NBCT is an S = 1 antiferromagnetic nickel chain near the D/J quantum critical point*

An S=1 antiferromagnetic chain, [Ni(HF2)(3-Clpy)₄]BF₄ (py = pyridine), henceforth NBCT, has been reported to be in the intermediate, in-plane anisotropy limit, which is a region of phase space that has not been tested quantitatively against theoretical predictions (large D and small D have both been investigated thoroughly). The best fit Hamiltonian parameters for NBCT from magnetization and specific heat have the easy-plane anisotropy D = 4.3 K, the intrachain antiferromagnetic interaction J = 4.86 K, and the interchain interaction J’ to be negligible, such that D/J = 0.88 in the vicinity of the D/J≈1 quantum critical point. Here, we present inelastic powder neutron scattering data that can be compared with density matrix renormalization group theory.