SrTiO3掺杂La-K-Mn-O系统的电磁性质

用溶胶-凝胶制备了La_0.833K_0.167MnO₃-SrTiO₃ (LKMO/STO)系列样品，并研究了它们的结构、磁性和输运特性.X射线衍射实验表明，1200℃烧结的LKMO/STO (STLK12)是一个均匀的固溶相.其电阻率表现为绝缘体的行为，而纯La_0.833K_0.167MnO₃ (LKMO)样品随温度的升高则有金属-绝缘体转变.在低场下(μ₀H=0.02 T)，对STLK12样品，当温度从220 K降低到4 K时，磁电阻从0.2%升高到11%.在高场下(μ₀H=5.5 T)，随着温度降低，磁电阻几乎是线性增大.在4.2 K时，达到65%.比纯LKMO样品40%的磁电阻高出了25%. 我们用晶界处的自旋极化隧穿效应定性地解释了这种增强的磁电阻效应.关键词：低场磁电阻高场磁电阻自旋极化隧穿钙钛矿

Magnetic and electronic transport properties of SrTiO3-doped La-K-Mn-O system

La_0.833K_0.167MnO₃ (LKMO) and La_0.833K_0.167MnO₃/SrTiO₃ (LKMO/STO) are fabricated at different temperatures. STLK08, STLK10 and STLK12 stand for the samples sintered at 800, 1000 and 1200℃ respectively. X-ray diffraction (XRD) shows that all of the three samples consisted of homogeneous solid solution phases. The resistivity for LKMO shows insulator-metal transition with decreasing temperature, but the resistivities of STLK10 and STLK12 show an insulator behavior over the whole temperature regime (4—300 K). The low-field (0.02 T) magnetoresistance increases from 0.2% to 11% with temperature decreases from 250 K to 4 K for STLK12 sample. The high field (μ₀H=5.5 T) magnetoresistance almost increases linearly with decreasing temperature, which is much higher than the magnetoresistance of LKMO (The high field magnetoresistance are 65% and 40% at 4 K for STLK12 and LKMO, respectively). The enhancement in magnetoresistance is quantitatively explained by spin-polarized-tunneling at grain boundaries.