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首页> 外文期刊>RSC Advances >Magnetic entropy table-like shape and enhancement of refrigerant capacity in La1.4Ca1.6Mn2O7–La1.3Eu0.1Ca1.6Mn2O7 composite
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Magnetic entropy table-like shape and enhancement of refrigerant capacity in La1.4Ca1.6Mn2O7–La1.3Eu0.1Ca1.6Mn2O7 composite

机译：La1.4Ca1.6Mn2O7–La1.3Eu0.1Ca1.6Mn2O7复合材料的磁熵表形状和制冷能力的增强

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In this work, we have investigated the structural, magnetic and magnetocaloric properties of La _(1.4) Ca _(1.6) Mn _(2) O _(7) (A) and La _(1.3) Eu _(0.1) Ca _(1.6) Mn _(2) O _(7) (B) oxides. These compounds are synthesized by a solid-state reaction route and indexed with respect to Sr _(3) Ti _(2) O _(7) -type perovskite with the I 4/ mmm space group. The substitution of La by 10% Eu enhances the value of magnetization and reduces the Curie temperature ( T _(C) ). It is also shown that these compounds undergo a first-order ferromagnetic–paramagnetic phase transition around their respective T _(C) . The investigated samples show large magnetic entropy change (Δ S _(M) ) produced by the sharp change of magnetization at their Curie temperatures. An asymmetric broadening of the maximum of Δ S _(M) with increasing field is observed in both samples. This behaviour is due to the presence of metamagnetic transition. The Δ S _(M) ( T ) is calculated for A _( x ) /B _(1? x ) composites with 0 ≤ x ≤ 1. The optimum Δ S _(M) ( T ) of the composite with x = 0.48 approaches a nearly constant value showing a table-like behaviour under 5 T. To test these calculations experimentally, the composite with nominal composition A _(0.48) /B _(0.52) is prepared by mixing both individual samples A and B. Magnetic measurements show that the composite exhibits two successive magnetic transitions and possesses a large MCE characterized by two Δ S _(M) ( T ) peaks. A table-like magnetocaloric effect is observed and the result is found to be in good agreement with the calculations. The obtained Δ S _(M) ( T ) is ≈4.07 J kg ~(?1) K ~(?1) in a field change of 0–5 T in a wide temperature span over Δ T _(FWHM) ～ 68.17 K, resulting in a large refrigerant capacity value of ≈232.85 J kg ~(?1) . The MCE in the A _(0.48) /B _(0.52) has demonstrated that the use of composite increases the efficiency of magnetic cooling with μ _(0) H = 5 T by 23.16%. The large Δ T _(FWHM) and RC values together with the table-like (?Δ S _(M) ) ~(max) feature suggest that the A _(0.48) /B _(0.52) composite can meet the requirements of several magnetic cooling composites based on the Ericsson-cycle. In addition, we show that the magnetic field dependence of MCE enables a clear analysis of the order of phase transition. The exponent N presents a maximum of N > 2 for A, B and A _(0.48) /B _(0.52) samples confirming a first-order paramagnetic–ferromagnetic transition according to the quantitative criterion. The negative slope observed in the Arrott plots of the three compounds corroborates this criterion.
机译：在这项工作中，我们研究了La _（1.4）Ca _（1.6）Mn _（2）O _（7）（A）和La _（1.3）Eu _（0.1）Ca的结构，磁性和磁热性质_（1.6）Mn _（2）O _（7）（B）氧化物。这些化合物通过固态反应路线合成，并相对于具有I 4 / mmm空间基团的Sr_（3）Ti_（2）O_（7）型钙钛矿索引。用10％Eu代替La可以提高磁化强度并降低居里温度（T _（C））。还显示这些化合物在其各自的T_（C）附近经历一阶铁磁-顺磁相变。所研究的样品显示出在居里温度下由于磁化强度的急剧变化而产生的大的磁熵变化（ΔS _（M））。在两个样品中均观察到最大ΔS _（M）随电场增加而发生不对称扩宽。此行为是由于存在超磁跃迁。计算0≤x≤1的A _（x）/ B _（1？x）复合材料的ΔS _（M）（T）。x的复合材料的最佳ΔS _（M）（T） = 0.48接近一个几乎恒定的值，在5 T下表现出类似表格的行为。为了实验测试这些计算，通过混合两个单独的样品A和B制备标称成分为A _（0.48）/ B _（0.52）的复合材料。磁测量表明，该复合材料表现出两个连续的磁跃迁，并具有以两个ΔS _（M）（T）峰为特征的大MCE。观察到类似表的磁热效应，发现结果与计算结果非常吻合。在ΔT _（FWHM）〜68.17的宽温度范围内，在0-5 T的场变化下，获得的ΔS _（M）（T）约为4.07 J kg〜（？1）K〜（？1）。 K，导致较大的制冷剂容量值≈232.85J kg〜（？1）。 A _（0.48）/ B _（0.52）中的MCE已证明，使用复合材料可以使μ_（0）H = 5 T的磁冷却效率提高23.16％。较大的ΔT _（FWHM）和RC值以及表状（ΔΔS _（M））〜（max）特性表明A _（0.48）/ B _（0.52）复合材料可以满足要求基于爱立信循环的几种磁性冷却复合材料的制造。此外，我们证明了MCE的磁场依赖性可以清楚地分析相变的顺序。对于A，B和A _（0.48）/ B _（0.52）样本，指数N表示N> 2的最大值，从而证实了根据定量标准的一阶顺磁-铁磁跃迁。在三种化合物的Arrott图中观察到的负斜率证实了这一标准。

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