Point-contact spectroscopy measurements have been performed on the R_3Pd_{20}X_6 (R = La, Ce; X = Si, Ge) cage compounds. In case of La the characteristic phonon energies have been obtained in agreement with that of the Raman scattering. In Ce_3Pd_{20}Si_6 we have observed asymmetric behaviour of dV/dI(V) dependences which was observed in non-Fermi liquid compound. In Ce_3Pd_{20}Ge_6 we have observed maxima at crystalline electric field energies, influenced by magnetic field. This is connected with quadrupolar ordering transition.
An investigation of the magnetic heat capacity of the heavy-fermion compound YbCu_4Ni up to 0.4 K is presented. The novel compound LuCu_4Ni, isotypic with YbCu_4Ni has been synthesized and characterized, and its heat capacity was measured in order to subtract the lattice contribution from the previously measured heat capacity data of YbCu_4Ni.
The results on the influence of magnetic field on the electrical resistivity ρ(T) of the heavy fermion YbCu_4Ni in the temperature range 0.4-300 K are presented. We have observed a Kondo-like behaviour below 10 K with a minimum in ρ(T) at about 60 K. An applied magnetic field depresses this behaviour, and a maximum in ρ(T) appears similarly to the maximum observed in heat capacity. The observed electrical magnetoresistance shows negative values in all applied magnetic fields and with increasing temperature its absolute magnitude increases. Moreover, we extended our previous susceptibility measurements up to high temperatures of 1000 K, in order to study possible mixed valence behaviour, which however was not observed.
Heat capacity measurements performed on the new ternary compound YbCu_4Ni indicate for this compound strong electronic correlations with possible antiferromagnetic phase transition below 0.5 K. Susceptibility and magnetisation measurements above 2 K show no magnetic ordering.
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