Effects of phonon hardening on the polaron transport in colossal magnetoresistive manganites

Abstract

It is well established that transport properties of colossal magnetoresistive manganites can be qualitatively explained by the small polaron model incorporating the double-exchange interaction. We have improved this model by taking into account effects of phonon frequency hardening below T-c. It is found that the effects are significant in that the resistivity drop for T < T-c becomes much steeper and the magnetoresistance is enhanced substantially at T-c in accord with experiments. This model is applied to understand the evolution of T-c with the chemical pressure in R(0.7)A(0.3)MnO(3) series.