Effects of Ag Doping on Magnetoresistance of La0.833 K0.167MnO3 Polycrystalline Perovskite Manganites
The microstructure, magnetic and transport properties of the heterogeneous system with a nominal composition (1/m)Ag2O-La0.833K0.167MnO3 (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 two-phase composite and consist of a magnetic La0.833K0.167MnO3 (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 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. This effect is discussed qualitatively by using the relative contribution from the intrinsic MR effect and the extrinsic MR effect including the spin-polarized-tunnelling and spin-dependent scattering effects in different temperature regions.