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

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 (sigma) and metal-insulator transition temperature (T-p) increase with increasing Ag. Electron microscopy and elemental mapping indicated a uniform distribution of Ag nanoparticles/clusters. The enhancement of T-p 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 (greater than or equal to10 wt %) Ag content. Due to the presence of nonmagnetic Ag in the ferromagnetic La0.7Pb0.3MnO3 material, dc magnetization decreases but the corresponding T-p increases. In the low-temperature (T<T-p) phase, resistivity data follow a T-2 dependent behavior for the samples with higher Ag concentration (xless than or equal to5 wt %). On the other hand, for lower Ag (less than or equal to5 wt %) containing samples, a T-2.5 dependent behavior is observed. This suggests the importance of both the electron-electron (T-2 dependence behavior) and the electron-magnon (T-2.5 dependence behavior) interactions for explaining low-temperature (T<T-p) transport data of the CMR-Ag nanocomposites. In the insulating (semiconducting) regime (T>T-p), 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. (C) 2003 American Institute of Physics.