1. National
Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory
for NanoTechnology, Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
2. Key
Laboratory for Magnetism and Magnetic Materials of the Ministry of
Education, Lanzhou University, Lanzhou 730000, People’s Republic of China
3. Department
of Chemistry, Hong Kong Baptist University, Hong Kong 852, People’s Republic of China