Electrical and thermal transport properties of the electron-doped manganites La0.9-xY(Ho)xTe0.1MnO3

Systematical studies of resistivity ρ(T), thermopower S(T), and thermal conduction κ(T) have been performed on the electron-doped manganites La0.9-xAxTe0.1MnO3 (A=Y or Ho, 0.05=<x=<0.15). The Y005, Y010, Ho005 and Ho010 samples exhibit double insulator-metal (I-M) transitions in the ρ(T) curves, one is very close to its Curie temperature TC, the other is well below TC. However, the Y015 and Ho015 samples present insulating behaviors in the whole measured temperature. S shows positive sign for all samples with a peak near TC and a bump/peak in the ferromagnetic (FM) region. The ρ(T) and S(T) data above TC can be fitted well by the variable-range hopping (VRH) model. The small thermal conduction data suggests that there exists a large JT distortion in the studied samples. Moreover, comparing with the Y-doped compounds, the Ho-doped ones have smaller the thermal conduction value. This result is discussed as the existence of antiferromagnetic (AFM) coupling between Ho and Mn ions in the Ho-doping samples. On the one hand, the magnetic disorder enhancement due to the competition of ferromagnetic (FM) and AFM lower the thermal conductivity, on the other hand, the AFM coupling will reduce the phonon-phonon scattering