Abstract
We report measurements of the thermoelectric power (TEP) on the La0.65Ca0.35Mn1-xFexO3 system for 0.00 less than or equal to x less than or equal to 0.07. The ferromagnetic and metallic transition temperatures are lowered and the TEP shows an increasingly positive trend with the addition of Fe. We also observe a clear magnetic contribution that manifests itself as a peak in the TEP close to the critical temperature. The activation energies determined from the TEP are seen to be insensitive to the Fe content. The data are interpreted firstly as showing a decrease in the density of active holes, i.e. holes that can participate in the hopping process, with increasing Fe content. Secondly the data suggest the role of magnetic scattering due to the clusters formed by the antiferromagnetically coupled Fe. Abrupt changes in the variation of the TEP are observed at the concentration region x similar to 0.04 consistent with the hole density variation and with previously reported transport and magnetic measurements.