Hybridization Effects, Bonding Anisotropy and Magnetism in Uranium Intermetallics

****非技术摘要****已知许多铀化合物表现出不寻常的磁性，其原因在科学界仍有很大争议。这个项目试图揭示一些潜在的机制，这个研究者将利用中子衍射和高磁场研究的结合。中子衍射一直是在微观水平上测试材料结构和磁性能的首选技术，而在高磁场下的研究则测量宏观响应。该项目旨在为这类化合物的磁性和原子构型之间的相关性提供重要的见解。人们普遍认为，铀化合物的内聚性和磁性都受到铀原子电子与邻近原子电子相互作用的强烈影响。这个团体用术语“杂交”来形容它。为了描述这种相互作用，但它还没有被充分地纳入现有的理论。这个项目的结果旨在精确地指出这种机制。该项目将有助于材料科学项目的发展，这是一个快速发展的领域，有许多有益的职业机会。新密歇根州立大学的这个项目预计将提高新墨西哥州南部和德克萨斯州西部以西班牙裔为主的社区的科学能力。****技术摘要****毫无疑问，铀5f态与配体电子态之间的杂化效应对铀金属间化合物中磁矩和长程磁序的发展起着重要的作用。即便如此，到目前为止，还没有一个完全令人满意的理论模型来解释这些材料的磁性。本研究提出了一个系统的深入研究杂化在铀金属间化合物中磁序及其各向异性演化中的作用。将对具有不同化学计量的同结构铀化合物家族进行有力的研究。这些化合物的性质将通过化学取代和/或修改外部变量，如磁场或外部静水压力，调整到临界值。利用中子衍射和强磁场技术的结合，将确定单个化合物的结构和磁性参数。特别强调的是测试磁性和原子间距离之间的相关性，这被认为与不同杂化效应的强度密切相关。该研究将为学生提供实践训练，使他们成为中子散射和高磁场设施的合格使用者。

****NON-TECHNICAL ABSTRACT****Many uranium compounds are known to exhibit unusual magnetic properties, and the reason for that is still heavily disputed within the scientific community. This project attempts to shed some light onto the underlying mechanisms, and this investigator will utilize a combination of neutron-diffraction and high-magnetic-field studies. Neutron diffraction has been the technique of choice when it comes to testing structural and magnetic properties of a material at a microscopic level, and studies in high magnetic fields measure the macroscopic response. This project is intended to provide important insight into the correlations between magnetism and atomic configuration in such compounds. It is widely accepted that both the cohesive and the magnetic properties of uranium compounds are strongly influenced by interactions of electrons belonging to uranium atoms with the electrons of neighboring atoms. The community has phrased the term ?hybridization? in order to describe such interactions, but it has not been adequately included into existing theories. The results of this project are intended to pinpoint exactly that mechanism. This project will contribute to the development of a strong Materials Science program, a fast-growing field with many rewarding career opportunities. The program at NMSU is expected to increase scientific capacity in the predominantly hispanic communities in Southern New Mexico and Western Texas.****TECHNICAL ABSTRACT****There is little doubt that hybridization effects between the uranium 5f states and the electronic states of the ligands play a prominent role for the development of magnetic moments and long-range magnetic order in uranium intermetallics. Even so, to date, there is no fully satisfactory theoretical model of the magnetism in these materials. This single investigator proposes a systematic in-depth study of the role of hybridization for the evolution of magnetic order and its anisotropy in uranium intermetallics. A vigorous study on families of isostructural uranium compounds with different stoichiometries will be performed. The properties of these compounds will be tuned to critical values by chemical substitutions and/or modifying external variables, such as magnetic fields or external hydrostatic pressure. Using a combination of neutron-diffraction and high-magnetic-field techniques, the structural and magnetic parameters of the individual compounds will be determined. Particular emphasis is put onto testing the correlation between magnetism and interatomic distances, which is believed to be intimately related to the strength of different hybridization effects. The research will provide hands-on training for students to become qualified users at neutron-scattering and high-magnetic-field facilities.