MAGNETISM YOU CAN RELY ON: Understanding Stochastic Behaviour in Nanomagnetic Devices.

在过去的20年里，磁性技术最大的进步是发展了“纳米磁性”装置，即尺寸小到十亿分之一米的磁性系统。最常见的例子是计算机硬盘驱动器，其中用于读回数据的存储介质和传感器本质上都是纳米磁性的。现代个人电脑的普及意味着英国的绝大多数家庭和企业，实际上在许多发达国家，现在在某种程度上依赖于纳米磁性技术。许多其他纳米磁性设备也在开发中，包括磁存储设备、磁逻辑设备、微波谐振器、医疗诊断设备和磁性传感器。这些新技术有可能比现有的同类技术更快、更便宜、更高效。例如，非易失性磁存储芯片将允许个人计算机启动到关机前的确切状态，从而消除了长时间保持系统开机的必要性。同样，磁性生物芯片很快将允许在医生的外科手术而不是在实验室进行复杂的医学测试，而且价格很低。在纳米磁系统中，理解有限温度的影响至关重要，因为热效应会引入无序，使人无法准确预测设备的行为。在硬盘中，热刺激可以通过颠倒组成文件的各个“位”来导致数据丢失。这一现象是制约现代硬盘容量的主要因素。在其他技术中，热扰动的随机化效应使得无法预测设备在执行外部操作之前和之后将处于的确切状态，从而使设备变得不可靠。同样，这种可靠性的缺乏是阻止新的纳米磁性技术以及它们将带来的社会和环境效益在商业街上获得的主要因素。尽管这些“随机”效应具有巨大的技术重要性，但人们对它们的理解很少，大多数研究只从现象学或经验的方式来考虑它们。为了能够理解和准确预测磁系统中的随机行为，有必要对两个参数有一个透彻的了解：能垒，它决定了系统被限制在给定状态的强度；以及尝试频率，它决定了热刺激试图改变系统配置的频率。不幸的是，这两个参数都不能通过标准测量技术获得，因此它们既不能很好地理解，也不能很好地描述。在这个联谊会中，我将使用时间、频率和温度分辨测量，结合新的数值建模技术，直接测量广泛的技术相关磁系统的尝试频率和能垒。这些将包括用于新硬盘技术、存储设备、信息处理系统、新型传感器和微波谐振器的那些。在这样做的过程中，我将创建第一个全面的框架，用来a)理解、b)预测和c)减轻纳米磁性设备中随机行为的影响。这将使研究人员和技术人员最终能够定量预测热扰动将如何影响纳米磁性设备，并了解如何克服它们带来的问题。目前，学术界和工业界对开发新的纳米磁性技术的兴趣激增。这种奖学金对于确保进步不会因为缺乏对随机磁性行为的理解而受到阻碍，并确保纳米磁性技术的巨大潜力被带到商业街上来，将是至关重要的。

The greatest advance in magnetic technology in the last 20 years has been the development of "nanomagnetic" devices, magnetic systems with dimensions as small as ten billionths of a metre. The most common examples of this are found in computer hard-disk drives, where both the storage media and the sensors used to read data back are nanomagnetic in nature. The prevalence of modern personal computers means that the vast majority of homes and businesses in the United Kingdom, and indeed in much of the developed world, are now in some way dependent on nanomagnetic technology. Many other nanomagnetic devices are also being developed including magnetic memory devices, magnetic logic devices, microwave resonators, devices for medical diagnostics and magnetic sensors. These new technologies have the potential to be faster, cheaper and more efficient than their existing counterparts. For example, non-volatile magnetic memory chips will allow personal computers to be booted up into the exact state they were in prior to being shut down, removing the necessity of leaving systems switched on over extended periods. Similarly, magnetic bio-chips will soon allow complex medical tests to be performed at the doctor's surgery rather than in a laboratory, and at a faction of the price.In nanomagnetic systems understanding the effect of finite temperature is of critical importance, as thermal effects introduce disorder making it impossible to predict exactly how a device will behave. In hard-disks thermal excitations can cause data to be lost by reversing the individual "bits" that make up a file. This phenomenon is the primary factor that restricts the capacity of modern hard-disks. In other technologies the randomising effects of thermal perturbations make devices unreliable by making it impossible to predict the exact state a device will be in before and after an external operation is performed. Again, this lack of reliability is a leading factor in preventing new nanomagnetic technologies, and the social and environmental benefits they will bring, being available on the high street.Despite the huge technological importance of these "stochastic" effects they are poorly understood with most studies considering them only in a phenomenological or empirical fashion. To be able to understand and accurately predict stochastic behaviour in magnetic systems it is necessary to have a thorough knowledge of two parameters: the energy barrier, which determines how strongly a system is confined to a given state; and the attempt frequency, which determines how often thermal excitations try to alter the configuration of a system. Unfortunately neither of these parameters are accessible by standard measurement techniques, and hence they are neither well understood, nor characterised.In this fellowship I will use time, frequency and temperature resolved measurements, coupled with new numerical modelling techniques, to directly measure both attempt frequencies and energy barriers across a broad range of technologically relevant magnetic systems. These will include those for use in new hard-disk technologies, memory devices, information processing systems, novel sensors and microwave resonators. In doing this I will create the first comprehensive framework with which to a) understand, b) predict and c) mitigate the effects of stochastic behaviour in nanomagnetic devices. This will allow researchers and technologists to, at last, quantitatively predict how thermal perturbations will affect nanomagnetic devices, and understand how the problems they introduce can be overcome.There is currently an explosion of interest in developing new nanomagnetic technologies in both academia and in industry. This fellowship will be critical to ensuring that progress is not inhibited by a lack of understanding of stochastic magnetic behaviour, and that the great potential of nanomagnetic technology is brought to the high street.