High pressure phase of Ba₂FeS₃: An antiferromagnet with one-dimensional spin chains

In this work, we report on the discovery of the high-pressure phase of Ba₂FeS₃ with quasi one-dimensional (1D) spin chains, which was synthesized under high-pressure and high-temperature conditions. A systematic study was carried out via structural, transport, magnetic and thermodynamic measurements. The high-pressure phase of Ba₂FeS₃ (denoted by Ba₂FeS₃ (HP)) crystallizes in a K₂AgI₃-typed orthorhombic structure with the space group of Pnma (62) and the lattice parameters of a = 8.6831 (1) Å, b = 4.2973 (1) Å, and c = 17.0254 (2) Å, respectively, which consists of chains of corner-sharing FeS₄ tetrahedra along the b axis. Ba₂FeS₃ (HP) undergoes a long-range antiferromagnetic transition at T_N ∼56 K, above which the magnetic susceptibility curve exhibits a round hump behavior with the maximum temperature T_max ∼110 K. In addition, the intrachain coupling J_intra is about −18 K obtained by using the Wagner-Friedberg model. The specific heat data suggest that the total magnetic entropy change ΔS caused by the long-range ordering transition is only ∼20% of the expected value for a S = 2 system. For comparison, the properties of K₂CuCl₃-typed Ba₂FeS₃ with similar quasi 1D spin chains were presented as well. Our results indicate that both compounds exhibit a typical feature expected for compounds with 1D spin chains.