CAREER: Study of Degeneracy Breaking Effects and Emergent Phenomena in Heterostructures of Frustrated Antiferromagnets

非技术摘要：今天的高科技社会在很大程度上依赖于电子产品，如计算机，它们利用电荷（电子）的运动来工作。电子还有另一个特性，它的自旋（即转动动量）。在大多数磁性材料中，这些自旋整齐地排列在原子核的重复模式上。在装饰冰箱的铁磁体中，所有这些自旋都沿同一方向排列，使材料具有明确的北极和南极。研究小组研究的是原子核呈三角形排列的奇异磁体，在这种情况下，自旋无法决定指向哪里。这允许系统不是只采用一种状态，而是在许多可用状态之间波动。与这些波动相关的“自旋翻转”可以被视为只有一个磁极的粒子。该项目的主要主题之一是研究这些自旋翻转是否可以用作未来几代信息技术（如量子计算）的信息载体。研究小组在佛罗里达州立大学和国家高磁场实验室（NHMFL）以薄膜形式合成了这些奇异的磁铁。通过拉伸薄膜材料，首席研究员调整原子位置和磁性，这些都是在NHMFL和国家实验室使用最先进的设备进行研究的。这项工作对于未来基于奇异磁性材料的设备利用自旋而不是电荷作为信息载体铺平了道路。这些研究目标与材料合成的本科课程开发相结合，为佛罗里达州立大学的学生提供教育，使他们为新兴的先进材料劳动力做好准备。推广工作包括公共讲座和中学课堂活动，旨在增加社区内的（材料）科学资本。通过这些活动，首席研究员致力于提高学生的科学意识和兴趣，并使他们能够对未来的职业道路做出更明智的决定。技术摘要：本项目旨在研究暴露于简并破缺微扰的几何受挫系统中的基态选择、涌现特性和伴随的奇异激发。强自旋/晶格耦合有望导致结构工程薄膜和受挫反铁磁体异质结构中的涌现基态。最初的重点是焦绿钛酸盐，几何上受挫的系统，伊辛各向异性导致自旋冰态的形成，只显示出短期的相关性。自旋冰态已被证明具有类似磁单极子的拓扑激发。利用拓扑激发（如单极子）作为新型信息载体具有诱人的潜力。该项目旨在描述自旋冰的物理特性，以及单极子的形成和动力学，如何响应外部扰动，如外延应变。此外，应变在薄膜样品中的应用不可避免地导致了维数的降低，并且这种约束对自旋冰物理的影响预计是显著的，目前正在研究中。自旋冰物理在尖晶石钒酸盐中也被观察到，尖晶石钒酸盐是受挫反铁磁体轨道物理的海报材料。PI利用外延应变来调整非共线自旋织构，并稳定了钒尖晶石薄膜中焦绿石V亚晶格上自旋冰态的d电子模拟。与本项目相关的活动的一般方法可以描述为：1)系统地合成和表征受挫反铁磁体的应变薄膜；2)表征磁性和相关的非共线自旋织构，使用电容转矩磁强计测量和弹性中子散射研究；3)发展扭矩技术，包括探测尖晶石和焦绿石薄膜中自旋翻转动力学的能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:Today's high tech society relies heavily on electronics such as computers, which use the movement of charge (electrons) to function. The electron has another property, its spin (i.e., rotational momentum). In most magnetic materials these spins are neatly arranged on a repeating pattern of atomic nuclei. In ferromagnets, the kind of magnets that decorate fridges, all these spins are aligned in the same direction, making the material magnetic with a well-defined north and south pole. The research team works on exotic magnets with atomic nuclei arranged in triangular patterns in which the spins cannot make up their minds about where to point. This allows the system to not adopt just one state but rather fluctuate between many available states. The "spin flips" associated with these fluctuations can be regarded as particles that have only a single magnetic pole. One of the major themes of this project is to investigate whether these spin flips can be used as information carriers in future generations of information technology, such as quantum computing. The research team synthesizes these exotic magnets in thin film form at Florida State University and the National High Magnetic Field Laboratory (NHMFL). By straining the thin film material the principal investigator tweaks the atomic positions, and the magnetic properties, which are studied using state-of-the-art facilities at the NHMFL and at national laboratories. This work is paramount in paving the way to a future in which devices based on exotic magnetic materials make use of spins, rather than charges, as information carriers. These research goals are integrated with undergraduate level curriculum development in materials synthesis to provide students at Florida State University with an education that will prepare them for the emerging advanced materials workforce. Outreach efforts include public lectures and middle school classroom activities that aim to increase (materials) science capital within the community. With these activities the principal investigator works to increase science awareness and interest in students and to empower them to make more informed decisions about their future career paths. Technical abstract:This project seeks to study ground state selection, emergent properties, and concomitant exotic excitations in geometrically frustrated systems as they are exposed to degeneracy breaking perturbations. Strong spin/lattice coupling is expected to lead to emergent ground states in structurally engineered films and heterostructures of frustrated antiferromagnets. The initial focus is on pyrochlore titanates, geometrically frustrated systems in which the Ising anisotropy leads to formation of a spin ice state showing only short range correlations. The spin ice state has been shown to host topological excitations that behave like magnetic monopoles. There is an enticing potential of harnessing topological excitations, such as monopoles, as novel types of information carriers. The project is aimed at characterizing how the spin ice physics, and the formation and dynamics of the monopoles, respond to external perturbations such as epitaxial strain. Furthermore, the application of strain in thin film samples unavoidably leads to a reduction in dimensionality, and the effect of such confinement on spin ice physics, which is predicted to be significant, is being investigated. Spin ice physics is also observed in spinel vanadates, poster materials for orbital physics in frustrated antiferromagnets. The PI utilizes epitaxial strain to tune noncollinear spin textures and stabilize a d-electron analogue of the spin ice state on the pyrochlore V sublattice in spinel vanadate thin films. The general approach for activities associated with this project can be described as, 1) systematic synthesis and structural characterization of strained thin films of frustrated antiferromagnets, 2) characterization of the magnetic properties, and associated noncollinear spin textures, using capacitive torque magnetometry measurements and elastic neutron scattering studies, and 3) development of the torque technique to include the ability to probe spin flip dynamics in spinel and pyrochlore thin films.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.