新型Al-TM-Nd(TM=Fe, Co, Ni)单相合金晶体结构与磁性关系研究

The ternary alloys of Al-TM-Nd (TM=Fe, Co, Ni) systems have attracted the attention of researchers because of their excellent magnetic properties. However, there are still a large number of new phases that have not been reported in these systems. Moreover, the study on the magnetic source of single-phase alloys in these ternary systems is far from being comprehensive and thorough, and the influence mechanism of chemical composition and crystal structure on the magnetic properties of the single-phase alloys has not been well explained. Furthermore, the first-principle calculation based on density functional theory is especially suitable for exploring the microscopic mechanism of magnetic properties of materials. Therefore, in this project, a series of novel single-phase alloys with the crystal systems of cubic, hexagonal, tetragonal and orthorhombic structure will be designed and prepared. The crystal structures of novel alloys will be studied by X-ray powder diffraction technique, Rietveld refinement and other methods, and the magnetic properties of novel alloys will be measured and analyzed. The electronic state density, crystal structure and magnetic properties will be calculated and discussed by LDA+U functional method based on the density functional theory of first-principle. From both macro (magnetic presentation, etc.) and micro (atomic arrangement, electron orbit, etc.) perspectives, the magnetic source of the single-phase alloys will be analyzed, the effect of each element in the single-phase alloys on the magnetic properties will be discussed, and the influence law and mechanism of chemical composition and crystal structure on their magnetism will be revealed. This project will provide theoretical and experimental basis for the alloy preparation, analysis, identification, structural research, magnetic design, performance mining and material development of the related materials.

Al-TM-Nd（TM=Fe, Co, Ni）体系三元合金因具有良好的磁性能而受到研究者的关注。但是，该体系合金尚有大量新型物相未见报道，对其磁性来源，元素成分、晶体结构对磁性能的影响机理等还没有得到较好的解释，而基于密度泛函理论的第一性原理尤其适用于探索材料磁性的微观机制。因此，本项目拟通过设计、制备系列立方、六方、四方、正交等晶系新型单相三元合金。利用X-射线粉末衍射技术及Rietveld精修等方法，研究该体系新型合金的晶体结构，测试分析其磁性能。结合第一性原理基于密度泛函理论的LDA+U方法对其电子态密度、晶体结构与磁性能的计算结果进行讨论，从宏观磁性表现和微观原子排列、电子轨道等两个层面分析单相合金的磁性来源，探讨合金各组成元素对磁性的贡献，揭示化学成分、晶体结构对其磁性的影响规律和机理。为相关材料的合金制备、分析鉴定、结构研究、磁性设计、性能挖掘、材料开发提供理论和实验依据。

Al-TM-Nd (TM=Fe, Co, Ni)体系三元合金因具有潜在的优异磁性能而备受关注。项目针对该体系合金物相数量报道不足、化学组成及晶体结构对合金磁性变化的影响不清、合金磁性来源等问题展开研究。通过设计、配料、熔炼、均匀化退火处理成功制备Al3FeNd2、Al3CoNd2、Al2Fe3Nd、Al1.5Co3.5Nd、Al1.5Ni3.5Nd、Al2Ni3Nd、Al2.5Ni2.5Nd、Al15Fe9Nd2、Al10Fe2Nd、Al5Ni2Nd等该体系十种未曾报道过的三元单相合金；利用X-射线粉末衍射技术、Rietveld结构精修方法分析上述十种新型三元单相合金的晶体结构。分别测试分析立方Al3FeNd2、Al3CoNd2，六方Al2Fe3Nd、Al1.5Co3.5Nd、Al1.5Ni3.5Nd、Al2Ni3Nd、Al2.5Ni2.5Nd，四方Al15Fe9Nd2，正交Al10Fe2Nd、Al5Ni2Nd等该体系新型三元单相合金的磁性能。此外，分别对立方Al3FeNd2和Al3FeGd2、立方Al3TRNd2 (TR=Fe, Co, Cu)、六方Al2Fe3Nd和Al2Ni3Nd、六方Al1.5Co3.5Nd和Al1.5Ni3.5Nd、六方AlxNi5-xNd (x=1, 1.5, 2, 2.5)、六方Al2Ni3Nd和Al2Ni3Tb、四方Al15+xFe9-xNd2 (x=0, 1)、四方Al15Fe9RE2 (RE=Nd, Gd, Tb)、四方Al8Fe4Nd和Al8Cu2Fe2Nd、正交Al10Fe2Nd和Al10Fe2Er等系列合金的磁性进行对比研究，探讨磁性能随化学成分、晶体结构变化的规律。最后，采用基于密度泛函理论的第一性原理方法计算单相合金的晶体结构及磁性能，解释合金磁性的成分及电子轨道来源。Al3FeNd2和Al2NdNi3晶胞通过几何优化，其晶格常数与实验值相吻合。Al3FeNd2是一种自发磁矩为4.11 μB/f.u.的亚铁磁体，自发磁矩源于Fe(16c)-3d和Nd(8b)-4f轨道电子的自旋；而Al2NdNi3是一种自发磁矩为0.28 μB/f.u.的铁磁体，自发磁化源于Nd(1a)-4f能带中电子的自旋。模拟计算值与实验值是一致的。研究结果为相关材料的合金制备、分析鉴定、结构研究、磁性设计、性能挖掘、材料开发提供实验和理论依据。