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 TC=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 MS=12.3 μB/f.u. at 5 K. The analysis of the 57Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, Bhf, significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFexAl12−x, where the average Bhf were found to increase with the iron-iron interatomic distances.