钙钛矿型锰氧化物(La$lt;sub$gt;0.8$lt;/sub$gt;Eu$lt;sub$gt;0.2$lt;/sub$gt;)$lt;sub$gt;4/3$lt;/sub$gt;Sr$lt;sub$gt;5/3$lt;/sub$gt;Mn$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;7$lt;/sub$gt;的磁性和电性研究

采用传统固相反应法制备钙钛矿型锰氧化物 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇多晶样品, X-射线衍射分析表明, 样品(La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇结构呈现良好的单相. 通过磁化强度随温度的变化曲线(M-T)、不同温度下磁化强度随磁场的变化曲线(M-H)和电子自旋共振谱发现: 在300 K以下, 随着温度的降低, 样品先后经历了二维短程铁磁有序转变 (T_C^2D ≈ 282 K)、三维长程铁磁有序转变(T_C^3D ≈ 259 K)、奈尔转变(T_N ≈ 208K)和电荷有序转变(T_CO ≈ 35 K); 样品 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇在T_N以下, 主要处于反铁磁态; 在T_C^3D达到370 K时, 样品处于铁磁-顺磁共存态, 在370 K以上时样品进入顺磁态. 此外, 分析电阻率随温度的变化曲线(ρ-T)得到: 样品在金属-绝缘转变温度(T_P ≈ 80 K)附近出现最大磁电阻值, 其位置远离T_C^3D, 表现出非本征磁电阻现象, 其磁电阻值约为61%. 在T_CO以下, 电阻率出现明显增长, 这是由于温度下降使原本在高温部分巡游的e_g电子开始自发局域化增强所致. 通过对 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇的ρ-T 曲线拟合, 发现样品在高温部分的导电方式基本遵循小极化子的导电方式. 关键词： 磁性 电性 金属-绝缘转变温度 电子自旋共振

Magnetic and transport properties of bilayered perovskite manganites (La0.8Eu0.2)4/3Sr5/3Mn2O7

Samples of (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇ were prepared by solid state reaction method. X-ray diffraction patterns indicated that the sample shows no any asymmetry and no any trace of secondary phase. The magnetization curve as a function of temperature (M-T), the magnetization versus magnetic field (M-H) at different temperatures, and the electron spin resonance spectrum have been detected. The magnetization measurement reveals that with lowing temperature, all of the samples undergo a complex magnetic transition. They transform from the two-dimensional short-range ferromagnetic order at T_C^2D ≈ 282 K, and enter the three-dimensional long-range ferromagnetic state at T_C^3D ≈ 259 K. Then they step into the antiferromagnetic state at T_N ≈ 208 K and enter electric charge temperature order at T_CO ≈ 35 K. The antimagnetic phase is found in the sample (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇below T_N. When T_C^3D=370 K, the paramagnetic phase and antimagnetic phase co-exist. When T_C^3D is above 370 K, only paramagnetic phase exists in the sample. Besides, through electrical resistivity versus temperature curve ρ-T, the sample shows the maximum magnetization electrical resistivity when metal-insulator transition temperature is reached T_P ≈ 80 K, T_P being far from T_C^3D. And the transition shows the phenomenon of intrinsic magnetization electrical resistance, MR ≈ 61%. The resistance begins to increase below T_CO. Because of the lowing temperature, the itinerant electron e_g becomes increasingly spontaneously localized. One can see from the fitted ρ-T curves that (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇ in high temperature range is in accordance with the small polaron mode range hopping conduction.
Keywords： magnetic property electrical property metal-insulator transition electron spin resonance