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首页> 外文期刊>Journal of Experimental and Theoretical Physics >Investigation of Magnetic Phase Transformations in a System of Nd_(1-x)Ba_xMnO_(3-δ)(0 ≤ x ≤ 0.50) Depending on the Conditions of Preparation
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Investigation of Magnetic Phase Transformations in a System of Nd_(1-x)Ba_xMnO_(3-δ)(0 ≤ x ≤ 0.50) Depending on the Conditions of Preparation

机译：Nd_（1-x）Ba_xMnO_（3-δ）（0≤x≤0.50）系统中磁相变的研究取决于制备条件

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摘要

Investigations are performed of the crystal structure and magnetic and electromagnetic properties of single crystals (0.23 ≤ x ≤ 0.34) and polycrystals (0 ≤ x ≤ 0.50) of an Nd_(10x)Ba_xMnO_(3-δ) system of solid solutions. It is found that, for samples prepared in the air, the maximal Curie temperature (T_C) does not exceed 150 K, while, in the case of polycrystalline samples in the concentration range of 0.34 ≤ x ≤ 0.50, prepared in a reducing medium (a gaseous mixture of argon and carbon monoxide), T_C increases to 320 K. As a result of the reducing medium effect on the compositions, the type of the magnetic phase transition to the paramagnetic state changes from the first to second order. The electrical resistivity of reduced polycrystalline samples (0.34 ≤ x 0.50) decreases in magnitude and correlates with the behavior of magnetization. Both series of samples, prepared both in the air and in a reducing medium, exhibit a transition from the metal to dielectric state at a temperature below T_C. The temperature and field dependences of magnetization for the stoichiometric polycrystalline composition of Nd_(0.50)Ba_(0.50)MnO_3 are measured under conditions of hydrostatic pressure. It is demonstrated that the hydrostatic pressure induces in Nd_(0.50)Ba_(0.50)MnO_3 the transition from the antiferromagnetic to ferromagnetic state. Based on the measurement results, hypothetical magnetic phase diagrams are constructed for the system of solid solutions being treated, depending on the concentration of barium and the method of preparation. It is found that no T_C increase is observed in single crystals (0.23 ≤ x ≤ 0.34) such as is observed in polycrystals. It is assumed that the abrupt increase in T_C of polycrystallie samples prepared in a reducing medium is a result of the emergence of extended defects and microstresses in the crystal lattice.
机译：研究了固溶Nd_（10x）Ba_xMnO_（3-δ）系统的单晶（0.23≤x≤0.34）和多晶（0≤x≤0.50）的晶体结构以及磁和电磁性能。发现对于空气中制备的样品，最高居里温度（T_C）不超过150 K，而对于浓度范围为0.34≤x≤0.50的多晶样品，则在还原介质中制备（ （氩气和一氧化碳的气态混合物），T_C增加到320K。由于介质对组合物的还原作用降低，磁相转变为顺磁态的类型从第一阶变为第二阶。还原的多晶样品（0.34≤x 0.50）的电阻率的幅度减小，并且与磁化行为相关。在空气和还原性介质中制备的两个系列的样品在低于T_C的温度下均表现出从金属到介电态的转变。在静水压的条件下，测量了化学计量的Nd_（0.50）Ba_（0.50）MnO_3的化学计量多晶组合物的磁化强度与温度的关系。结果表明，静水压力在Nd_（0.50）Ba_（0.50）MnO_3中引起从反铁磁状态到铁磁状态的转变。根据测量结果，根据钡的浓度和制备方法，为要处理的固溶体系统构建假设的磁相图。发现在单晶（0.23≤x≤0.34）中没有观察到T_C增加，在多晶体中没有观察到。假定在还原介质中制备的多晶样品的T_C突然增加是晶格中出现扩展缺陷和微应力的结果。

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