1. Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices, Center for Neutron Science and Technology, School of Physics, Sun Yat-Sen University, Guangzhou 510275, China
2. Department of Physics, College of Physics & Optoelectronic Engineering, Jinan University, Guangzhou, Guangdong 510632, China
3. Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697-4575, United States