1. Neutron Group, National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan
2. Laboratory for Quantum Magnetism, Institute of Physics, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne, Switzerland
3. Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
4. University Grenoble Alpes, CEA, INAC-MEM, 38000 Grenoble, France