Crossover from intrinsic to extrinsic magneto transport in La1-xPbxMnO3 perovskite systems

Abstract

The intrinsic to extrinsic magneto transport of Pb doping and intermediate grinding on transport as well as magnetic properties in La1-xPbxMnO3 (x = 0, 0.15, 0.25 and 0.4) has been investigated. Double exchange related electron transport is supposed to prevail in case of highly doped samples whereas spin dependent interfacial tunneling of conduction electrons along with double exchange related electron transport dominate conduction process in case of less Pb substituted samples. It has been shown that with repeated grinding and increase in doping percentage (within the doping limit), it is possible to have relatively narrow grain size distribution, which is a major cause of gradual disappearance of the intergrain interfacial tunneling (extrinsic) resistance leaving only intragrain (intrinsic) transport properties in the high temperature region. At low temperature the existence of spin-glass insulator behaviour were observed, which get stronger with decrease in Pb content. Thus with decrease in Pb doping, it has been possible to generate relatively wide distribution of grain size with probable increase in misorientation angle in the grain boundary region. This reveal a crossover from major intrinsic to combination of extrinsic, intrinsic magnetotransport and spin-glass behaviour.