Fe-cluster compounds of chalcogenides: candidates for rare-earth-free permanent magnet and magnetic nodal-line topological material*

Fe-cluster based crystal structures are predicted for chalcogenides Fe₃X₄ (X = S, Se, Te) using adaptive genetic algorithm. Topologically different from the well-studied layered structures of iron chalcogenides, the newly predicted structures consist of Fe clusters which are either separated by the chalcogen atoms or connected via sharing the vertex Fe atoms. Using first-principles calculations, we demonstrate that these structures have competitive or even lower formation energies than the experimentally synthesized Fe₃X₄ compounds and exhibit interesting magnetic and electronic properties. In particular, we show Fe₃Te₄ can be a good candidate for rare-earth free permanent magnet and Fe₃S₄ can be a magnetic nodal-line topological material.