New insight on the properties of the superconducting iron spin ladder BaFe<sub>2</sub>S<sub>3</sub>

BaFe2S3 and BaFe2Se3 are the only two quasi-one-dimensional iron-based compounds that become superconductors under pressure. Interestingly, these two compounds exhibit different symmetries and properties. While more detailed and recent studies on BaFe2Se3 using single crystals have advanced the field towards a more universal description of this family, such a study is still lacking for the compound BaFe2S3. Here, we present a detailed study of the crystalline and magnetic structures performed on single crystals using X-ray and neutron diffraction. We demonstrate a polar structure at room temperature within the Cm2m space group, followed by a structural transition at TS = 130 K to the polar Pb21m space group. This space group remains unchanged across the magnetic transition at TN = 95 K, revealing multiferroic characteristics with a weak magnetoelastic coupling. The determined magnetic structure is monoclinic (Pam), with non-collinear Fe magnetic moments, tilted from the rung axis. This reexamination of the temperature-dependent properties of BaFe2S3 provides new insights into the physics of this system from multiple key perspectives.