Field-driven closure of the Haldane gap in an ideal coordination polymer spin-chain

Chains comprising integer spin magnetic moments exhibit the celebrated non-magnetic Haldane phase, which is very different relative to the half-integer spin equivalent. We have recently discovered and characterised a molecule-based magnet system which is an ideal example of a Haldane chain, NiI2(3,5-lut)4. Crucially, deviations from the idealised spin-one chain are exceedingly small in this compound. Zero-field Inelastic neutron scattering at ISIS was successfully used to study the magnetic excitations in this system at zero-field, including the presence of the famous Haldane gap, and these data form part of an upcoming publication. We now propose to extend this study to non-zero magnetic fields, in order to investigate the field-driven evolution of the excitation spectrum up to and beyond the field-induced quantum phase transition where the Haldane gap is closed.