Ferro–antiferromagnetic coupling and enhancement of magnetoresistance in La0.7Ca0.3MnO3/LaMnO3 composites

Abstract

AbstractThe samples with the nominal composition of (La0.7Ca0.3MnO3)1–x /(LaMnO3)x with x = 0.00, 0.05, 0.15 and 0.25 were fabricated using traditional solid‐state reaction method. The electrical‐magnetic transport behavior and magnetoresistance (MR) were studied for the composites in magnetic fields H = 0.3 T, 3 T. Experimental results show that with the increasing of LaMnO3 (LMO) content x, the metal–insulator (M–I) transition temperature TP shifts to lower temperature and the resistivity increases sharply in zero magnetic field. Meanwhile, a significant enhancement in MR is observed for the composites, especially in the low temperature range (below TP). Specially, the maximum MR at 3 T increased from 35% for the pure La0.7Ca0.3MnO3 (LCMO) to 92% for the sample with x = 0.25. We suggest that such enhancement in MR is attributed to the strong ferro–antiferromagnetic coupling effects in the composite system, which increase the magnetic disorder at the grain surface and boundary, will improve the spin‐polarized tunneling process of the conducting electron between adjacent grains, and thus enhance the MR effect. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)