Pressure Dependence of the Magnetic Response of the S $=$ 1 Polymeric Chain [Ni(HF2)(3-Clpy)4]BF4.*

[Ni(HF2)(3-Clpy)4]BF4 (py $=$ pyridine) is an S $=$ 1 antiferromagnetic polymeric chain with a single-ion anisotropy (zero-field splitting) of D/kB $=$ 4.3 K and an intrachain exchange interaction value of J/kB $=$ 4.86 K at ambient pressure [1]. The ratio of these parameters (D/J $=$ 0.88) places this system close to a quantum critical point at D/J $\approx $ 1, which falls between the Haldane and the Large-D phases. The temperature dependence of the low-field (1 kG) magnetic susceptibility was measured as a function of pressure, up to 1.49 GPa, using a homemade piston-clamp cell [2]. The data indicate the antiferromagnetic component is suppressed with increasing pressure. [1] J.L. Manson et al., Inorg. Chem. 51 (2012) 7520. [2] M.K. Peprah, PhD thesis, University of Florida (2015).