Electrical transport properties of sintered granular manganite/insulator systems

摘要

Magnetic, structural and transport measurements on granular La0.7Sr0.3Mn3(1-x)Insulator(x) pellets were carried out. The system displayed a conduction threshold at x > 30, i.e.. for a La0.7Sr0.3MnO3 volume fraction X-FM similar to 70. Beyond this value, the resistivity increased steeply, setting up a rather insulating behavior. Nevertheless, the maximum enhancement in magnetoresistance was observed at a concentration x = x(c) similar to 10 at low temperatures and similar to 20 at room temperature. This result was demonstrated to be independent of the applied magnetic field strength. The observed magnetoresistance enhancement seemed to be consistent with the disorder-driven amplification of spin-dependent transport at the structural boundaries of the mixture, due to the presence of the insulating material within the ferromagnetic matrix. (C) 2007 Elsevier Ltd. All rights reserved.