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

Highlights: ► Polycrystalline composites between La0.7Sr0.3MnO3 (LSMO) and La2O3 phases. ► The maximum LFMR value of 2.22% at 300 K in 500 Oe from the composite sample with 10 mol% La2O3 addition. ► Low resistivity level (<1 Ω cm) far below the metallic percolation threshold. ► Closely related with a characteristic microstructure variation of composite samples. ► High grain boundary areal density and sharpening of a disordered LSMO grain boundary region acting as more effective spin-dependent scattering centers. - Abstract: 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–xLa2O3 (x = 0, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3) were systematically investigated. Compared with pure LSMO (TC = 362 K), all composites exhibited a slightly depressed TC 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.