Comparison of the magnetotransport properties between (La0.7Pb0.3MnO3)1−xAgx and (La0.7Pb0.3MnO3)1−x(Fe2O3)x composites

Ceramic composites of (La0.7Pb0.3MnO3)1−xAgx and (La0.7Pb0.3MnO3)1−x(Fe2O3)x are prepared by using chemical and solid-sate sintering route. The structural and magnetotransport properties are studied for these composites. Ferromagnetism is gradually suppressed with the increase of Ag or Fe2O3 mole percentage for both systems. The resistivity decreases significantly for (La0.7Pb0.3MnO3)1−xAgx while resistivity increases dramatically for (La0.7Pb0.3MnO3)1−x(Fe2O3)x. It is suggested that the introduction of Ag into the niche of grain boundaries forms artificial conducting network and improve the carriers to transport. Contrarily, the Fe2O3 in (La0.7Pb0.3MnO3)1−x(Fe2O3)x composite acts as a separation layer between two grains and forms the artificial tunneling junction. However, the enhancement of magnetoresistance has been observed for both systems.