Evidence for persistent spin fluctuations in uranium sesquicarbide

The low-temperature magnetic susceptibility, heat capacity and electrical resistivity of uranium sesquicarbide have been estimated down to 2 K by combining measurements carried out on samples of U2C3, containing UC as minority phase, and on pure UC specimens. The presence of spin fluctuations with characteristic temperature TSF = 7 K is revealed by a nonanalytic contribution to the specific heat behaving (well below TSF ) as T3ln(T=TSF), and confirmed by a T2 increase of the electrical resistivity and a 1 κT2 decrease of the low-temperature magnetic susceptibility. The analysis of the specific heat data above TSF provides a Debye temperature ΘD ≈ 256 K and a moderately high value of the Sommerfeld coefficient, γ 42.4 mJmol -1 U K -2. The zero-temperature many-body enhancement of the electron mass is found to be m *m ≈ 2.7. Our data rule out the occurrence of magnetic ordering in U2C3. First principles electronic structure calculations support the absence of a magnetically ordered ground state but suggest that dynamical spin fluctuations are responsible for the electron mass enhancement.JRC.E.6-Actinide researc