SrMnGeS₄: A Two-Dimensional Layered Chalcogenide with Magnetic Triangular Lattice

Two-dimensional (2D) magnetic triangular systems are of great interest due to quantum phenomena, but most are occasionally synthesized. In this study, by using the structure building unit of GeS₄ tetrahedron, a novel 2D chalcogenide SrMnGeS₄ with triangular lattice has been successfully synthesized. The title compound features a layered magnetic triangular lattice of Mn²⁺ ions connected by GeS₄ tetrahedron units, which are further separated by nonmagnetic Sr²⁺ ions. Magnetic measurement results indicate a large Weiss temperature of -67.5(2) K for a strong dominant antiferromagnetic interaction, compared to those of its isostructure BaMnSnS₄ and other magnetic chalcogenides. These are confirmed by our DFT + U calculation results, which also suggest that the triangular layer of SrMnGeS₄ and BaMnSnS₄ could be further simplified by a triangular chain lattice and the triangular chains of adjacent layers interact strongly to finally form a three-dimensional spin lattice. Accordingly, a long-range order is experimentally observed at 22 K. Magnetization measurements for SrMnGeS₄ indicate a spin flop behavior around 1.5 T, and its magnetization at 7 T is 0.55 μ_B, further confirming that antiferromagnetic interactions are strong. Our work illustrates that the use of tetrahedral units like GeS₄ offers a promising strategy to design and construct magnetic frustrated lattices.