$[\mathrm{Ni}({\mathrm{HF}}_{2}){(3\text{\ensuremath{-}}\mathrm{Clpyradine})}_{4}]\mathrm{B}{\mathrm{F}}_{4}$ (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.
$[\mathrm{Ni}({\mathrm{HF}}_{2})(3\ensuremath{-}\text{Clpyridine}){}_{4}]{\mathrm{BF}}_{4}$ (NBCT) is a one-dimensional,
S=1 spin chain material that shows no magnetic neutron Bragg peaks down to temperatures of 0.1 K. Previous work identified NBCT as being in the Haldane phase and near a quantum phase transition as a function of
D/J to the large-
D quantum paramagnet phase (QPM), where
D is the axial single-ion anisotropy and
J is the intrachain superexchange. Herein, inelastic neutron scattering results are presented on partially deuterated,
11B-enriched NBCT polycrystalline samples in zero magnetic field and down to temperatures of 0.3 K. Comparison to density matrix renormalization group calculations yields
D/J=1.51 and a significant rhombic single-ion anisotropy
E ($E/D\ensuremath{\approx}0.03, E/J\ensuremath{\approx}0.05$). These
D,J, and
E values place NBCT in the large-
D QPM phase but precipitously near a quantum phase transition to a long-range ordered phase.