Ag掺杂La_K_Mn_O非均匀多晶体系的电磁性质

The magnetic and electronic transport properties in Ag-doped La-K-Mn-O inhomogeneous system

用溶胶_凝胶方法制备了1/mAg2O_La0.833K0.167MnO3(LKMO/Ag)系列样品,其中1/m代表Ag2O和La0.833K0.167MnO3(LKMO)的摩尔比,m=32,16,8,4和2.研究了此系列样品的结构、磁性和输运特性.X射线衍射实验表明,LKMO/Ag是一个非均匀的系统,样品由磁性的钙钛矿相LKMO和金属Ag相组成.由于Ag相的加入,在室温条件下,磁电阻效应明显增强.在300K,0.5T磁场下,m=4样品的磁电阻可以达到32%;5.5T磁场下,其磁电阻可达64%.而单纯的LKMO样品在相同条件下的磁电阻分别为10%和35%.在低温下,加Ag样品的磁电阻效应反而减小,样品含Ag越多,磁电阻效应越小.用非本征磁电阻(包括自旋极化隧穿和自旋相关散射)和本征磁电阻在不同温区对总磁电阻的相对贡献对此系列样品的磁电阻现象作了定性的解释.

Microstructure, magnetic and electronic transport properties of the inhomogeneous system 1/m Ag20-La0.833Ko.167MnO3 （1/m is molar ratio, m = 32, 16, 8, 4, and 2） have been studied. X-ray diffraction patterns show that all the samples are the 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 the MR ratio increases from 10% of the pure compound LKMO to 32% under a lower field of 0.5 T and from - 35% of LKMO to 64 % under a higher field of 5.5 T at the temperature of 300 K. In the low temperature range from 4.2 K to 265 K, however, the MR ratio of the Ag-doped sample decreases with increasing the Ag content in the samples. The effect is discussed qualitatively by use of the relative change among the intrinsic MR effect and the extrinsic MR effect including the spin-polarizedtunneling and spin-dependent scattering effects at grain boundaries.