Antiferromagnetic quaternary chalco-halide Ba3(FeS4)I with long Fe⋯Fe distances

Abstract

A novel quaternary chalco-halide Ba₃(FeS₄)I was successfully synthesized via a molten salt method. The Ba₃(FeS₄)I crystallizes in the orthorhombic space group Cmcm (NO. 63). It features two dimensional [Ba₃I]⁵⁺ layers, which are separated by isolated [FeS₄]⁵⁻ tetrahedra. Ba₃(FeS₄)I is a semiconductor with a direct band gap of 1.65 eV. Despite the large Fe⋯Fe separation (≥6.293 Å), the Ba₃(FeS₄)I shows unexpected antiferromagnetic ordering with Néel temperatures (T_N) of 108 K. The possible magnetic structures and the underlying magnetic interaction mechanism were proposed based on the first-principles electronic structure calculations. The [FeS₄]⁵⁻ tetrahedra behave like super-moments due to the strong p–d hybridization between Fe and S, making the S atoms adopt the same spin orientation to their nearest-neighboring Fe atoms. The new magnetic interaction mechanism, namely the Fe–S⋯S–Fe super–super exchange, was found to be responsible for this antiferromagnetic phase transition.