Giant magnetoresistance of the La1-xAgxMnO3 polycrystalline inhomogeneous granular system

A series of bulk polycrystalline La1-xAgxMnO3 samples with x ranging nomina lly from 0 to 0.5 were prepared by conventional solid-state reaction proces sing in air. X-ray diffraction patterns show that the samples contain a sin gle perovskite phase when x less than or equal to 0.25, and are composed of two phases (a magnetic perovskite phase and a nonmagnetic Ag-rich phase) f or x > 0.25. It is found that, in this series of polycrystalline samples, m aximum magnetoresistance occurs for x = 0.30, i.e., for a composite of the two phases whose magnetoresistance ratio is about 25.5% at room temperature . The enhancement of the magnetoresistance effect in such an inhomogeneous granular system can be attributed to the spin-dependent scattering of elect rons at the interface of the two phases. (C) 2000 American Institute of Phy sics. [S0003-6951(00)03731-1].