Transport and magnetic properties of La0.7Pb0.3MnO3+x Ag (x=0−20 wt %) nanocomposites

Abstract

Magnetization and transport properties of La0.7Pb0.3MnO3+x Ag (x=0−20 wt %) nanocomposites have been reported. In this Ag-containing colossal magnetoresistive (CMR) La0.7Pb0.3MnO3 composite (referred to as CMR-Ag), conductivity (σ) and metal–insulator transition temperature (Tp) increase with increasing Ag. Electron microscopy and elemental mapping indicated a uniform distribution of Ag nanoparticles/clusters. The enhancement of Tp is accompanied by a reduction of the c-axis lattice constant. Coexistence of interfacial tunneling with intrinsic transport behavior has been observed at the grain boundaries in the samples with a higher (⩾10 wt %) Ag content. Due to the presence of nonmagnetic Ag in the ferromagnetic La0.7Pb0.3MnO3 material, dc magnetization decreases but the corresponding Tp increases. In the low-temperature (T<Tp) phase, resistivity data follow a T2 dependent behavior for the samples with higher Ag concentration (x⩽5 wt %). On the other hand, for lower Ag (⩽5 wt %) containing samples, a T2.5 dependent behavior is observed. This suggests the importance of both the electron–electron (T2 dependence behavior) and the electron–magnon (T2.5 dependence behavior) interactions for explaining low-temperature (T<Tp) transport data of the CMR-Ag nanocomposites. In the insulating (semiconducting) regime (T>Tp), conductivity data follow the adiabatic polaron hopping conduction mechanism. Unlike the Ag free sample, the variable-range-hopping model is found to be inapplicable for the present Ag containing nanocomposites.