Anomalous transport effects for the metal and insulator doped La0.833K0.167MnO3 systems

► Metal doped and non-metal doped perovskite systems with different grain boundary environments are investigated. ► Contrary transport behaviors for the LKMO/Ag sample and the LKMO/STO sample at the high and low temperature regimes are reported. ► Significant improvement of the room temperature magnetoresistance under low field for the LKMO/Ag sample is observed. ► Different roles of the spin-dependent scattering and the spin-polarized tunneling mechanisms at different temperature regimes are analyzed in detail.