Kondo lattice and heavy fermions in Heusler phases: CeInAg2−xCux

Magnetic properties, electrical resistivity, specific heat and magnetic excitations have been investigated in Heusler phases CeInAg_2–xCu_x. The hybridization continuously increases from CeInAg₂ (antiferromagnetic Kondo lattice) to CeInCu₂ (heavy fermion compound). The specific heat coefficient for this last compound is found to reach 1.2 J/mole. K² at 1.4 K, the Kondo temperature is 6 K and the Wilson ratio is close to 2.     

Antiferromagnetic correlations in the cubic heavy fermion compound CeInCu2

CeInCu₂ is a heavy fermion compound close to magnetic instability. The electrical resistivity has aT ² behaviour between 1 and 2.5 K. and the AC field susceptibility has a faint maximum at 0.9 K, indicating the onset of coherence near 1 K for this compound. The magnetoresistance keeps a negative sign down to 0.3 K. Neutron inelastic scattering give a crystal field splitting of 90 K, with a doublet ground state, and a residual quasielastic linewidth of 0.3 meV.We have studied the resistivity, susceptibility and specific heat of some dilute solutions La_1–xCe_xInCu₂ and Y_1–xCe_xInCu₂. The spin-dependent part of the resistivity may be decomposed into a single impurity term plus a pair interaction term, the magnitude of which folows a Curie-Weiss law, as in classical spin glassesCuMn orAuFe.The magnetisation and susceptibility at low temperatures may be represented within the resonant level model, taking into account antiferromagnetic interactions. Finally, the specific heat of CeInCu₂ shows a bump near 2.3 K, absent for dilute solutions, which may also be interpreted by introducing a magnetic interaction term.     

Ground state properties,anisotropy and spin relaxation in diluted Kondo systems Y1-x Ce x Zn

Magnetic susceptibility, magnetization and parastriction measurements are performed on single crystals of Y_1-xCe_xZn solid solutions. The crystal field splitting and the linewidth of magnetic excitations are measured by inelastic neutron scattering; coupling constantsJn(E_F) between 4 electron and conduction band are deduced. Low field susceptibility and parastriction experiments both suggést a 8 ground state. However, the magnetization under high fields and its anisotropy are close to those predicted for a 7 ground state. These contradictions may be attributed to the perturbation of the wave functions of the quartet ground state, due to hybridisation with the conduction band. This occurs since the Kondo temperature is not negligible compared to the crystal field splitting.