The Nernst-Ettingshausen coefficient in hole-doped manganites

Abstract

A systematic study of the Nernst-Ettingshausen coefficient (NEC) in hole-doped manganites of the LaMnO3 and SmMnO3 systems was carried out at temperatures both above and below the point of transition to the magnetically ordered state (Tc). The results obtained for T > Tc suggest that conduction is mediated here by small-radius polarons. For all the compositions studied, the Nernst mobilities at T = 300 K are small (of the order of 0.1–2 cm2/V s) and the carrier relaxation time at T > Tc increases with carrier energy. At temperatures below Tc, the NEC exhibits an anomalous behavior. The giant NEC effect was observed, which consists in a strong dependence of the NEC on applied magnetic field and the presence of a peak in the temperature dependence of the NEC at T ≈ Tc. Near the transition to the magnetically ordered state, the NEC follows a behavior similar to that of colossal magnetoresistance and giant magnetothermoelectric power. A possible origin of the anomalous NEC behavior at T < Tc is discussed.