Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

Electrical resistivity $\rho$, specific heat C, and magnetic susceptibility $\chi$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $\rho$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $\chi$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.Comment: 18 pages, 5 figure

Anomalous rattling and single crystalline properties of the caged compound URu2Al10

International audienceWe report on an experimental single-crystal study of URu2Al10, crystallizing in the YbFe2Al10 type orthorhombic structure, supplemented by the results of crystal field and band structure calculations. We investigated the magnetic, thermal and transport properties of this caged-type compound. Based on the local character of the 5f 2−electron configuration of the U4+ ion in URu2Al10, the effective crystal field (CF) potential in the intermediate coupling form was estimated using the CF level scheme, composed only of singlets. This was carried out in a similar manner to that reported for UFe2Al10 [Phys. Rev. B 92 (2015) 104427]. The obtained scheme satisfactorily reproduces both the magnetic susceptibility (measured along the three main crystallographic directions) and the Schottky-type anomaly of the specific heat. The latter was estimated using the specific heat data of ThRu2Al10 as a phonon reference. In addition, the strong anisotropic behavior of the Seebeck coefficient measured along the three principal directions, and its low-temperature pronounced maxima, have been approximately explained by the CF effect. The latter dominates in the S-shaped temperature dependencies of the electrical resistivity, measured using the current flowing along the three main axes. However, the magnetoresistivity reveals an anisotropic electronic structure that could originate from a c-f hybridization effect in an orthorhombic unit cell. This gives rise to the typical metallic character of URu2Al10, as is also the case for UFe2Al10. This behavior underlines the dual character of the 5f–electrons in these ternaries. In turn, the presence of low-frequency Einstein modes reflects the presence of regular rattling of the U4+ ion located in the [Ru4Al16] cage. This rattling is, however, disturbed at low temperatures by applying an external magnetic field which causes strong scattering of the experimental electrical resistivity points. This effect is also anisotropic, as proved by a comparison of the resistivity results determined at zero and 9 T for a single-crystalline sample of URu2Al10. The above effect also exists for isostructural UFe2Al10, but its anisotropy is less apparent. © 2018 Elsevier B.V

Magnetism and magnetotransport of cage-type compound UOs2Al10

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Comparative studies of the cage systems ThFe2Al10 and UFe2Al10

International audienceWe have grown single crystals of ThFe2Al10 and used them for the refinement of its crystal structure. From the specific heat data, we determined the phonon components, that is, the Debye and Einstein modes, for Th- and U-based isostructural aluminides. To approximate the Sommerfeld coefficients, we had to include the T3lnT term characteristic of spin-fluctuations originating from the Fe-sublattice. The roughly estimated spin-fluctuation temperature is about 11 K. ThFe2Al10 is a weakly temperature-dependent Pauli-paramagnet. However, at lower temperatures the ferromagnetic correlations are observed, which signals that the system drives to quantum criticality. The distinct minimum in electrical resistivity observed at about 20 K suggests a realization of a nonmagnetic two-channel Kondo-effect in ThFe2Al10, as discussed for ThAsSe [Phys. Rev. Lett. 94, 236603 (2005)], for example. The [ρ(T) – ρmin] versus T curves of ThFe2Al10, determined along the a- and c-axes, were used to subtract the phonon contributions from the corresponding ρ(T)a,c of UFe2Al10. The resulting magnetic part of the average ρm(T)av curve was then analysed in terms of the influence of the crystal field effect on the transport properties. However, to obtain agreement with the experiment, we had to take into account another effect, namely the Kondo-like one. This kind of probe has been applied for the first time in the case of uranium compounds. Based on the magnetoresistivity, we have revealed the anisotropic low-frequency vibrations of the Th atom (located in its [Al16Fe4] cage) interacting with the conduction band, the phenomenon revealed previously in the metallic UB12 [Phil. Mag. B 95, 2343 (2015)]. Furthermore, fully relativistic band structure calculations performed for ThFe2Al10 revealed its metallic-like character with a similarly large contribution of the Fe 3d electrons at the Fermi level as predicted previously for its 5f-electron analogue UFe2Al10. In addition, there are substantial differences between their Fermi surfaces