1. Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, United Kingdom
2. Department of Physics, Oxford University, Oxford, OX1 3PU, United Kingdom
3. Laboratory for Quantum Magnetism, Ecole Polytechnique Federale de Lausanne (EPFL), CH 1015, Switzerland
4. Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland