. R. China
4. Key Laboratory of Photochemistry Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
5. Research Center for Magnetic and Spintronic Materials National Institute for Materials Science Tsukuba 305-0047 Japan