1. Department of Energy and Materials Engineering; Dongguk University; 26 Pil-dong, 3-ga, Jung-gu Seoul 100-715 Republic of Korea
2. School of Electronic and Optical Engineering; Nanjing University of Posts and Telecommunications; Nanjing Jiangsu 210023 China
3. Key Laboratory of Polar Materials and Devices (Ministry of Education); Technical Center for Multifunctional Magneto-Optical Spectroscopy (Shanghai); East China Normal University; Shanghai 200241 China
4. Department of Physics; National Chung Hsing University; Taichung 40227 Taiwan