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DEFECTS IN FRUSTRATED SYTEMS

受挫系统中的缺陷

基本信息

批准号：
EP/G004765/1
负责人：
William Branford
金额：
$ 123.64万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FG004765%2F1
关键词：
DEFECTS FRUSTRATED SYTEMS

项目摘要

In a complex system made up of many smaller units, each element will interact with all of its neighbours, and the system tries to arrange itself so that the most favourable bond is formed with each neighbour. However, sometimes the neighbours have requirements that are mutually incompatible and a compromise must be found. If this is the case we describe the system as being frustrated. Frustration occurs widely in nature and is thought to be critical to our understanding of such questions as how do our brains work? and how do proteins fold? The frustrated biological systems described are so complex and so important that the science of frustration has become a major research area and there is great demand for simpler model systems where the interaction strength can be tuned, the model system size can be varied, defects can be introduced in a controlled manner and individual elements can be manipulated, removed or their individual state recorded. In such an ideal system one could unite theory and experiment and begin to understand the underlying physics within this complexity. Magnetic frustration has proved to be the most successful area for finding model systems. Traditionally these were magnetic crystals prepared by solid-state chemistry. However it has recently been shown that it is possible to use nanotechnology to make arrays of magnetic bars sufficiently small and sufficiently close together that the magnetic interactions between them becomes very significant, and that novel geometries can be designed where the magnetic interactions cannot all be satisfied. This development opens up broad new avenues of research in model frustrated systems. In solid-state chemistry one is limited by nature in the geometrical arrangements that are possible, whereas with nanotechnology any pattern that will tessellate can be fabricated into an array, on any length-scale down to the minimum feature size of the lithography. Here I propose to study such ideal systems that are based on frustrated magnetic nanostructures. Our experience from frustrated magnetic chemical structures tells us that triangles and hexagons are the building blocks that favour magnetic frustration. The initial work was done on arrays of magnetic bars that were isolated from one another, but I plan to focus on electrically continuous lattices, such as the hexagonal honeycomb structure so that electrical current can pass through it. The electrical properties of magnetic materials are sensitive to the magnetic structure and so this gives a direct probe of the frustrated structure and one can study its dynamic response to changes in temperature and magnetic field. Magnetic force microscopy (MFM) and scanning Hall probe imaging will be used to image the magnetic structure during these experiments. These in-situ measurements will allow the change in electrical response to be correlated directly with the change in magnetic structure, and will provide important information of the nature of the coupling between the magnetic and electrical properties of ferromagnetic metals, and the role of topology, which is currently very important for new spin-based electronics or spintronics technology. In addition to improving knowledge of diverse other fields, the magnetic arrays that I will make are exciting in their own right. Their unusual and sensitive response to magnetic fields might be useful in sensors. Furthermore the strong coupling between all the elements, and the fact that the magnetic state of individual elements can be both written (changed by applying a magnetic field) and read, means they could potentially be used for novel types of computation, often described as neural networks because they work more like the brain than like a conventional computer.

在一个由许多较小的单元组成的复杂系统中，每个元素都会与其所有的邻居相互作用，并且系统试图安排自己，以便与每个邻居形成最有利的联系。然而，有时邻国有互不相容的要求，必须找到一种妥协。如果是这种情况，我们将系统描述为受挫。挫折在自然界中广泛存在，并且被认为对我们理解大脑如何工作等问题至关重要。蛋白质是如何折叠的？所描述的受挫生物系统是如此复杂和重要，以至于受挫科学已经成为一个主要的研究领域，并且对更简单的模型系统有很大的需求，在这些模型系统中，相互作用的强度可以调整，模型系统的大小可以改变，缺陷可以以可控的方式引入，单个元素可以被操纵，移除或记录它们的个体状态。在这样一个理想的系统中，人们可以把理论和实验结合起来，并开始理解这种复杂性中的潜在物理学。磁阻已被证明是寻找模型系统最成功的领域。传统上，这些都是由固态化学制备的磁性晶体。然而，最近的研究表明，利用纳米技术制造足够小、足够紧密的磁棒阵列是可能的，它们之间的磁相互作用变得非常显著，并且可以设计出新的几何形状，使磁相互作用不能全部得到满足。这一发展为模型受挫系统的研究开辟了广阔的新途径。在固态化学中，一个人受限于可能的几何排列，而在纳米技术中，任何图案都可以镶嵌成一个阵列，在任何长度尺度上，小到光刻的最小特征尺寸。在这里，我建议研究这种基于受挫磁性纳米结构的理想系统。我们从受挫的磁性化学结构中获得的经验告诉我们，三角形和六边形是有利于磁性受挫的构建块。最初的工作是在相互隔离的磁棒阵列上完成的，但我计划把重点放在电连续的晶格上，比如六边形蜂窝结构，这样电流就可以通过它。磁性材料的电性能对磁性结构非常敏感，因此可以直接探测磁性结构，并可以研究其对温度和磁场变化的动态响应。在这些实验中，将使用磁力显微镜（MFM）和扫描霍尔探针成像对磁性结构进行成像。这些原位测量将使电响应的变化与磁结构的变化直接相关，并将提供铁磁性金属的磁和电性质之间耦合的性质的重要信息，以及拓扑的作用，这对于目前新的基于自旋的电子学或自旋电子学技术非常重要。除了提高其他不同领域的知识，我将制作的磁阵列本身就令人兴奋。它们对磁场异常敏感的反应可能在传感器中有用。此外，所有元素之间的强耦合，以及单个元素的磁性状态既可以写入（通过施加磁场改变）又可以读取的事实，意味着它们可能被用于新型计算，通常被称为神经网络，因为它们的工作方式更像大脑而不是传统的计算机。