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首页> 美国卫生研究院文献>Journal of Applied Physics >Influence of Ca-deficiency on the magneto-transport properties in La0.8Ca0.2MnO3 perovskite and estimation of magnetic entropy change
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Influence of Ca-deficiency on the magneto-transport properties in La0.8Ca0.2MnO3 perovskite and estimation of magnetic entropy change

机译：钙缺乏对La0.8Ca0.2MnO3钙钛矿中磁输运性质的影响和磁熵变的估计

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摘要

La0.8Ca0.2 − x□xMnO3 (x = 0.00, 0.10, and 0.20) perovskite was prepared by the conventional solid-state reaction and annealed at 1473 K. X-ray diffraction and scanning electron microscopy shown the existence of a secondary phase attributed to the unreacted Mn3O4 oxide. The magneto transport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements under several applied magnetic fields. We note that the La0.8Ca0.2MnO3 (x = 0.00) sample has a classical metal-insulator transition at Tρ. But we have observed that the lacunars samples (x = 0.10 and 0.20) include a metallic and insulator behavior simultaneously below Tρ and the resistivity is dominated by tunneling through the barriers associated with the insulating phase. In other words, the calcium deficiency favors the enhancement of the insulator behavior. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Furthermore, we found that the estimated results are in good agreement with experimental data. Above all, the resistivity dependence on the temperature and magnetic field data is used to deduce the magnetic entropy change. We have found that these magnetic entropy change values are similar to those calculated in our previous work from the magnetic measurements. Finally, we have found an excellent estimation of the magnetic entropy change based on the Landau theory.
机译：通过传统的固相反应制备钙钛矿型La0.8Ca0.2·-x□xMnO3（x == 0.00、0.10和0.20），并在1473 K下进行退火.X射线衍射和扫描电子显微镜显示存在第二相归因于未反应的Mn3O4氧化物。基于在几个外加磁场下电阻率ρ（T）测量值的温度依赖性，研究了磁传输特性。我们注意到La0.8Ca0.2MnO3（x == 0.00）样品在Tρ处具有经典的金属-绝缘体跃迁。但是我们已经观察到，层状样品（x = 0.10和0.20）在Tρ以下同时具有金属和绝缘体行为，并且电阻率主要是通过隧穿与绝缘相相关的势垒来控制的。换句话说，钙缺乏有利于绝缘子性能的增强。电阻率符合现象渗透模型，该模型基于铁磁金属团簇和顺磁绝缘区的相分离。此外，我们发现估计结果与实验数据非常吻合。最重要的是，电阻率对温度和磁场数据的依赖性可用来推导磁熵变。我们已经发现，这些磁熵变值类似于我们先前的工作中从磁测量得出的值。最后，我们发现了基于Landau理论的磁熵变的极好估计。

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