The crystal and magnetic structures of UFexAl12-x alloys

Powdered samples of UFexAl12-x (x = 4, 5 and 6) systems have been measured by means of magnetization, Mossbauer effect, X-ray and neutron diffraction techniques in the temperature range 1.5-400 K. The f-sites in all samples are occupied by iron. Excess iron atoms in samples with x = 5 and 6 are located at j-sites only. The ordering of iron in UFe4Al8 is antiferromagnetic with the iron moment perpendicular to the c-axis. No magnetic moment is seen on U atoms down to 1.5 K, The samples UFe5Al7 and UFe6Al6 exhibit in general a ferromagnetic behaviour. An ordered magnetic moment in the U sublattice is seen in UFe5Al7 only. The Mossbauer spectra suggest that iron magnetic moments at j- and f- sites are only slightly different.