Effect of Ag substitution on the transport property and magneto resistance of LaMnO3

The structural, magnetic and electronic properties of the polycrystalline La1-xAgxMnO3 are systematically investigated as a function of Ag-doping level. The result of the Rietveld refinement of X-ray powder diffraction shows that the samples are single rhombohedral (R (3) over barC) structure phase for x<0.2. For xgreater than or equal to0.2, the samples are composed of a R (3) over barC perovskite phase and a nonmagnetic metal Ag phase. The temperature dependence of resistivity shows that all samples undergo a sharp insulator-metal (I-M) transition accompanying a paramagnetic to ferromagnetic transition with the decrease of temperature. However, for x<0.2, an obvious double I-M transition with a single ferromagnetic transition is observed. In the meanwhile, a large magnetoresistance (MR) with low applied magnetic field is observed. The electronic and magnetic inhomogeneity induced by Ag doping and the nonmagnetic metal Ag phase are presented to account for the transport properties and large MR in these compounds. (C) 2002 Elsevier Science B.V. All rights reserved.