Anomalous transport effects for the metal and insulator doped La0.833K0.167MnO3 systems

Abstract The La0.833K0.167MnO3:Ag2O and the La0.833K0.167MnO3:SrTiO3 samples are fabricated by the sol–gel method. The microstructure, magnetic and transportation properties have been systematically studied. X-ray diffraction patterns show that the La0.833K0.167MnO3:Ag2O (abbreviated as LKMO/Ag) sample is a two-phase composite and consists of a magnetic La0.833K0.167MnO3 (abbreviated as LKMO) perovskite phase and a nonmagnetic Ag metal phase, while the structure of the La0.833K0.167MnO3:SrTiO3 (abbreviated as LKMO/STO) sample is a homogeneous solid solution phase. Comparing with the pure LKMO sample, the room temperature magnetoresistance (MR) effect for the LKMO/Ag sample is enhanced significantly due to the addition of Ag metal. The MR ratio increases from ∼25% for the pure LKMO sample to 65% for the LKMO/Ag sample under a higher field of 5.5 T at 300 K. For the LKMO/STO sample, however, the room temperature MR effect is weakened dramatically and is almost close to zero due to the addition of SrTiO3 insulator. In the low temperature regime below the Curie temperature, the MR behaviors are different from that of the room temperature; that is, the MR effect is decreased for the LKMO/Ag sample and increased for the LKMO/STO sample with temperature decrease. In fact, the low-field (μ0H=0.5 T) MR decreases from 32% to 5% for the LKMO/Ag sample, while increasing from 0.07% to 25% for the LKMO/STO sample with decreasing temperature from 300 to 4 K. The relative change between the intrinsic and the extrinsic MR, and varied roles of the spin-polarized-tunneling and the spin-dependent scattering mechanisms in different temperature regimes are employed to interpret the anomalous transport behaviors.