Magnetic and magnetocaloric properties of the Co2-xMn B system by experiment and density functional theory
Magnetic and magnetocaloric properties of the Co2-xMn B system by experiment and density functional theory
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DOI：
10.1016/j.actamat.2018.11.034
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发表时间：
2019-02
期刊：
影响因子：
9.4
通讯作者：
S. Ener;M. Fries;F. Hammerath;I. Opahle;E. Simon;P. Fritsch;S. Wurmehl;Hongbin Zhang;O. Gutflei
中科院分区：
文献类型：
--
作者：
S. Ener;M. Fries;F. Hammerath;I. Opahle;E. Simon;P. Fritsch;S. Wurmehl;Hongbin Zhang;O. Gutflei
Co 2 B系统在其居里温度附近显示出显著的磁体积效应，这使得其对于磁热应用或热磁发电具有潜在的吸引力，因为预期晶格和自旋自由度之间存在大的耦合。本文报道了一系列Co2-xMnx B合金的合成及其性能研究。结构分析表明，单相行为高达x= 0.8，在整个系列中没有结构对称性变化。宏观和局部磁性能的测量，揭示了一个异常的行为的自发磁化，居里温度，和元素特定的磁矩作为锰浓度的函数。使用核磁共振（NMR）的研究分析元素的贡献磁化。密度泛函理论（DFT）计算指导我们理解所观察到的异常的起源，这是由于Mn原子之间复杂的磁耦合行为，这显著影响了相应的交换相互作用。Co2-B合金的磁热性能表明，随着Mn含量的变化，最大熵变峰温度在室温和450 K之间移动，但对磁热响应没有明显影响.当x= 0.1，场变化为2 T时，在442 K时得到的熵变最大，为-1.37 J k g-1 K-1。然而，对于任何可能的磁热或热磁发电应用，该值都相当低。尽管如此，先进的表征和理论之间的良好的一致性提供了一个更深入的理解的Co 2-x Mn x B材料系统，在未来可以扩展到其他系统。
The Co 2 B system shows a significant magnetovolume effect around its Curie temperature which makes it potentially attractive for magnetocaloric applications or thermomagnetic power generation, as a large coupling between the lattice and spin degrees of freedom is expected. We report on the synthesis of a series of Co 2-x Mn x B alloys and the investigation of their properties. The structural analysis indicates a single phase behavior up to x= 0.8 with no structural symmetry changes throughout the series. Measurements of both, macroscopic and local magnetic properties, reveal an anomalous behavior of the spontaneous magnetization, Curie temperature, and element-specific magnetic moments as a function of manganese concentration. The elemental contributions to the magnetization are analyzed using nuclear magnetic resonance (NMR) studies. Density functional theory (DFT) calculations guide us in the understanding of the origin of the observed anomaly, which is due to a complex magnetic coupling behavior between Mn atoms, which significantly affects the corresponding exchange interactions. The magnetocaloric properties of the Co 2-x Mn x B alloys show that the maximum entropy change peak temperature can be shifted between room temperature and 450 K upon variation of the manganese concentration without significant impact on the magnetocaloric response. The highest entropy change of− 1.37 J k g− 1 K− 1 at 442 K is obtained for x= 0.1 for a field change of 2 T. This value is, however, quite low for any possible magnetocaloric or thermomagnetic power generation applications. Nevertheless, the good agreement between the advanced characterization and theory gives a deeper understanding of the Co 2-x Mn x B material system which can in the future be extended to other systems.