Enhanced low field magnetoresistance in La0.7Sr0.3MnO3-La2O3 composites

A significant enhancement of low-field magnetoresistance (LFMR) was obtainable from the polycrystalline composites between La0.7Sr0.3MnO3 (LSMO) and La2O3 phases. For this study, the magnetic and magnetotransport properties of samples with various compositions of (1-x) LSMO-xLa(2)O(3) (x = 0, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3) were systematically investigated. Compared with pure LSMO (T-C = 362 K), all composites exhibited a slightly depressed T-C values of 355-358 K, implying that the magnetic ordering of LSMO is insignificantly affected by chemically compatible La2O3. While the LFMR value at 300 K in 500 Oe was monotonously increased from 1.36 to 1.67% with increasing x from 0 to 0.075, it was abruptly increased to the maximum value of 2.22% for x = 0.1 with only one order increase in its resistivity relative to x = 0.075, and further increasing x from 0.1 to 0.3 resulted in a linear decrease to 1.8% with almost no variation in resistivity. This peculiar behavior, different from normal metallic percolation threshold effect, is closely related to the microstructure variation. Remarkably improved LFMR properties of the LSMO-La2O3 composite samples are attributed to high grain boundary areal density and sharpening of a disordered LSMO grain boundary region acting as more effective spin-dependent scattering centers. (C) 2011 Elsevier B.V. All rights reserved.