High-pressure inelastic neutron scattering study of the anisotropic S=1 spin chain [Ni(HF2)(3-Clpyradine)(4)]BF4

[Ni(HF2)(3-Clpyradine)(4)]BF4 (NBCT) is a one-dimensional, S = 1 spin-chain material that shows no long-range magnetic order down to thermometer temperatures of 0.1 K. Previous ambient pressure inelastic neutron scattering experiments identified NBCT to be in the large-D quantum paramagnetic phase of the D/J phase diagram, where D is the axial single-ion anisotropy and J is the intrachain superexchange. Here, we extend the previous experiments to a hydrostatic pressure of 0.9 GPa. By comparing to density matrix renormalization group calculations, we find D/J increases from 1.5 to 3.2 as pressure increases from 0 GPa to 0.9 GPa, which pushes the system further into the large-D phase.