1. Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education Lanzhou University Lanzhou 730000 P. R. China
2. Key Laboratory of Sensor and Sensor Technology Institute of Sensor Technology Gansu Academy of Science Lanzhou 730000 P. R. China
3. Key Laboratory for Special Function Materials and Structural Design of the Ministry of Education Lanzhou University Lanzhou 730000 P. R. China