Crystal Structure and Low-Dimensional Magnetism in CsNiV₂O₆Cl

Single crystals of CsNiV₂O₆Cl were grown hydrothermally. Its crystal structure (space group <i>I</i>2̅<i>/a</i>) 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 <i>c-</i> and <i>a</i>-axes, respectively, link, forming an open framework with Cs ions in the voids. At elevated temperatures, the temperature dependence of <i>dc</i> magnetic susceptibility evidences a Haldane-type behavior with estimated intrachain exchange interaction <i>J</i> = 267 ± 16.5 K followed by the strong upturn at lower temperatures. Both <i>dc</i> and <i>ac</i> 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<i>(χT)/</i>d<i>T</i> coincides with that in specific heat <i>C</i>_p, which defines the Neel temperature <i>T</i>_N = 5.6 ± 0.2 K. While the values of the calculated interchain exchange interaction <i>J'</i> and single-ion anisotropy <i>D</i> 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.