Spin polarization and transport in the manganite La0.85Te0.15Mn0.9Cu0.1O3

The resistivity ρ(T), and thermoelectric power (TEP) S(T,H) in the manganite La0.85Te0.15Mn0.9Cu0.1O3 have been investigated systematically in the absence and presence of magnetic fields. A large negative magnetoresistance (MR) appears up to 5 T. In addition, S(T) of the sample shows an anomalous peak, which is suggested to be related to the contribution of phonon drag. Particularly, the thermally induced and the field-induced sign change of S below the Curie temperature TC is observed, implying the importance of spin polarization. In terms of the change of electronic structure, the orbital degree of freedom of the eg carriers can be responsible for the effective lifting of the degenerate eg band. Additionally, based on the fitting results of ρ(T) and S(T), the transport mechanism for the sample in the paramagnetic (PM) insulting region and low-temperature ferromagnetic (FM) insulating region below TC is suggested to be dominated by variable-range-hopping (VRH) conduction. However, in the intermediate-temperature FM metallic region below TC, the transport mechanism is considered to be dominated mainly electron-magnon scattering.