Flux-Driven Order–Disorder Polymorphs of Kagome SmFe6Ge6

Abstract

While polymorphism in kagome-derived intermetallics offers a powerful route to controlling structure–property relationships, it still remains poorly explored for many rare-earth members due to synthetic constraints. Here, we report the discovery and controlled growth of two previously unreported polymorphs of SmFe6Ge6 adopting an orthorhombic structure (space group Immm), realized in both ordered and disordered variants. Differential scanning calorimetry (DSC) was employed to identify critical thermal events, enabling the development of targeted flux-growth conditions that selectively stabilize each polymorph. High-quality single crystals were obtained and structurally characterized by single crystal and powder X-ray diffraction, revealing differences in Sm-site ordering within the same crystallographic framework. X-ray absorption spectroscopy confirms the Sm valence state of 3+. Anisotropic magnetic measurements performed on oriented single crystals demonstrate pronounced directional dependence of the magnetic response, while 57Fe Mössbauer spectroscopy revealed that the Fe sublattice participates in at least two field-induced metamagnetic transitions yielding phases with sizable canting of Fe moments. These results establish flux chemistry, guided by thermal analysis, as a decisive parameter for directing polymorph selection and crystallographic order in rare-earth kagome systems, expanding the accessible structural landscape of AM6X6 materials.