1. Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, South Korea
2. Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology, Seoul 02792, South Korea
3. School of Electrical Engineering, Kookmin University, Seoul 02707, South Korea
4. KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, South Korea
5. Division of Nano and Information Technology, KIST School, Korea University of Science and Technology, Seoul 02792, South Korea