Antiferromagnetic quaternary chalco-halide Ba-3(FeS4)I with long FeMIDLINE HORIZONTAL ELLIPSISFe distances

A novel quaternary chalco-halide Ba-3(FeS4)I was successfully synthesized via a molten salt method. The Ba-3(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. Ba-3(FeS4)I is a semiconductor with a direct band gap of 1.65 eV. Despite the large FeMIDLINE HORIZONTAL ELLIPSISFe separation (>= 6.293 angstrom), the Ba-3(FeS4)I shows unexpected antiferromagnetic ordering with Neel 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-SMIDLINE HORIZONTAL ELLIPSISS-Fe super-super exchange, was found to be responsible for this antiferromagnetic phase transition.