Antiferromagnetic Order and Spin-Canting Transition in the Corrugated Square Net Compound Cu₃(TeO₄)(SO₄)·H₂O

Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquids, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner-sharing square-planar CuO₄ units have been intensely studied due to their Mott insulating ground state, which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid-state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate, Cu₃(TeO₄)(SO₄)·H₂O, a promising alternative to layered perovskites. The orthorhombic phase (space group Pnma) is made of corrugated layers of corner-sharing CuO₄ square-planar units that are edge-shared with TeO₄ units. The layers are linked by slabs of corner-sharing CuO₄ and SO₄. Using both the bond valence sum analysis and magnetization data, we find purely Cu²⁺ ions within the layers but a mixed valence of Cu²⁺/Cu⁺ between the layers. Cu₃(TeO₄)(SO₄)·H₂O undergoes an antiferromagnetic transition at T_N = 67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at T^* = 12 K, evidenced by a kink in the heat capacity. The spin-canting transition is explained on the basis of a J₁-J₂ model of magnetic interactions, which is consistent with the slightly different in-plane superexchange paths. We present Cu₃(TeO₄)(SO₄)·H₂O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.