Structural, electrical and enhanced low field magneto-transport properties of La0.7Sr0.3MnO3 and (1-x) La0.7Ca0.2Sr0.1MnO3 (LCSMO) + (x) MgO composites

摘要

We report the effect of MgO phase on structural, electric and thermo electric properties of La0.8Sr0.2MnO3 (LSMO) and manganite matrix-based composite series (1-x) La0.7Ca0.2Sr0.1MnO3 + (x) MgO with x = 0.0, 0.05, 0.10, 0.15 (abbreviated as LCSMO - MgO) synthesized by solid-state reaction method. X-ray diffraction (XRD) data infers that manganite LSMO compound possesses a rhombohedrally-distorted structure (space group R3c), LCSMO has an orthorhombic structure (Pnma space group) while to that MgO compound crystallizes in cubic structure (space group Fd3m). XRD shows coexistence of MgO and La0.7Ca0.2Sr0.1MnO3 phases in doped composites through their characteristic peaks. The temperature dependence of resistivity shows that the transport behavior of the composites is governed by the grain boundaries. These composites shows metal-insulator transitions at T = T-MI which decreases with increasing MgO concentration. The magnetoresistance (MR) in this system increases with increasing MgO content, showing a maximum value (91% at 50 K and at lower fields) for (0.85) LCSMO - (0.15) MgO sample, which is larger than the largest MR value of pure La(0.7)ca(0.2) Sr0.1MnO3 (44% at 50 K). From thermoelectric power measurements, it is observed that electron-magnon scattering process is dominant mechanism in the low temperature region. (C) 2017 Elsevier B.V. All rights reserved.