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

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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.