The anomalous temperature variation of the thermoelectric power in the f-electron metallic compounds, namely the sign reversal or the maxima, is sometimes interpreted as resulting from the conduction electrons scattering in Born approximation on the acoustic phonons and on the localized spins in the s-f exchange interaction. The experimenters rely on the results of some theoretical works where such thermoelectric power behavior was obtained within these simple models. In the present paper we prove that neither the electron-phonon scattering nor the magnetic s-f scattering in the Born approximation (nor both of them) do lead to the effects mentioned above.

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The possibility of the occurrence of a maximum in the temperature dependence of the electrical resistivity in the paramagnetic phase of singlet ground state crystal field materials is examined theoretically on the basis of a n earlier developed formalism for a many-level system (PrIn,) and 8 simple two-level model. It is shown that the existence of a weak exchange interaction in paramagnetic PrIn, improves the fitting of the theoretical results to experimental data but the occurrence of the maximum in the temperature dependence of the resistivity in ferromagnetic Pr,TI in a n earlier paper by using the same formalism may be questioned. Further investigations are required to explain the effect. Formulation of the ProblemSince the pioneering oonsiderations of Rao and Wallace [I] effects of the crystal field (CF) splitting on the electrical resistivity of f-electron crystalline systems have been investigated in a number of papers [2]. It has been found that the electrical resistivity, e, of paramagnetic crystals calculated in the first Born approximation exhibits a monotonous increase with temperature, reaching a saturation value (spin disorder resistivity) at a temperature comparable with the overall C P splitting in accordance with most experimental data. and thus the origin of the maxima must be a consequence of another microscopic mechanism. I n [4] it has been demonstrated that exchange interactions between the localized f-shell moments (which are responsible for a ferromagnetic order in Pr3T1 a t low temperatures) and collective excitations in this singlet ground CP system can manifest themselves in the existence of a flat resistivity maximum in the paramagnetic phase.

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