Transport properties of Ce2Ni2Sn and Ce2Pd2.05Sn0.95 Kondo lattice systems

We report experimental data on thermoelectric power S, electrical resistivity ρ, and the magnetoresistivity of the antiferromagnet Kondo stannides Ce2Ni2Sn (TN=4.7 K) and Ce2Pd2.05Sn0.95 (TN=4.7 K). The essential features of the S(T) curves resemble those of heavy fermion systems such as CeCu2Si2: a broad and positive maximum at intermediate temperatures, followed by a sharper negative minimum at lower temperatures. S values are is considerably smaller in Ce2Pd2.05Sn0.95 than in Ce2Ni2Sn. The positive peak originates from the incoherent Kondo scattering by the excited crystal field levels of the Ce ion ground state. The negative peak might be related to the shape of the density of states associated with the Abrikosov–Suhl resonance. The change of sign in S(T) between its minimum and maximum at T* can be assigned to the fact that the Fermi level sinks below the upper band at T>T*. This behavior and the maximum observed in the ρ(T) curve at this temperature can be discussed in terms of the electron polaron model, although one must also take into account the crystal field effect. The role played by the crystal field effect, which is more important in Ce2Pd2.05Sn0.95, is analyzed for this compound, providing the magnitude of the crystal field splitting. Magnetoresistivity was also measured in both compounds. The results are consistent with the important role of the Kondo effect at low temperatures and suggest the splitting of the double degenerate bands at T>T*.