1. Quantum Spin Team Korea Research Institute of Standards and Science Daejeon 34113 Republic of Korea
2. Department of Physics Pusan National University Busan 46241 Republic of Korea
3. Division of Quantum Phases and Devices Department of Physics Konkuk University Seoul 05029 Republic of Korea
4. Department of Materials Science and Engineering Ulsan National Institute of Science and Technology (UNIST) Ulsan 44919 Republic of Korea