Understanding Spin-Spin and Spin-Lattice Interactions in Molecular Nanomagnetism

摘要：这个高度跨学科的项目涉及磁性分子的研究，磁性分子的性质可以在分子水平上进行化学工程，以获得所需的物理性质。这些所谓的分子纳米磁体为纳米尺度上的磁性提供了非凡的基础见解，同时有望在信息技术方面取得重要进展。在这方面，正在研究两个不同的重点：第一个涉及磁性分子作为经典计算机中的基本存储单元（位）的潜在用途，其中信息存储在分子的磁极化状态（上或下）；第二篇论文探讨了利用这些分子的量子态来实现量子计算算法的可能性。该项目采用了由美国国家高磁场实验室PI开发的独特的磁共振光谱技术，以建立结构-性质关系，化学家可以使用该技术为目标应用优化设计分子。尽管经典存储器和量子存储器（量子位）的设计标准有些不同，但在基本层面上，它们通常涉及调整/优化分子系统中相同的相互作用。研究小组正在探索磁性元素、分子几何形状和周围宿主材料的选择如何影响编码到磁性分子中的经典和量子信息的稳定性。该团队还在研究使用有机连接剂将磁性分子“连接”在一起的可能性。从项目中获得的结果对其他研究团体感兴趣，包括材料科学，无机和生物无机化学。PI坚定地致力于多样性，无论是在招生方面，还是通过积极参与美国物理学会的硕士到博士的桥梁计划和国家指导社区。技术摘要：分子纳米磁场在过去几年中取得了显著的进展，例如：磁性分子保持其磁化的温度提高了四倍；并且在分子装置中证明了对单个Tb核自旋的相干操纵和读出。对这两个结果至关重要的是对由具有强自旋轨道各向异性的磁性离子组成的简单分子的关注。最近的研究活动出现了两个截然不同的分支：第一个继续关注可以作为经典记忆元件的单分子磁铁（SMMs）；第二个推动力涉及分子纳米磁铁在量子计算应用中的潜在用途。该项目涉及这两个领域。smm的工作重点是：(i)涉及轨道简并过渡金属与一个或两个额外高自旋中心耦合的各向异性自旋轨道介导交换；（ii）各向异性镧系元素之间使用自旋支承（自由基）配体直接交换。这两种情况的目标都是获得简单但高度各向异性的分子（二聚体和三聚体），它们具有足够大的自旋基态，可以关闭防止磁化阻塞的量子隧道和自旋晶格弛豫途径。同时，（iii）自旋量子比特的研究主要集中在各向异性的单核物质上，在这些物质中，可以设计出防止偶极自旋自旋退相干的晶体场态。在这种情况下，自旋晶格弛豫最终会限制相记忆时间。高场/频率电子顺磁共振（EPR）和高压用于深入了解相关的静态各向异性相互作用，而脉冲EPR用于探测动态特性，包括自旋-自旋和自旋-晶格弛豫。国家高磁场实验室提供的仪器使研究能够跨越前所未有的场和频率范围，为分子纳米磁学社区中当前感兴趣的许多材料打开了这一强大的技术。与化学家的紧密合作提供了一个非常需要的反馈回路，具有在分子基磁性材料方面取得重大进展的潜力。

Non-technical Abstract:This highly interdisciplinary project involves the study of magnetic molecules whose properties can be chemically engineered at the molecular level to give desired physical properties. These so-called molecular nanomagnets provide remarkable fundamental insights into magnetism at the nanoscale, while promising important advances in information technologies. In this regard, two distinct thrusts are under investigation: the first involves the potential use of magnetic molecules as the elementary memory units (bits) in classical computers, where the information is stored in the magnetic polarization state (up or down) of the molecule; the second explores the possibility of exploiting the quantum states of such molecules to implement quantum computing algorithms. This project employs unique magnetic resonance spectroscopic techniques that have been developed by the PI at the US National High Magnetic Field Laboratory to establish structure-property relations that chemists can then use to optimally design molecules for targeted applications. Although the design criteria for classical and quantum memories (qubits) are somewhat different, at a fundamental level, they typically involve tuning/optimizing the same interactions in molecular systems. The research team is exploring how the choice of magnetic element, molecular geometry, and surrounding host material influence the stability of both classical and quantum information encoded into magnetic molecules. The team is also researching possibilities for "wiring" magnetic molecules together using organic linkers. Results obtained from the project are of interest to other research communities, including materials science, inorganic and bioinorganic chemistry. The PI is strongly committed to diversity, both in terms of student recruitment, and through active participation in the American Physical Society's Masters-to-PhD Bridge Program and National Mentoring Community.Technical Abstract:The molecular nanomagnetism field has witnessed remarkable progress during the past few years, e.g.: a four-fold increase in the temperature below which a magnetic molecule can retain its magnetization has been achieved; and the coherent manipulation and readout of a single Tb nuclear spin has been demonstrated in a molecular device. Crucial to both of these results has been a focus on simple molecules comprised of magnetic ions with strong spin-orbit anisotropy. Recent activity has seen a bifurcation into distinct thrusts: the first continues to focus on single-molecule magnets (SMMs) that can function as classical memory elements; the 2nd thrust involves the potential use of molecular nanomagnets in quantum computing applications. This project addresses both areas. Work on SMMs focuses on: (i) anisotropic spin-orbit mediated exchange involving orbitally degenerate transition metals coupled to one or two additional high-spin centers; and (ii) direct exchange between anisotropic lanthanides using spin bearing (radical) ligands. The aim in both cases is to obtain simple, yet highly anisotropic molecules (dimers and trimers), which have sufficiently large spin ground states to shut down quantum tunneling and spin-lattice relaxation pathways that prevent magnetization blocking. Meanwhile, (iii) work on spin qubits focuses on anisotropic mononuclear species in which crystal field states can be engineered that protect against dipolar spin-spin decoherence. In this situation, spin-lattice relaxation can end up limiting phase memory times. High-field/frequency electron paramagnetic resonance (EPR) and high pressures are used to gain insights into the relevant static anisotropic interactions, while pulsed EPR is employed to probe dynamical properties, including spin-spin and spin-lattice relaxation. Instruments available at the National High Magnetic Field Laboratory enable studies spanning unprecedented field and frequency ranges, opening up this powerful technique to many materials of current interest within the molecular nanomagnetism community. Strong collaboration with chemists provides a much needed feedback loop, with the potential for major advances in molecule-based magnetic materials.