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采用传统固相反应法制备钙钛矿锰氧化物La1.2-xTbxSr1.8Mn2O7(x=0.0,0.05)多晶样品,通过测量样品的磁化强度与温度关系曲线(M-T)和磁化强度与外加磁场关系曲线(M-H)对两样品的磁熵变研究发现:在整个温度测量区间内,x=0.0和x=0.05两样品在高温部分均表现出顺磁性;随着温度的降低,两样品分别在245 K和225 K处发生了二维短程铁磁有序转变(TC2D);在120 K和70 K处发生了三维长程铁磁有序转变(TC3D);在低温部分,两样品均表现出团簇自旋玻璃行为。x=0.0样品在TC3D附近的磁相变为一级相变,x=0.05样品为二级相变,两样品的磁熵变曲线的对称性良好,且在外场2 T下两样品在TC3D附近出现的最大磁熵变值分别为:2.17 J/(kg·K)和1.6 J/(kg·K),因此两样品有利于应用在埃里克森磁制冷循环中。此外,通过测量零场下电阻率与温度关系曲线(ρ-T)对两样品的电输运性质研究发现:x=0.0样品和x=0.05样品分别在96 K和93 K处发生了绝缘-金属转变(TP),对TP以上的ρ-T曲线拟合表明,两样品在高温部分均遵循三维变程跳跃的导电方式,Tb3+离子的掺杂没有改变高温区的导电方式。
The solid state reaction method was used to prepare polycrystalline La1.2-xTbxSr1.8Mn2O7 (x = 0.0,0.05) polycrystalline samples with perovskite. By measuring the relationship between magnetization and temperature (MT) and magnetization of samples, The results of magnetic entropy change of the two curves showed that the two samples exhibited paramagnetism at high temperature in the entire temperature measurement interval. As the temperature decreased, Two-dimensional short-range ferromagnetic order transition (TC2D) occurred at 245 K and 225 K, and three-dimensional long-range ferromagnetic order transition (TC3D) occurred at 120 K and 70 K. In the low temperature region, Cluster spin-glass behavior. The magnetic phase of the sample near TC3D changed into first-order phase transition when x = 0.0. The second-order phase transition was observed at x = 0.05. The symmetry of the magnetic entropy curves of the two samples was good, and the two samples near the TC3D The maximum values of magnetic entropy change are 2.17 J / (kg · K) and 1.6 J / (kg · K), respectively. Therefore, the two samples are suitable for the Erichsen magnetic refrigeration cycle. In addition, the electrical transport properties of the two samples were investigated by measuring the resistivity versus temperature (ρ-T) at zero field. The results show that the x = 0.0 and x = 0.05 samples were insulated at 96 K and 93 K, respectively. Metal transition (TP). The ρ-T curve fitting over TP shows that the two samples all follow the three-dimensional jump in the high-temperature part. The doping of Tb3 + ions did not change the conductivity of the high temperature part.