X-ray diffraction and Mössbauer effect study of site occupation and magnetic properties in UCuxFe5−xAl7 (x=2, 3.5) alloys

X-ray diffraction and Mössbauer effect studies of site occupation in UCu2Fe3Al7 and UCu3.5Fe1.5Al7 were carried out and complemented by magnetic and specific heat measurements in the 2-300 K temperature range and in the 0-9 T magnetic field range. The Rietveld analysis showed that 8i sites were fully occupied by Al, 8f fully occupied by Cu and Fe while the 8j were shared by Cu and/or Fe in addition to three Al atoms per f.u. Knowing also the fraction of 8f and 8j sites occupied by Fe, deduced from room-temperature Mössbauer spectra, it was possible to estimate the Fe, Cu and Al site distribution. Cu was found to have a higher relative preference for 8f sites than Fe. Although the temperature dependence of the specific heat exhibits no anomaly in the 2-300 K temperature range and enhanced values of the coefficient of electronic specific heat are observed (265 mJ/mol K2 for UCu3.5Fe1.5Al7), hyperfine fields observed at 4 K confirm the magnetic order evidenced by the magnetization measurements for both UCu2Fe3Al7 and UCu3.5Fe1.5Al7 and suggest that Cu has nonzero magnetic moment, most probably transferred from the magnetic U or Fe sublattices.