Synthesis, structure and physical properties of the new uranium ternary phase U3Co2Ge7

A new ternary compound, U3Co2Ge7, has been synthesized from the corresponding elements by a high temperature reaction using molten tin flux. It crystallizes in the orthorhombic La3Co2Sn7-type (Pearson's symbol oC24, space group Cmmm, No. 65) with lattice parameters determined from single-crystal X-ray diffraction as follows: a=4.145(2) Å; b=24.920(7); c=4.136(2) Å, V=427.2(3) Å3. Structure refinements confirm an ordered structure having two crystallographically inequivalent uranium atoms, occupying sites with dissimilar coordination. U3Co2Ge7 orders ferromagnetically below 40 K and undergoes a consecutive magnetic transition at 20 K. These results have been obtained from temperature- and field-dependent magnetization, resistivity and heat-capacity measurements. The estimated Sommerfeld coefficient γ=87 mJ/mol-U K2 suggests U3Co2Ge7 to be a moderately heavy-fermion material.

Graphical abstractA new uranium compound, U3Co2Ge7 has been synthesized and structurally characterized. The close structural relationship between the orthorhombic structure of U3Co2Ge7 and the tetragonal structure of U3Co4Ge7 is emphasized. U3Co2Ge7 is a moderate heavy-fermion ferromagnet (or ferrimagnet) at 40 K that undergoes another transition at 20 K.Figure optionsDownload full-size imageDownload as PowerPoint slide