Jeddi M, Gharsallah H, Bekri M, Dhahri E, Hlil E K
Laboratoire de Physique Appliquée, Faculté des Sciences, Université de Sfax B. P. 1171 3000 Sfax Tunisia
Institut Préparatoire aux Études d'Ingénieur de Sfax, Université de Sfax B. P. 1172 3018 Sfax Tunisia.
RSC Adv. 2018 Aug 13;8(50):28649-28659. doi: 10.1039/c8ra05230a. eCollection 2018 Aug 7.
The present study involves an investigation of structural, magnetic and magnetocaloric effect (MCE) properties of 0.75LaCaMnO/0.25LaSrMnO composite material. Crystal structure analysis is performed by using Rietveld refinement of the X-ray diffraction patterns. The studied composite exhibits two structural phases; the rhombohedral and the orthorhombic structures corresponding to the mother compounds; LaCaMnO and LaSrMnO, respectively. The scanning electron microscopy micrographs support our findings. Magnetic measurements as a function of temperature of the composite display two successive second order magnetic phase transitions at 255 and 365 K associated to both mother compounds. Therefore, a broadening of the magnetic entropy change peak is noted. A better relative cooling power (RCP) value of 360 J kg compared to those observed in mother compounds is obtained at = 5 T, making of this material considered as a suitable candidate for magnetic refrigeration applications near room temperature. A consistent agreement between experimental results and numerical calculations based on the rule of mixtures has been shown. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems. The field dependence of the magnetic entropy change is applied to study the critical behavior. Our results go in tandem with the values corresponding to the mean field model. The spontaneous magnetization values determined using the magnetic entropy change (Δ ) are in good agreement with those found from the classical extrapolation of Arrott curves ( / ).
本研究涉及对0.75LaCaMnO/0.25LaSrMnO复合材料的结构、磁性和磁热效应（MCE）特性的研究。通过对X射线衍射图谱进行Rietveld精修来进行晶体结构分析。所研究的复合材料呈现出两个结构相；分别对应于母体化合物LaCaMnO和LaSrMnO的菱面体结构和正交结构。扫描电子显微镜显微照片支持了我们的发现。该复合材料的磁性测量结果显示，在255 K和365 K时存在两个连续的二级磁相变，这与两种母体化合物相关。因此，注意到磁熵变峰变宽。在磁场强度为5 T时，该材料获得了360 J kg的相对制冷功率（RCP）值，优于在母体化合物中观察到的值，这使得该材料被认为是室温附近磁制冷应用的合适候选材料。实验结果与基于混合法则的数值计算之间显示出一致的一致性。使用朗道理论对MCE进行的理论建模显示与实验数据有可接受的一致性，表明磁弹性耦合和电子相互作用在锰氧化物系统的MCE特性中具有重要性。磁熵变的磁场依赖性被用于研究临界行为。我们的结果与平均场模型对应的值一致。使用磁熵变（Δ ）确定的自发磁化值与从阿罗特曲线（ / ）的经典外推法得到的值非常一致。
