Frustration: more ways to emergent behaviour.

功能性磁性在技术应用中不断被开发。磁性现象最初用于指南针，而磁性特性仍在开发中，以帮助在硬盘驱动器上存储数字数据。事实上，2013年硬盘行业预计将产生330亿美元的销售额，这一点很重要，因为更多的信息是以数字方式存储的，位密度需要继续增加。需要开发新的磁性数据存储方法，需要可以直接输入到工业中的基础研究。一种这样的研究途径是磁力受挫，即一个系统内的两两相互作用不能同时得到满足。如果这些受挫的相互作用发生在三角形晶格(1纳米大小)的交叉点上，那么净矩可以用作具有难以置信比特密度的比特。事实上，目前正在开发人工受挫系统(比晶格大3个数量级)来测试这种存储数据的想法。然而，为了操纵这项技术，仍然需要了解纳米级的基本物理过程。对低温受挫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然带来曲折和惊喜。具体地说，由于紧急行为的概念，磁性最近引起了人们的兴奋。这本质上是对意想不到的特性的描述，这些特性从根本上挑战了如何理解和操纵日常生活中的磁性。在被称为自旋冰的受挫物质中(之所以叫自旋冰，是因为最低能量的基态有16种不同的自旋组态，质子组态的数量与水冰相同)，已经发现了浮现的磁单极子。这些单极子的作用类似于电荷，因为它们可以被磁场驱离，就像电被电场控制一样。然而，为了理解这些性质，自旋冰的样本需要在非常低的温度下测量，远远低于1K，因为产生单极的激发具有热激活行为，具有大约4K的能隙。因此，为了在稀释限内使电荷能够被操纵，磁化必须用低温(&lt；500MK)稀释冰箱来测量。一个需要回答的问题是，如何通过控制实验参数(如冷却速度)来控制“磁化率”。掌握这些特性的一个方法是测量磁化强度。具体地说，样品需要多长时间才能对可用于测量自旋冰动力学的外加磁场做出响应。因为单极子的产生取决于自旋冰通过磁性冰冻温度冷却的速度，所以了解随后的动力学反应是很重要的。这使得能够操纵单极密度和随后的动力学。此外，目前的动力学需要在广泛的动态范围内进行研究，并将建造一台仪器来测量频率高达1 MHz的磁化率的变化。将开发的仪器将在英国独一无二，也是全球极少数仪器之一，它还将允许研究磁性材料的量子属性。由于热涨落会淹没量子激发，因此需要较低的温度。预计量子自旋液体磁体中会出现新的行为，这种磁体包含紧密堆积的磁离子，但相互作用受挫。也可以用磁力计测量孤立磁性离子的量子行为。这允许操纵不同的能级并理解基本性质。

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.