Crystal structure and anisotropic magnetic properties of CaCo₄(TeO₃)₄Cl₂

We report on the discovery and the magnetic properties of CaCo₄(TeO₃)₄Cl₂. Single-crystal X-ray diffraction shows that this compound crystallizes on a monoclinic lattice, in the space group C2/c with a = 19.869(1) Å b = 5.323(1) Å c = 16.965(1) Å and β = 125.091(1)°. The compound has a layered structure that additionally exhibits 1D structural motifs composed of staircase-like double chains of magnetic face- and corner-sharing [CoO₅Cl] and [CoO₆] octahedra, which are linked by Ca²⁺ ions and [TeO₃]^{2 –} units. Temperature-dependent magnetic measurements reveal antiferromagnetic (AFM) ordering with a Néel temperature of T_N ≈ 11.5 K and an effective moment of μ_eff ≈ 5.2 μ_B/Co consistent with expectations for Co²⁺ high spin. The Curie-Weiss temperature θ ≈ –42.1 K indicates AFM interactions dominate between the magnetic moments. The magnetic ordering transition in the zero-field heat capacity shows a λ-type anomaly. Direction-dependent magnetic measurements on single-crystals reveal an anisotropic character of the magnetization. For H || c — corresponding to a direction within the layers and perpendicular to the double chains — the AFM transition temperature is suppressed in magnetic fields higher than ~ 7.9 T and a clearly pronounced metamagnetic phase transition is observed.