Crystal structure and magnetic properties of UFe3Al9

The ternary compound UFe3Al9 was synthesized by arc melting, followed by annealing at 850 °C. The crystal structure was determined by single-crystal X-ray diffraction and refined down to a residual value of R=0.043 (RW=0.099, S=0.89), with lattice parameters a=8.8373(2)Å and c=5.0738(2)Å. This phase is a new boundary composition in the extended range of solubility with general formula UFexAl12−x crystallizing in the tetragonal ThMn12-type structure, space group I4/mmm, with the iron atoms partially occupying the equivalent 8f positions. AC-susceptibility and magnetization measurements seem suggestive of a ferromagnetic type of transition at T≈25K, but specific heat and 57Fe Mössbauer data indicate that neither long-range magnetic ordering nor standard spin-glass behaviour is associated with the magnetic anomaly. The presence of few iron-rich clusters with short-range ferromagnetic-like order at low temperatures is proposed for UFe3Al9.