Colossal magnetoresistance of bulk Ag-doped Nd0.7Sr0.3MnO3 two-phase composites

We have prepared a series of bulk polycrystalline manganites with the nominal compositions, Nd0.7Sr0.3MnO3-Agx (x is the molar fraction) with x = 0.1, 0.2, 0.3, 0.4, 0.5 by conventional solid-state reaction. The X-ray diffraction patterns show that the sample Nd0.7Sr0.3MnO3 (x = 0) is a single-phase compound with the pseudocubic perovskite structure, while the Ag-doped samples are two-phase composites consisting of a ferromagnetic perovskite phase and a nonmagnetic Ag metal phase. For all the samples, the Curie temperature, TC, remains nearly the same (228 ± 2 K), but the maximum magnetoresistance in a magnetic field of 1 T at 222 K is enhanced strongly due to the addition of Ag, namely, from 45% for the Nd0.7Sr0.3MnO3 sample to 188, 277, 142, 158 and 151% for the Nd0.7Sr0.3MnO3-Agx samples with x = 0.1, 0.2, 0.3, 0.4, and 0.5, respectively. This magnetoresistance-enhancement phenomenon can be attributed to the spin-dependent scattering of the spin-polarized electrons at the interfaces between the perovskite grains and the Ag granules.