Effects of Ag Doping on Magnetoresistance of La_0.833K_0.167MnO₃ Polycrystalline Perovskite Manganites

The microstructure, magnetic and transport properties of the heterogeneous system with a nominal composition (1/m)Ag₂O-La_0.833K_0.167MnO₃ (1/m is molar ratio with m = 32, 16, 8, 4, and 2) have been studied. The x-ray diffraction patterns show that all the samples are the two-phase composite and consist of a magnetic La_0.833K_0.167MnO₃ (LKMO) perovskite phase and a nonmagnetic metal Ag phase. The room-temperature magnetoresistance (MR) effect is enhanced significantly due to the addition of Ag. For the m = 4 sample, we obtain the MR values up to 32% under a lower field of 0.5 T and 67% under a higher field of 5.5 T at the temperature of 300 K, which are much larger than the corresponding MR values (10% and 35%) of the LKMO sample without Ag. In the low temperature range from 4.2 K to 250 K, the MR values of the Ag-added samples however decrease with the increasing Ag content in the samples. The effect is discussed qualitatively by using the relative contribution from the intrinsic MR effect and the extrinsic MR effect including the spin-polarized-tunneling and spin-dependent scattering effects in different temperature regions.