1. Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
2. Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
3. Department of Physics, Ajou University, Suwon 16499, Republic of Korea
4. Quantum Spin Team, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea
5. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States