权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Frustration: more ways to emergent behaviour.

挫折：更多的紧急行为方式。

基本信息

批准号：
EP/L019760/1
负责人：
Sean Richard Giblin
金额：
$ 11.41万
依托单位：
CARDIFF UNIVERSITY
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%2FL019760%2F1
关键词：
Frustration more ways emergent behaviour.

项目摘要

Functional magnetic properties are constantly exploited in technological applications. The phenomena of magnetism was originally used in a compass and magnetic properties are still being developed to help store digital data on hard drives. Indeed the hard drive industry in 2013 is expected to generate $33 billion of sales, importantly as more information is stored digitally the bit density needs to carry on increasing. Novel methods of magnetic data storage need to be developed, requiring fundamental research which can be fed directly into industry. One such avenue of research is magnetic frustration, where pairwise interactions within a system cannot be simultaneously satisfied. If these frustrated interactions occur on the intersections of a triangular crystal lattice (1 nanometre in size) the net moment can be used as a bit with an incredible bit density. Indeed artificial frustrated systems (3 orders of magnitude bigger than the crystal lattice) are currently being developed to test this idea of storing data. However the fundamental physical processes on the nanometre scale still need to be understood in order to manipulate this technology. Fundamental investigations of frustrated systems at low temperature will redefine how we understand magnetic materials, and how we store and manipulate information in the future.Fundamental properties of magnetic systems are still delivering twists and surprises. Specifically, magnetism has recently generated excitement because of the concept of emergent behaviour. This is essentially a description of unexpected properties that fundamentally challenge how to understand and manipulate magnetism on an every day basis. In the frustrated material know as spin ice (so called because the lowest energy ground state has 16 different spin configurations, the same number of proton configurations as water ice) emergent magnetic monopoles have been discovered. These monopoles act like electric charges in that they can be driven apart by a magnetic field, in much the same way electricity is controlled by electric fields. However to understand these properties the sample of spin ice needs to be measured at very low temperatures, much less than 1 K as the excitation which creates monopoles has a thermally activated behaviour with an energy gap around 4 K. Therefore to be in the dilute limit to enable charges to be manipulated the magnetisation has to be measured with a low temperature (< 500 mK) dilution fridge. One question to be to answered is how 'magnetricity' can be manipulated by controlling experimental parameters, such as cooling rate.One way to get a handle on the properties is to measure the magnetization. Specifically how long does the sample take to respond to an applied field which can be used as a measurement of spin ice dynamics. Because the creation of monopoles depends on how quickly spin ice is cooled through the magnetic freezing temperature it is important to understand how the dynamics respond afterwards. This enables the manipulation of the monopole density and the subsequent dynamics. Moreover the dynamics present need to be investigated over a wide dynamical regime and an instrument will be built to measure the changes in the susceptibility at frequencies up to 1MHz.The instrument that will be developed, which will be unique in the UK and one of very few worldwide, will also allow the study of quantum properties in magnetic materials. The low temperature is required as thermal fluctuations will swamp the quantum excitations. Emergent behaviour is expected in quantum spin liquid magnets which contain tightly packed magnetic ions with frustrated interactions. Quantum behaviour can also be measured in lone magnetic ions with magnetometers. This allows the manipulation of different energy levels and understanding of the fundamental properties.

功能磁性在技术应用中不断被开发。磁现象最初用于指南针，磁特性仍在开发中，以帮助在硬盘上存储数字数据。事实上，2013年硬盘行业预计将产生330亿美元的销售额，重要的是，随着更多的信息以数字方式存储，位密度需要继续增加。需要开发新的磁数据存储方法，这需要可以直接投入工业的基础研究。其中一个这样的研究途径是磁挫折，其中一个系统内的成对相互作用不能同时满足。如果这些受抑的相互作用发生在三角形晶格（1纳米大小）的交叉点上，则净矩可以用作具有令人难以置信的位密度的位。事实上，人工受抑系统（比晶格大3个数量级）目前正在开发中，以测试这种存储数据的想法。然而，纳米尺度上的基本物理过程仍然需要理解，以便操纵这项技术。对低温下受抑系统的基础研究将重新定义我们对磁性材料的理解，以及我们未来如何存储和处理信息。磁性系统的基本性质仍在带来曲折和惊喜。具体来说，最近由于涌现行为的概念，磁力引起了人们的兴奋。这本质上是对意想不到的性质的描述，这些性质从根本上挑战了如何理解和操纵每天的磁性。在被称为自旋冰的受抑材料中（之所以这么叫是因为最低能量基态有16种不同的自旋构型，与水冰的质子构型相同），人们发现了涌现的磁单极子。这些磁单极子的行为就像电荷一样，因为它们可以被磁场分开，就像电场控制电一样。然而，为了理解这些性质，自旋冰的样品需要在非常低的温度下测量，远低于1 K，因为产生单极子的激发具有热激活行为，能隙约为4 K。因此，为了在稀释极限中使电荷能够被操纵，必须用低温（< 500 mK）稀释冰箱测量磁化强度。一个有待回答的问题是如何通过控制实验参数（如冷却速度）来操纵“磁性”。掌握这些性质的一种方法是测量磁化强度。具体地说，样品需要多长时间才能对施加的场作出响应，这可以用作自旋冰动力学的测量。由于磁单极子的产生取决于自旋冰在磁冻结温度下冷却的速度，因此了解随后的动力学响应是很重要的。这使得能够操纵电子束密度和随后的动态。此外，目前的动力学需要在广泛的动力学领域进行研究，并将建立一种仪器来测量频率高达1MHz的磁化率变化。将开发的仪器在英国是独一无二的，也是世界上为数不多的仪器之一，也将允许研究磁性材料的量子特性。低温是必需的，因为热涨落会淹没量子激发。在量子自旋液体磁体中，包含紧密堆积的磁性离子，相互作用受阻，预计会出现紧急行为。量子行为也可以用磁强计在孤磁离子中测量。这允许操纵不同的能量水平和理解的基本属性。