强磁各向异性体系弛豫机理的研究

The discovery of single-molecule magnet (SMM) behavior, where relaxation and quantum tunneling of the magnetization result from a molecular-based blocking anisotropy, is recognized as an important breakthrough in the field of molecular-based magnetism, with the promise of a revolution in data storage and processing. Although the spin can be successfully maximized by generating ferromagnetically-coupled systems, the simultaneous control of the easy-axis anisotropy represents a major challenge. The objective of the present proposal is to produce and characterize new molecules based on highly anisotropic lanthanide ions with the goal of identifying features of relevance to modulating relaxation dynamics of SMMs. This task is far from straightforward and finding the relation between the chemical environment of metal centers and the magnetic anisotropy of the compound/fragment is fraught with difficulties. As a way to address this challenge, the synthetic strategy is to design new molecules where the anisotropic centers are in fine-tuned local environments by considering the metal topology, the ligands involved and the structural parameters of the molecule. Due to the complexity of such systems, it is almost impossible using routine experimental measurements to determine the microscopic nature of the states that control the magnetic relaxation. In this respect, a combination of experimental efforts (including INS) with high level fragment ab initio calculations is applied in order to extract information needed to elucidate the underlying relaxation dynamics. The information extracted from such studies will improve our understanding of the magnetic behaviour of SMMs and facilitate potential applications in data storage and processing, essential for the rational design of new molecular-based materials.

单分子磁体的发现是分子磁性材料研究近二十年来最重要的突破之一。近年来，人们在高基态自旋分子的设计上取得了显著进展，然而如何同时调控单轴磁各向异性依然是科学家们面临的一项挑战性课题。针对单分子磁体弛豫机理这一关键问题，本项目选择强各向异性稀土镝离子为自旋载体，考虑各种结构因素，设计结构新颖的磁性分子，系统研究金属离子的化学环境和金属离子间Ising磁交换/偶极相互作用对自旋-晶格弛豫的影响。通过详尽的磁性表征并结合先进的实验方法（如非弹性中子散射）和ab initio理论计算，揭示自旋载体的化学环境与磁各向异性之间的关系和稀土单分子磁体复杂弛豫过程的机理，阐明调控单分子磁体弛豫过程的机制。为实现稀土单分子磁体在信息存储和量子计算方面的应用提供重要科学数据。

通过调整稀土离子的配位构型及其之间的相互作用来调控单分子磁体性质是当前分子磁性研究的热点。本项目紧扣自旋载体的化学环境与化合物/断片单轴磁各向异性的相关性这一关键科学问题，重点研究了单分子磁体的弛豫调控机制。连接两个[DyZn]构筑单元可增强Dy离子各向异性和相互作用，获得性质优异的单分子磁体；通过结构-性质关系的深入探讨，发现呼啦圈形配位构型对于保持金属离子的强轴向进而实现单分子磁体效应具有重要作用；发现酰腙类配体的酮-烯醇互变异构影响配体场强度，造成金属离子各向异性的变化，从而影响化合物的弛豫行为；从结构及配体设计的角度全面总结了稀土单分子磁体的研究进展，阐述了稀土单分子磁体设计的整体思路。以上研究成果为我们进一步开展相关工作打下了良好的基础。