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

非技术摘要：当今的高科技社会严重依赖于电子产品，如计算机，它使用电荷（电子）的运动来运行。电子具有另一种性质，即它的自旋（即，旋转动量）。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图案上。在铁磁体中，这种装饰冰箱的磁体，所有这些自旋都在同一个方向上排列，使材料具有明确的北极和南极。该研究小组研究的是具有三角形排列的原子核的奇异磁体，其中自旋无法决定指向何处。这允许系统不采用仅一个状态，而是在许多可用状态之间波动。与这些涨落相关的“自旋翻转”可以被看作是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在未来几代信息技术中用作信息载体，例如量子计算。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。通过对薄膜材料进行应变，首席研究员调整了原子位置和磁性，并使用NHMFL和国家实验室的最先进设施进行了研究。这项工作是至关重要的铺平道路，未来的设备基于外来磁性材料利用自旋，而不是电荷，作为信息载体。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。推广工作包括公开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：该项目旨在研究几何挫折系统中的基态选择，涌现特性和伴随的奇异激发，因为它们暴露于简并破缺扰动。 强自旋/晶格耦合预计将导致紧急基态的结构工程薄膜和异质结构的挫折反铁磁体。最初的重点是烧绿石钛酸盐，几何受挫系统中的伊辛各向异性导致形成的自旋冰状态，只显示短程相关性。自旋冰态已经被证明是拓扑激发的宿主，表现得像磁单极子。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物理学以及单极子的形成和动力学如何对外延应变等外部扰动作出反应。此外，应变在薄膜样品中的应用必然导致维数的降低，并且正在研究这种限制对自旋冰物理的影响，预计这将是重要的。在尖晶石钒酸盐中也观察到了自旋冰物理，尖晶石钒酸盐是受挫反铁磁体中轨道物理的海报材料。PI利用外延应变调整非共线自旋纹理和稳定的d-电子模拟的自旋冰状态的烧绿石V亚晶格尖晶石钒酸盐薄膜。与该项目相关的活动的一般方法可以描述为，1）受抑反铁磁体的应变薄膜的系统合成和结构表征，2）磁性的表征，以及相关的非共线自旋织构，使用电容扭矩磁力测量和弹性中子散射研究，和3）该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的评估，被认为是值得支持的。影响审查标准。

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.