Intermediate Valence Model for Tl₂Mn₂O₇

There have been speculations about the need to find a new mechanism to explain the colossal magnetoresistance exhibited by this material, having pyrochlore structure and thus differing structurally and electronically from the manganites. We will report here our transport results based on a two band model, with conduction electrons and intermediate valence ions fluctuating between two magnetic configurations. The model has been previously employed to understand transport and thermodynamical properties of intermediate valence Tm compounds and, in its periodic version, to analize the phase diagram. The results obtained with this model for the transport properties of Tl_{2}Mn_{2}O_{7} are in good qualitative agreement with the experimental results.