Artificial Spin Ice: Designer Matter Far From Equilibrium

人造旋转冰：设计问题远离平衡

• 批准号: EP/L002922/1
• 负责人: Robert Stamps
• 金额: $ 62.81万
• 依托单位: University of Glasgow
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FL002922%2F1
• 关键词: Artificial; Spin; Ice; Designer; Matter

Our project is a collaborative one between two Universities and a national laboratory working together across a combined theoretical and experimental programme. The experiments are based in both conventional laboratories and large-scale facilities. The work programme also involves continued international collaboration with colleagues in the US at Brookhaven National Laboratory, who have helped us make some of our most recent breakthroughs in creating and understanding nanostructured magnets, as well as adding new ones in the form of the unique expertise and facilities available for transmission x-ray imaging at the Advanced Light Source in Berkeley. Both of these are DOE-supported US national laboratories.Our goal is to understand and control non-equilibrium dynamics in a new class of magnetic materials: strongly correlated arrays of sub-micron sized magnets. Examples have been studied recently, and given the name "artificial spin ice". These materials are important examples of new metamaterials with unique properties not realised in naturally occurring magnetic materials. The artificial magnetic ice are systems composed of strongly interacting magnetic moments, and the moments are arranged geometrically in order to produce metastable configurations with a high degree of degeneracy in energy. We will use artificial spin ice as a paradigm for a systematic exploration of non-equilibrium dynamics. This is a model system for which the free energy is specified by design and hence completely determined, and the exact microstate--and its evolution in time--can be observed directly for detailed comparison with mathematical predictions. Inter-element interactions can be specified to a large extent by design through control of geometry. In this way it is possible to create competitions between ordering that result in geometrical frustrations responsible for complex response to applied magnetic fields. The resulting magnetic properties are analogous to those of traditional thin film or bulk magnetic systems, but with key differences that can be of especial importance for applications. For example, there are two ground state configurations in a square ice that form domains with zero net moment. These are separated by magnetised boundary walls along which magnetic charges can move.Magnetic charges (sometimes called emergent monopoles) are of particular interest since they can be readily detected and can be moved through an array by applied magnetic fields. We will develop methods to inject and detect charges, and control their flow through array geometries. Our goal is to identify structures and techniques for the design of circuits through which "magnetricity" can flow and be usefully employed for technological applications. Our idea is to use thermal fluctuations to aid magnetic charge mobility. We can do this by using nanoscale particles in our arrays, such that the particles are near their superparamagnetic blocking temperature. An important distinction with prior work is that we shall use materials with phase transitions close to room temperature to allow us to tune simply between thermally equilibrated and athermal non-equilibrium states. This will mean that the individual moments can reverse spontaneously, thus enabling thermally driven motion of magnetic charges through a fluctuating array. Through a combination of applied fields and temperature control we will be able to start, stop, and direct magnetic charge dynamics. These systems may also give us new experimental models for studies of critical dynamics at phase transitions since they can be modelled by well known exactly soluble Ising systems, as well as providing new paradigms for information processing architectures.

我们的项目是两所大学和一个国家实验室之间的合作项目，通过理论和实验相结合的方式共同努力。实验在传统实验室和大型设施中进行。工作计划还包括与美国布鲁克海文国家实验室的同事进行持续的国际合作，他们帮助我们在创建和理解纳米结构磁铁方面取得了一些最新突破，并以独特的专业知识和设施的形式增加了新的形式，可用于传输x射线成像在伯克利的先进光源。这两个实验室都是美国能源部支持的美国国家实验室。我们的目标是理解和控制一种新型磁性材料的非平衡动力学：亚微米大小的强相关磁体阵列。最近研究了一些实例，并将其命名为“人工自旋冰”。这些材料是具有独特性能的新型超材料的重要例子，这些特性在天然磁性材料中是无法实现的。人工磁冰是由强相互作用的磁矩组成的系统，这些磁矩是几何排列的，以产生具有高度能量简并的亚稳态构型。我们将使用人工自旋冰作为非平衡动力学系统探索的范例。这是一个模型系统，其自由能是由设计指定的，因此是完全确定的，精确的微观状态及其随时间的演变可以直接观察到，以便与数学预测进行详细的比较。元素间的相互作用可以在很大程度上通过几何控制设计来指定。通过这种方式，有可能在排序之间产生竞争，从而导致对外加磁场的复杂响应的几何挫折。由此产生的磁性与传统的薄膜或体磁性系统类似，但在应用中具有特别重要的关键差异。例如，方形冰中有两种基态构型，它们形成净力矩为零的域。它们被磁化的边界墙隔开，磁荷可以沿着边界墙移动。磁荷（有时称为涌现单极子）特别有趣，因为它们可以很容易地检测到，并且可以通过外加磁场在阵列中移动。我们将开发注入和检测电荷的方法，并通过阵列几何形状控制它们的流动。我们的目标是确定电路设计的结构和技术，通过这些结构和技术，“磁性”可以流动，并有效地用于技术应用。我们的想法是利用热波动来帮助磁荷迁移。我们可以通过在我们的阵列中使用纳米级粒子来做到这一点，这样这些粒子就接近它们的超顺磁阻塞温度。与先前工作的一个重要区别是，我们将使用相变接近室温的材料，使我们能够简单地在热平衡和非热平衡状态之间进行调整。这将意味着单个矩可以自发地反转，从而使磁荷通过波动阵列的热驱动运动成为可能。通过应用磁场和温度控制的结合，我们将能够启动、停止和直接磁荷动态。这些系统还可以为相变临界动力学研究提供新的实验模型，因为它们可以由众所周知的完全可溶的Ising系统建模，并为信息处理体系结构提供新的范例。

项目成果

Nonreciprocal spin-wave channeling along textures driven by the Dzyaloshinskii-Moriya interaction

• DOI: 10.1103/physrevb.89.224408
• 发表时间: 2014-06-13
• 期刊: PHYSICAL REVIEW B
• 影响因子: 3.7
• 作者: Garcia-Sanchez, Felipe;Borys, Pablo;Stamps, Robert L.
• 通讯作者: Stamps, Robert L.

Anisotropy engineering using exchange bias on antidot templates

使用抗点模板上的交换偏差进行各向异性工程

• DOI: 10.1063/1.4922055
• 发表时间: 2015
• 期刊: AIP Advances
• 影响因子: 1.6
• 作者: Goncalves F

Is the angular momentum of an electron conserved in a uniform magnetic field?

• DOI: 10.1103/physrevlett.113.240404
• 发表时间: 2014-12
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Colin R. Greenshields;R. Stamps;S. Franke-Arnold;S. Barnett

Reconfigurable wave band structure of an artificial square ice

• DOI: 10.1103/physrevb.93.134420
• 发表时间: 2016-04-18
• 期刊: PHYSICAL REVIEW B
• 影响因子: 3.7
• 作者: Iacocca, Ezio;Gliga, Sebastian;Heinonen, Olle
• 通讯作者: Heinonen, Olle

Exchange-dominated eigenmodes in sub-100 nm permalloy dots: A micromagnetic study at finite temperature

亚 100 nm 坡莫合金点中交换主导的本征模：有限温度下的微磁研究

• DOI: 10.1063/1.4862844
• 发表时间: 2014
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: Carlotti G