Crystal structure and electronic properties of the new compound U3Fe4Ge4

The new ternary compound U3Fe4Ge4 was prepared by melting the pure metals in the stoichiometric ratio. An ingot of large scale domain was obtained by decreasing the temperature from the liquid state down to 1000 °C over 4 h. Single crystal X-ray diffraction revealed that U3Fe4Ge4 crystallizes with the Gd3Cu4Ge4-type of structure, in the orthorhombic space group Immm (no. 71), Z = 2, with unit-cell parameters at room temperature of, a = 4.090(1) Å, b = 6.639(1) Å and c = 13.702(1) Å. The crystal structure is characterized by two U, one Fe and two Ge independent crystallographic positions and can be described as resulting from the condensation by face-sharing and edge-sharing of U(1)Ge6 octahedrons, U(2)Ge6 trigonal prisms and Fe(1)Ge4 tetrahedrons. The electronic properties of this new compound were investigated by means of electrical resistivity, thermopower, ac and dc magnetic susceptibility and 57Fe Mossbauer spectroscopy. U3Fe4Ge4 undergoes a ferromagnetic transition below TC = 17(1) K. The low temperature (4 K) 57Fe Mossbauer spectra can be well fitted using a model with Fe atoms in a paramagnetic state, suggesting that the magnetic ordering originates from the U sublattice alone.

Graphical abstractThe electronic properties of the new compound U3Fe4Ge4 suggest a change of behaviour of the 5f electrons from a localized-like character at high temperature to a fairly delocalized behaviour at low temperature.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Novel uranium intermetallic compound. ► Ferromagnetic ordering at low temperature. ► Itinerant system at low temperature. ► Strong hybridization between the U 5f and Fe 3d electrons.