Scalable Magnetic Anisotropy from Molecular Lanthanide Building Units

非技术概述：设计新的功能材料的一种现代方法是通过构建和连接分子结构单元。在这种方法中，化学家们合成具有结构的分子，当这些结构连接在一起形成块状材料时，就会产生具有特定性质的材料。通过对分子构筑单元的修饰，可以简单地引入和调节新的性质。以此类推，可以从砖和砂浆开始设计无限数量的结构，而不是从单个预制的烧制粘土平板开始设计一个结构。构建块方法仍然是一个挑战的合成领域是磁性材料。磁性材料几乎是现代生活方方面面的重要组成部分，但只有少数材料满足应用要求，而且这些材料都不是通过分子结构单元方法制造的。相互作用的复杂性决定了磁矩想要对齐的方向(其磁各向异性)，这导致了制造材料的困难。当分子建筑单元连接在一起时，新的相互作用会破坏它们各自的磁各向异性，极大地削弱它，并摧毁与原始建筑单元的各向异性的任何合理联系。回到结构上的类比，将分子磁体连接起来制造块状磁体通常类似于使用砖，这些砖在堆叠时会自发地变成原始粘土。为了改变这一点，在NSF固态和材料化学计划和化学结构、动力学和机制B计划的支持下，加州大学圣迭戈分校的研究人员正在开发分子构建单元，这些单元在连接形成扩展的磁性材料时保持其巨大的各向异性值。这类新材料是由含有稀土离子Er3+的单个单元组成的，研究人员可以创造出模仿固态化学中稀有和难以研究的主题的设计磁性结构，或者通过设计创造出全新的磁性结构。此外，该项目通过创新的方法教育研究生和本科生，例如以实验室参观和演示为特色的现场直播，以加强课堂教学。技术摘要：只有控制电子自旋的首选取向(其磁各向异性)，才能实现对磁性材料的分子构建单元方法。在NSF固态和材料化学计划和化学结构、动力学和机制B计划的支持下，该项目确定了能够在存在构建磁性材料所需的分子间连接的情况下控制各向异性的分子构建块。在单离子水平上产生和固定磁各向异性，将研究的重点转移到合理设计复杂的自旋几何结构、增强磁耦合和扩展维度。通过将镧系元素与其特定的、合适的晶场环境相结合来产生强各向异性磁性的设计原则已被很好地理解。然而，在引入耦合相互作用的同时保持这种各向异性是一个复杂的挑战。一种方法是确定一个单一的配体-稀土元素组合，该组合可以引导各向异性，大致独立于配位球的其余部分。通过计算和实验结果，研究人员已经证明，Er(III)与环八碳四烯二阴离子之间的相互作用满足大致固定各向异性的磁性构筑单元的要求。在这个项目中，加州大学圣迭戈分校的研究人员使用分子磁构建单元来探测在交换和磁偶极耦合存在的情况下各向异性自旋的行为，这使他们能够构建新的磁体并独立调整系统参数，这在任何其他类型的材料中都是不存在的。固定两个位置的各向异性和增强交换相互作用可以在离子之间产生更强和可切换的磁相互作用。更复杂的一维到三维自旋结构是从这些分子构建块创建的，这些结构探索了磁场强度的极限。该系统的每个方面，从耦合各向异性和强度到连接性和维度，都允许对一系列基本磁性现象进行受控研究-通常以传统氧化物或金属间磁性材料无法调节或不实用的方式进行。虽然自旋电子技术已经变得无处不在，但它几乎完全基于自上而下的方法。基于分子的材料提供了增强的可调性、终端可伸缩性、自组装和独特的量子限制特性，这些特性与NSF大想法类别：量子飞跃的目标很好地一致。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical summary:One modern approach to the design of new functional materials is through the construction and connection of molecular building units. In this approach, chemists synthesize molecules with structures that, when linked together to form a bulk material, lead to a material with specific properties. New properties can be introduced and tuned simply through modification of the molecular building unit. By analogy, a limitless number of structures can be designed starting with bricks and mortar, as opposed to one structure from a single pre-formed slab of fired clay. An area of synthesis where the building block approach remains a challenge is magnetic materials. Magnetic materials are vital components in nearly every aspect of modern life, yet only a handful of materials meet the requirements for use in applications, and none of these are made through a molecular building unit approach. The complexity of interactions that determine what direction the magnetic moment wants to align (its magnetic anisotropy) contributes to the difficulties in making the materials. As molecular building units are connected, new interactions disrupt their individual magnetic anisotropy, drastically weakening it and destroying any rational connection with the anisotropy of the original building unit. Returning to the construction analogy, connecting molecular magnets to make a bulk magnet is often akin to using bricks that spontaneously become raw clay when stacked. To change this, with support from the Solid State and Materials Chemistry program and the Chemical Structure, Dynamics and Mechanisms B program at NSF, researchers at UCSD are developing molecular building units that retain their large anisotropy values when connected to form an extended magnetic material. This class of new materials, built from individual units containing a rare earth ion, Er3+, allows the researchers to create designer magnetic structures that mimic rare and difficult-to-study motifs from solid state chemistry or create entirely new magnetic structures by design. Additionally, this project educates graduate and undergraduate students through innovative approaches such as a "In the Lab" live-feed featuring lab tours and demonstrations to enhance classroom teaching.Technical summary:A molecular building unit approach to magnetic materials can be realized only if the preferred orientation of the electron spin (its magnetic anisotropy) can be controlled. With this project, supported by the Solid State and Materials Chemistry program and the Chemical Structure, Dynamics and Mechanisms B program at NSF, molecular building blocks are identified that are capable of controlling anisotropy in the presence of the intermolecular linkages necessary to construct magnetic materials. Generating and fixing the magnetic anisotropy at the single-ion level, shifts research efforts to the rational design of complex spin geometries, enhanced magnetic coupling, and expanded dimensionality. The design principles for creating strongly anisotropic magnetism by combining a lanthanide with its specific, suitable crystal-field environment are well understood. Maintaining this anisotropy while introducing coupling interactions, however, is a complex challenge. One approach is to determine a single ligand-lanthanide combination that can direct the anisotropy roughly independent of the rest of the coordination sphere. Through computational and experimental results researchers have previously shown that the interaction between Er(III) and the cyclooctatetraenide dianion fulfills the requirements of a magnetic building unit of roughly fixed anisotropy. In this project researchers at UCSD use the molecular magnetic building unit to probe the behavior of anisotropic spins in the presence of both exchange and magnetic dipolar coupling, which enables them to construct new magnets and to independently tune system parameters, unavailable in any other class of materials. Fixing the two-site anisotropy and enhancing the exchange interaction creates stronger and switchable magnetic interactions between ions. More complex 1- to 3-dimensional spin structures that explore the limits of magnetic strength are created from these molecular building blocks. Each aspect of the system, from the coupling anisotropy and strength to the connectivity and dimensionality, allows the controlled study of an array of fundamental magnetic phenomena - often in ways that are not tunable or practical in traditional oxide or intermetallic magnetic materials. While spintronic technology has become ubiquitous, it is almost exclusively based on top-down approaches. Molecule-based materials offer the promise of enhanced tunability, terminal scalability, self-assembly, and unique quantum-confinement properties that align well with the goals of the NSF Big Ideas category: Quantum Leap.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.