1. State Key Laboratory
of Optoelectronic Materials and Technologies, School of Physics and
Engineering, Sun Yat-Sen University, Guangzhou 510275, China
2. Center for Magnetic
Recording Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0401, United States
3. Department
of Physics and Hefei National Laboratory for Physical Sciences at
Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
4. The Institute
of Applied Physics and Materials Engineering, University of Macau, Avenida da
Universidade, Taipa, Macau 999078, China