Transport mechanism and magnetothermoelectric power of electron-doped manganites La0.85Te0.15Mn1−xCuxO3 (⩽x⩽0.20)

Abstract

We present the results of a systematic study of the transport mechanism and magnetothermoelectric power (MTEP) of electron-doped manganites La0.85Te0.15Mn1−xCuxO3 (0⩽x⩽0.20). Two peaks are observed in thermoelectric power S(T) curves for x<0.10 samples. For x>0.10 samples, the very large S value with over 100μV∕K at low temperatures appears, which is attributed to the destruction of ferromagnetic (FM) order and the strong carrier localization at low temperatures due to Cu doping. In addition, a sign variation of S(T) for Cu-doped samples is also observed, which may originate from the narrowing of the concomitant σ(eg↑−2p) band. Particularly, an anomalous behavior of S(T) is observed in x=0.10 sample, which is suggested to be related to the contribution of spin polarization and phonon drag. Based on the results of resistivity ρ(T) and S(T), the transport mechanism in the high-temperature paramagnetic region for all the samples and low-temperature FM insulating region below TC for the samples with x⩽0.10 can be described by the variable-range-hopping model. However, in the intermediate-temperature FM metallic region below TC, ρ(T) and S(T) of the samples with x⩽0.10 are well fitted by the formula ρ=ρ0+ρ2.5T2.5 and S=S0+S3∕2T3∕2+S4T4, respectively, implying the importance of electron-magnon scattering. As to the MTEP, only a negative MTEP peak close to TC is observed in the whole measured temperature range for the samples with x>0.10, which is suggested to originate from the spin alignment induced by applied magnetic fields. However, for x⩽0.10 samples, an additional positive MTEP peak is induced by Cu doping below TC besides a large negative MTEP peak in the vicinity of TC, which is ascribed to the enhancement of electron-magnon interaction caused by the Cu doping and the decrease of magnetic entropy around TC, respectively.