Probing Effects of Pressure, Mixed Valence, and Spin Frustration on Itinerant Magnets

第一部分：非技术总结本项目重点调查巡回磁铁，这是一种独特的材料，用于具有重要社会意义的清洁能源技术，包括电动汽车、风力涡轮机和磁性冰箱。早期的研究提供了对简单金属--铁、钴和镍--磁性的理解。然而，目前，材料科学家可用的知识和理论工具的状态使人们能够洞察由两个或更多元素组成的更复杂的金属间化合物系统的磁性行为。该项目由材料研究部的固态和材料化学项目支持，将把先进的理论方法与巡回磁体的实验研究结合起来。化学合成、外加压力和强磁场将被用来触发磁性行为的变化。对观察到的变化的详细分析将确定巡回磁铁如何对其晶体和电子结构的变化做出反应。这些研究的结果将是增进对巡回磁铁的了解，以设计用于清洁能源技术和其他应用的先进磁性材料。该项目采用的理论和实验工具的多样性将为研究生和本科生提供独特的研究培训，他们将精通固态化学、材料合成和表征以及量子化学计算。为了更广泛的推广，PI项目还将在全国范围内组织磁性和磁性材料的本科生暑期学校。第二部分：技术总结几十年来，磁性一直是凝聚态物理的一个迷人的研究领域。然而，目前，由于研究电子结构的理论工具的广泛可用以及对固体中化学键特性的深入了解，这类磁性系统正受到固体化学家的重新关注。该项目旨在通过探索晶体和电子结构与磁性之间的相互作用，揭示巡回磁体中磁有序的性质和化学键之间的关联，作为化学替代、外加压力或磁场的函数。该项目的一个方面将集中在复杂的过渡金属化合物上，重点是压力和光诱导激发的影响，这些激发可能导致金属行为的剧烈变化。该项目还将研究具有金属键或强共价键的自旋受挫系统的行为。这些研究的目标是自旋受挫系统的下一级复杂性，其中巡回磁行为的添加可以导致发现奇异的自旋织构和非传统的自旋动力学。拟议的研究活动将为研究生和本科生提供材料合成、结构和磁性调查以及电子能带结构研究方面的综合培训。本科生和来自代表性不足群体的学生将作为研究人员参与该项目，并通过参加由国际磁学协会组织的全国磁性和磁性材料本科暑期学校。该项目由材料研究部的固态和材料化学项目支持。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。

PART I: NON-TECHNICAL SUMMARYThis project focuses on investigation of itinerant magnets, a unique class of materials used in societally important clean-energy technologies, including electric vehicles, wind turbines, and magnetic refrigerators. Early studies offered understanding of magnetism in simple metals -- iron, cobalt, and nickel. Currently, however, the state of knowledge and theoretical tools available to materials scientists affords insight into magnetic behavior of more complex intermetallic systems, consisting of two or more elements. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, will combine advanced theoretical methods with experimental studies of itinerant magnets. Chemical synthesis, applied pressure, and high magnetic fields will be used to trigger changes in magnetic behavior. A detailed analysis of the changes observed will establish how itinerant magnets respond to variations in their crystal and electronic structures. The outcome of these studies will be improved understanding of itinerant magnets for the design of advanced magnetic materials to be used in clean-energy technologies and other applications. The diversity of theoretical and experimental tools employed in this project will provide unique research training for graduate and undergraduate students, who will become proficient in solid state chemistry, materials synthesis and characterization, and quantum-chemical calculations. For broader outreach, the project PI will also organize nationwide undergraduate summer schools in magnetism and magnetic materials.PART II: TECHNICAL SUMMARYItinerant magnetism has been a fascinating area of research in condensed-matter physics for many decades. Currently, however, such magnetic systems are receiving renewed attention from solid-state chemists, due to the broader availability of theoretical tools for investigation of electronic structure and improved insight into peculiarities of chemical bonding in the solid state. This project aims to uncover correlations between the nature of magnetic ordering and chemical bonding in itinerant magnets by exploring the interplay between the crystal and electronic structure and magnetic properties as a function of chemical substitution, applied pressure, or magnetic field. One aspect of the project will focus on complex transition metal pnictides, with an emphasis on effects of pressure and light-induced excitations that may lead to drastic changes in metallic behavior. The project will also investigate behavior of spin-frustrated systems with metallic or strongly covalent bonding. These studies target the next level of complexity in the spin-frustrated systems, where the addition of itinerant magnetic behavior can lead to the discovery of exotic spin textures and unconventional spin dynamics. The proposed research activities will provide versatile training to graduate and undergraduate students in materials synthesis, investigation of structural and magnetic properties, and studies of the electronic band structure. Undergraduate students and students from underrepresented groups will be involved in the project, both as researchers and through participation in national undergraduate summer schools in magnetism and magnetic materials organized by the PI. This project is supported by the Solid State and Materials Chemistry program in the Division of Materials Research.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.