$\left[\mathrm{Ni}\left({\mathrm{HF}}_2\right){\left(3\text{−}\mathrm{Clpyradine}\right)}_4\right]\mathrm{B}{\mathrm{F}}_4$ (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.

• Received 14 February 2022
• Accepted 31 March 2022

DOI:https://doi.org/10.1103/PhysRevB.105.134420