Coexistence of localized and itinerant carriers near T-C in calcium-doped manganites

We explore the possibility that polaronic distortions in the paramagnetic p hase of La0.67Ca0.33MnO3 manganites persist in the ferromagnetic phase by c onsidering the observed electrical resistivity to arise from coexisting fie ld- and temperature-dependent polaronic and band-electron fractions. We use an effective medium approach to compute the total resistivity of the two-c omponent system, and find that a limit with low percolation threshold expla ins the data rather well. To test the validity of this model, we apply it t o the thermoelectric coefficient. We propose a plausible mean-field model t hat reproduces the essential features of a microscopic model and provides a comparison with the experimental mixing fraction, as well as the magnetiza tion and magnetic susceptibility.