Crystal Structure and Magnetic Properties of the Quasi-One-Dimensional Quantum Spin System Cu₂Cl₄·H₈C₄SO₂

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The crystal structure of Cu₂Cl₄·H₈C₄SO₂ was analyzed by single-crystal X-ray diffraction. This compound consists of the double chain of the edge-sharing octahedra CuCl₅O. With decreasing temperature, the magnetic susceptibility decreases steeply toward zero below 10 K after exhibiting a broad maximum at 65 K, which is characteristic of the one-dimensional antiferromagnet. The magnetic properties of the present system can be described by the double spin chain model with dominant exchange interactions along the leg. The observed small excitation gap Δ⁄k_B≈5.8 K is attributed to the weak exchange alternation along the leg or the weak zig-zag rung interactions. The magnetization curve measured at 1.3 K for the magnetic field parallel to the c-axis shows a discontinuous jump at H_t≈22.8 T indicative of the phase transition of the first order.