Electrical properties and enhanced room temperature magnetoresistance in (La0.7Ca0.2Sr0.1MnO3)1-x/Pdx composites

The structural, electrical, magnetic, and magnetoresistance (MR) properties for perovskite (1 - x)La0.7Ca0.2Sr0.1MnO3 (LCSMO)/Pdx have been studied in this present work. The results of X-ray diffraction, scanning electron microscopy and magnetic measurement indicate that no reaction occurs between LCSMO and Pd grains, and that Pd segregates mostly at the grain boundaries of LCSMO. Pd addition has a little influence on the Curie temperature (TC), but it decreases the resistivity (ρ) dramatically and shifts the metal-insulator transition temperature (Tp) towards a higher value substantially. In the low-temperature ferromagnetic (FM) metallic region the ρ data follow an empirical relation, ρ = ρ0 + ρ2.5T2.5 + ρ7.5T7.5, reflecting that the conductive mechanism mainly arises from electron-electron, electron-phonon, and electron-magnon scattering. But in the high-temperature paramagnetic (PM) semiconductor region, the ρ data for all samples follow the adiabatic small-polaron-hopping model. Moreover, the ρ-T curves for all samples can be fitted well to a phenomenological model derived from spin-polarized tunneling at grain boundaries and a thermal activation. This result suggests a coexistence of FM clusters and PM regions near TC and indicates the prominent intrinsic behaviors of the LCSMO matrix. It is very interesting to note that the MR at room temperature is enhanced, which is encouraging for potential applications.