Crystal Structure and Low-Dimensional Magnetism in CsNiV₂O₆Cl

Single crystals of CsNiV₂O₆Cl were grown hydrothermally. Its crystal structure (space group I2̅/a) is based on vertex-sharing twisted chains of Ni²⁺O₄Cl₂ octahedra and edge-sharing chains of V⁵⁺O₅ tetragonal pyramids. These chains running along the c- and a-axes, respectively, link, forming an open framework with Cs ions in the voids. At elevated temperatures, the temperature dependence of dc magnetic susceptibility evidences a Haldane-type behavior with estimated intrachain exchange interaction J = 267 ± 16.5 K followed by the strong upturn at lower temperatures. Both dc and ac magnetic susceptibilities exhibit a sharp peak at low temperatures; the latter is independent of frequency. The position of the peak in Fisher's specific heat d(χT)/dT coincides with that in specific heat C_p, which defines the Neel temperature T_N = 5.6 ± 0.2 K. While the values of the calculated interchain exchange interaction J' and single-ion anisotropy D place this system into the Haldane sector of the Sakai-Takahashi phase diagram, the long-range antiferromagnetic order at low temperatures is induced by the defects/impurities.