Structural and magnetic properties of UFe6Ga6

UFe₆Ga₆ polycrystalline samples were prepared by arc-melting, and single crystals were grown by the Czochralski method. This compound crystallizes in the orthorhombic ScFe₆Ga₆-type structure (space group Immm, a=5.0560(4), b=8.5484(7) and c=8.6914(7) Å), an ordered variant of the ThMn₁₂-type structure. A ferromagnetic-type transition at T_C=530(5) K is seen in the magnetization and A.C.-susceptibility measurements, and no other magnetic anomaly is observed down to 5 K. Single crystal magnetization measurements along the three different crystallographic axes indicated a as the easy direction, with a spontaneous magnetization M_S=12.3 μ_B/f.u. at 5 K. The analysis of the ⁵⁷Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, B_hf, significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFe_xAl_12−x, where the average B_hf were found to increase with the iron–iron interatomic distances.