Physical properties of the new Kagome metal UNb₆Sn₆

The electronic band structure of hexagonal Kagome materials is predicted to contain coexisting flat bands, van Hove singularities, and Dirac points. Materials in the hexagonal RM₆X₆ (166) family (R=rare-earth, M=transition metal, X=Ge, Sn) contain Kagome nets of transition metal ions and are of particular interest because their chemical tunability enables access to these interesting band structure features and to novel ground states. Substitution of an actinide element on the rare-earth site in the 166 family is underexplored. We successfully synthesized single crystals of UNb₆Sn₆. We probed the physical properties of UNb₆Sn₆ with x-ray and neutron diffraction, magnetic susceptibility, electrical resistivity, and heat capacity. We found a complex magnetic field-temperature phase diagram, with at least five different magnetic phases and two zero-field magnetic transitions (T_N=46 K, T₂=42 K). Neutron and x-ray diffraction measurements point to deviations from the ideal hexagonal P6/mmm structure, a feature often observed in the 166 family due to the large M-X cage-like voids in the structure.