Temperature and doping dependence of the thermopower inLaMnO3

The temperature dependence of the thermopower $(S)$ for ${\mathrm{La}}_{1\ensuremath{-}x}{A}_{x}{\mathrm{MnO}}_{3}$ $(\mathrm{A}\phantom{\rule{0ex}{0ex}}=\mathrm{Sr},$ Ba, Pb, and Ca) perovskites has been investigated systematically as a function of doping $(x)$ in order to determine the role of several scattering mechanisms in the ferromagnetic phase. Irrespective of the nature of $A$ ions, the thermopower shows strong temperature dependence and can be positive or negative depending on the doping level and temperature. In the ferromagnetic regime, thermopower follows an expression of the form ${S}_{0}{+S}_{3/2}{T}^{3/2}{+S}_{4}{T}^{4}$ over a wide range of temperature and doping. The coefficients ${S}_{0}{,S}_{3/2},$ and ${S}_{4}$ show systematic variation with the doping concentration. The large peak well below the ferromagnetic transition ${(T}_{c})$ and the complicated temperature dependence of $S$ may be understood on the basis of electron-magnon scattering as predicted for an itinerant ferromagnet.