Temperature and doping dependence of the thermopower in LaMnO₃

Abstract

The temperature dependence of the thermopower ( S ) for La_1−x A_x MnO₃ ( A = 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 S₀ + S_{3 / 2}T^3/2+ S₄ T⁴ over a wide range of temperature and doping. The coefficients S₀ , S_3/2 , and S₄ 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.