Effect of electron/hole doping on the transport properties of lanthanum manganites LaMnO₃

Abstract

We report the results of electrical resistivity, magnetic susceptibility and thermoelectric power measurements on the stoichiometric hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites. The resistivity and thermopower data show a metal-insulator phase transition for both samples. Magnetic susceptibility measurement confirms that both the samples undergo a transition from paramagnetic to ferromagnetic phase at defined Curie temperatures T(c) = 240 K (La(0.8)Ca(0.2)MnO(3)) and 263 K (La(0.8)Ce(0.2)MnO(3)). The electrical resistivity data are then theoretically analysed within the framework of the classical electron-phonon model of resistivity, i.e. the Bloch-Gruneisen model. Detailed analysis of the electrical resistivity of electron- and hole-doped manganites suggests that besides the electron-phonon effect another possibility for the change in carrier density arises due to the presence of electron correlation in the metallic system. From the thermopower S(T) results, we suggest that its behaviour is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the polycrystalline samples of hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites.