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采用传统固相反应法制备钙钛矿型锰氧化物(La0.8Eu0.2)4/3Sr5/3Mn2O7多晶样品,X-射线衍射分析表明,样品(La0.8Eu0.2)4/3Sr5/3Mn2O7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(T2D C≈282K)、三维长程铁磁有序转变(T3D C≈259K)、奈尔转变(T N≈208K)和电荷有序转变(T CO≈35K);样品(La0.8Eu0.2)4/3Sr5/3Mn2O7在T N以下,主要处于反铁磁态;在T3D C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≈80K)附近出现最大磁电阻值,其位置远离T3D C,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(La0.8Eu0.2)4/3Sr5/3Mn2O7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.
The perovskite-type manganese oxide (La0.8Eu0.2) 4 / 3Sr5 / 3Mn2O7 polycrystalline samples were prepared by the conventional solid-state reaction method. X-ray diffraction analysis showed that the samples (La0.8Eu0.2) 4 / 3Sr5 / 3Mn2O7 The structure shows a good single phase.According to the curves of magnetization with temperature (MT), the curves of magnetization at different temperatures with magnetic field (MH) and electron spin resonance (NMR) spectroscopy found that under 300 K, with the decrease of temperature (T2D C≈282K), three-dimensional long-range ferromagnetic order transition (T3D C≈259K), Nel transition (TN≈208K) and charge-order transition (T CO ≈35K). The sample (La0.8Eu0.2) 4 / 3Sr5 / 3Mn2O7 is mainly in the antiferromagnetic state below TN. When the T3D C reaches 370 K, the sample is in the ferromagnetism-paramagnetic coexistence state and is above 370 K When the sample is in the paramagnetic state, the resistivity changes with the temperature (ρ-T): the maximum magnetoresistance value appears near the metal-to-insulator transition temperature (TP≈80K) The phenomenon of non-intrinsic magnetoresistance, the magnetic resistance of about 61%. Below the T CO, resistivity increased significantly, which is due to the temperature dropped to the original part in the high temperature The eg electron of the touring began to spontaneously localized and enhanced.According to the ρ-T curve fitting of (La0.8Eu0.2) 4 / 3Sr5 / 3Mn2O7, it was found that the conduction mode of the sample at high temperature basically followed the pattern of small polaron Conductive way.