过渡金属和镧系金属环状分子磁体的中子散射研究

The understanding of the magnetic structure and interactions is crucial in the study on 3d-4f molecular magnets. Due to the complexity of spin structure, magnetic exchange-coupling pathways, spin multiplets, and magnetic anisotropies, the correct determination of the magnetic structure and spin dynamics of molecular magnets remains challenging. In heterometallic {Cr8Ln8} and {Fe8Ln8} (Ln=Y,Dy) 3d-4f molecular magnets, the magnetic centers form wheel-like structures, providing valuable test beds for addressing quantum phenomena in finite-size spin systems. The element substitution plays a key role in tuning the magnetic properties of these 3d-4f molecular wheels. This project aims to perform an extensive investigation of the magnetic structure and interactions in {Cr8Ln8} and {Fe8Ln8} by means of advanced neutron scattering methods and physical property characterizations. The magnetic structure will be resolved by analyzing the short-range spin correlations, which can only be extracted by using diffuse neutron scattering with 3D polarization analysis. The magnetic excitations will be measured by means of inelastic neutron scattering and low-temperature specific heat with varying external magnetic fields. The low-lying energy spectra of the magnetic molecules and the interactions between magnetic moments will be determined accordingly. Through a systematic study on the 3d-4f molecular wheels family of {Cr8Ln8} and {Fe8Ln8}, we expect to achieve a sound knowledge of the effect of element substitution on the magnetic micro-structure and spin dynamics and the macro magnetic properties. The achievements of this project are of great importance to improve the design and synthesizing strategy of 3d-4f molecular magnets with fascinating magnetic properties. The experimental and theoretical methods employed in this research will improve the development and perfection of the neutron scattering application in molecular magnetism.

环状3d-4f异金属分子磁体因为其特殊的拓扑结构和磁学性质，成为研究零维磁学系统中经典与量子行为共存现象的绝佳平台。微观磁精细结构和磁相互作用是理解3d-4f分子磁体微观磁学机制与宏观磁学性能之间关系的关键。本课题采用极化中子及非弹性中子散射与常规物性测量相结合的研究方法，解决复杂分子磁体基态磁精细结构及磁相互作用的实验表征难题，揭示微观磁结构与自旋动力学对宏观磁性的影响机制。通过金属元素定向替代实现对磁学性能的精确调控，阐明磁性中心和配位体的选择与分子磁体磁学性质之间的关系，为3d-4f分子磁体的分子设计以及磁学性能的优化提供重要的实验依据。本课题对发展研究复杂分子磁性体系微观磁学机制的实验和理论分析方法具有重要意义。

3d-4f分子磁体具有独特的拓扑结构和磁学性质，有望实现高密度磁存储和量子计算等重要应用。3d-4f分子磁体的微观磁结构和自旋动力学是其宏观磁性的物理基础，弄清这些微观磁学机制对高性能分子磁体的设计与合成具有重要意义，但在这方面，直接的实验表征手段仍比较匮乏。本项目结合磁学、热学、以及极化和非弹性中子散射技术，对合成的四种环状3d-4f分子磁体（{Cr8Y8}、{Cr8Dy8}、{Fe8Y8}、{Fe8Dy8}）的磁结构和自旋动力学进行了深入的研究，全面认识了材料的磁学特性，揭示了它们的结构、宏观磁性、以及微观磁学机制之间的关联。项目的主要研究内容和相关成果包括：（1）测量了直流和交流磁化率，表征宏观磁学行为，确定化合物是否具有单分子磁体性质；（2）测量了低温比热，通过拟合确定低能磁激发；（3）进行了非弹性中子散射实验，结合比热结果，给出了分子的低能量磁能级谱，并得出磁性离子之间的磁相互作用；（4）进行了极化中子散射实验，通过理论计算判断磁性分子的基态磁结构；（5）进行了高频高场电子顺磁共振实验，确定了磁性分子的零场劈裂参数。这些研究成果对分子磁体的磁结构和自旋动力学的表征研究具有重要意义，深化了对分子磁体微观磁学机制和宏观磁性之间关系的理解。. 通过4年期的项目执行，项目组克服了新冠疫情的影响，顺利完成了项目任务。在本项目资助下，课题组已发表论文6篇，其中SCI论文5篇，EI论文1篇，另有多篇论文正在撰写。培养硕士研究生1名。