X-RAY AND NEUTRON POWDER DIFFRACTION STUDIES OF UIRGE AND UAUGA

The crystal and/or magnetic structures of UIrGe and UAuGa have been in vestigated by means of X-ray and neutron powder diffraction measuremen ts. UIrGe exhibits an orthorhombic TiNiSi-type structure (space group Pnma); no magnetic order at low temperature is observed with neutrons for UIrGe. The crystal structure of UAuGa is orthorhombic, but due to nearly identical Au and Ga neutron scattering amplitudes, we are not a ble to select either the ordered TiNiSi-type or the disordered CeCu2-t ype structure. At low temperature, UAuGa is antiferromagnetic: the str ucture is collinear, with uranium magnetic moments parallel to the ort horhombic c-axis. At T = 7 K, the uranium magnetic moment is equal to 1.35(5) mu(B).