1. RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
2. Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232 Villigen, Switzerland.
3. Department of Physics, Hokkaido University, Sapporo 060-0810, Japan.
4. Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan.
5. Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France.
6. Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
7. PRESTO, Japan Science and Technology Agency (JST), Tokyo 102-0075, Japan.