1. School of Physics State Key Laboratory for Crystal Materials Shandong University Jinan 250100 P. R. China
2. Key Laboratory for Magnetism and Magnetic Materials Ministry of Education Lanzhou University Lanzhou 730000 P. R. China
3. Key Laboratory of Special Function Materials and Structure Design Ministry of Education Lanzhou University Lanzhou 730000 P. R. China
4. Henan Key Laboratory of Diamond Optoelectronic Materials and Devices Key Laboratory of Material Physics Ministry of Education School of Physics and Microelectronics Zhengzhou University Zhengzhou 450052 P. R. China