Exploring The Topological Magnetic Excitation Spectrum Of S=half MOFs With Inelastic Neutron Scattering

利用非弹性中子散射探索 S=half MOF 的拓扑磁激发谱

• 批准号: 2910699
• 金额: --
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2910699
• 关键词: Exploring; Topological; Magnetic; Excitation; Spectrum

Metal-Organic Frameworks (MOFs) are a hot topic in the research community across a range of disciplines including solid state chemistry, condensed matter physics and materials science. In my project, kagomé MOFs offer a valuable pathway to synthetically realise two-dimensional magnetic models whilst simultaneously remaining advantageous over purely inorganic systems due to the ability to avoid the atomic site disorder. In our kagomé systems, the magnetism arises from Cu2+ ions forming the corners of the kagomé lattice, making our systems S=half. Such systems are ferromagnetic (FM) when entire layers align parallel with one another. Antiferromagnetism (AFM) is typically when moments align antiparallel to one another, although the structure of the kagomé net renders this difficult due to magnetic frustration. Materials that are magnetically frustrated in their ground state, with S=1/2 kagomé AFMs as an example, are known as quantum spin liquids (QSLs). The in-plane FM or AFM interactions can provide the system with a characteristic topological magnetic excitation spectrum, giving rise to interesting properties such as the magnon Hall effect and chiral edge modes. However, this spectrum can be affected by interplanar interactions and therefore it is particularly useful for us to deal with MOFs as varying the linker can influence the nature and strength and presence of these interplanar interactions. Currently, research in this area remains in its 'blue skies' phase, although it is thought that these systems can be used for electronic and spintronic devices in quantum computing for low energy data storage. Although the first S= half kagomé FM has been synthesised in the past decade, fully understanding the topological magnetic excitation spectrum is yet to be achieved and remains one of the aims of my current research. QSLs are particularly elusive to synthesise, and no system of this type has been experimentally realised to date. The Clark group has synthesised a S=half kagomé AFM MOF which we believe is a good QSL candidate, although several complimentary techniques are required to unambiguously determine this, which will form part of my research in due course. Such techniques include x-ray and neutron diffraction, muon spectroscopy, inelastic neutron scattering (INS) and magnetometry measurements.The major component of my research so far has included analysing preliminary data sets from INS measurements taken at the international facility, ISIS. INS can reveal information about the magnetic band structure of a material. This is analogous to how electronic band structure can influence the properties of a material. For example, a band gap in the electronic band structure gives rise to a material having insulating properties as electrons cannot hop across this distance to conduct the charge carried by these electrons. Furthermore, the relative size and nature (FM or AFM) of the magnetic interactions with one another can impact the appearance of this spectrum and therefore tell us about the nature of the exhibited magnetism. This analysis has required constructing a Python code to fit our data to a given model and comparing to simulations using a MATLAB library known as SpinW. I will also be directly involved in the synthesis of these systems to take them on beamtime experiments at these international facilities.

金属有机骨架(MOF)是固体化学、凝聚态物理和材料科学等多个学科的研究热点。在我的项目中，KagoméMOF提供了一条有价值的途径来综合实现二维磁性模型，同时由于能够避免原子位无序，因此保持了相对于纯无机体系的优势。在我们的Kagomé系统中，磁性来自形成Kagomé晶格拐角的Cu2+离子，使我们的系统S=一半。当整个层彼此平行排列时，这样的系统就是铁磁性的(FM)。反铁磁性(AFM)通常是当力矩彼此反平行排列时，尽管Kagoménet的结构由于磁性受挫而使这一点变得困难。以S=1/2 KagoméAFM为例，在基态受到磁阻的材料被称为量子自旋液体(QSL)。面内FM或AFM相互作用可以为系统提供特征的拓扑磁激发谱，从而产生磁振子霍尔效应和手征边缘模等有趣的性质。然而，这种光谱会受到面间相互作用的影响，因此它对我们处理MOF特别有用，因为不同的连接基可以影响这些面间相互作用的性质、强度和存在。目前，这一领域的研究仍处于“蓝天”阶段，尽管人们认为这些系统可以用于量子计算中的电子和自旋电子器件，用于低能量的数据存储。虽然在过去的十年里已经合成了第一个S=Half KagoméFM，但对拓扑磁激发谱的充分理解还没有实现，这仍然是我目前研究的目标之一。QSL的合成尤其难以捉摸，到目前为止还没有这种类型的系统被实验实现。克拉克团队已经合成了一个S=Half kagoméAFM MOF，我们认为它是一个很好的QSL候选者，尽管需要几项互补的技术才能明确地确定这一点，这将成为我稍后研究的一部分。这些技术包括X射线和中子衍射、介子光谱、非弹性中子散射(INS)和磁学测量。到目前为止，我研究的主要部分包括分析国际设施ISIS的INS测量的初步数据集。INS可以揭示一种材料的磁带结构信息。这类似于电子能带结构如何影响材料的性质。例如，电子能带结构中的带隙导致具有绝缘性能的材料，因为电子不能跨越这一距离来传导这些电子携带的电荷。此外，磁相互作用的相对大小和性质(FM或AFM)可以影响光谱的外观，从而告诉我们所展示的磁性的性质。这种分析需要构建一个Python代码来将我们的数据与给定的模型相匹配，并与使用名为SpinW的MatLab库进行的模拟进行比较。我还将直接参与这些系统的合成，以便在这些国际设施中进行波束时间实验。