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

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.

Stochastic effects in magnetic materials and devices are of great technological importance. For example, the key concern in the design of contemporary hard-disk drives is avoiding data being lost through their randomising influence. These technical difficulties will become more acute in the development of the next generation of hard-disk drives, which will be based on nano-structured "bit-patterned" media. A transition to these new forms of storage technology is vital to the current data storage roadmap.

My fellowship will be critical to the development of bit-patterned media, as it will allow a deeper and more quantitative understanding of stochastic effects such systems. I will also develop methods by which the detrimental effects of stochastic behaviour on device performance may be mitigated. This will ultimately offer industry new routes through which to tackle engineering challenges. Additionally, the Fellowship will thoroughly assess both experimental and theoretical techniques for quantitatively measuring and predicting the parameters that underlie stochastic behaviour. These techniques will offer valuable design tools for industry. Considering all of the above, the data storage industry is expected to greatly benefit from my research. This industry includes internationally important companies such as Hitachi, Samsung, Western Digital and Seagate.

The fellowship will also explore soft-ferromagnetic systems for which device applications are at an earlier stage of development. Applications here include non-volatile memory devices, magnetic logic systems, tools for medical diagnostics, magnetic sensors and resonators for wireless communications. Many of these technologies have yet to move beyond simple prototypes, largely due to problems with achieving reliable magnetic behaviour. Again, this fellowship will address these issues in a quantitative manner, and in doing so lead to the successful realisation of new devices, the development of which is currently frustrated. Companies with significant research interests in developing these new forms of nanomagnetic devices include IBM, NEC, Toshiba, Freescale Semiconductor and NVE Corporation.

A fundamental understanding of stochastic effects is also valuable for technologists investigating systems that will not be directly studied in this fellowship. For example, a major factor effect the performance of hybrid cars is the thermal demagnetisation of permanent magnets. The underlying phenomena in these processes are ultimately the same as those I will investigate.

In the medium-to-long term (5-15 years) the main benefit economic benefit of the fellowship will be its influence on bringing new nanomagnetic technologies to the high-street. The first of these technologies to be realised will be hard-disks based on bit-patterned media, while the more novel technologies may take longer. The improved capacity, speed and efficiency of these new nanomagnetic devices will be of great benefit to society. For example, the development of non-volatile memory devices will greatly improve the energy efficiency of computing technologies, and will have a subsequent environmental impact, while new tools for medical diagnostics will allow rapid, point-of-care screening for a wide range of diseases and genetic disorders. The development of higher density hard-disks is also likely to become increasingly important as the use of high-definition audio-visual content becomes more commonplace.

The proposed project requires a large range of contemporarily relevant research techniques and thus will provide PhD students with an extensive portfolio of skills for their future careers. Overall, the training which will be provided through the project will equip students with skills that will be extremely useful for science and engineering based careers either in academia or in the private sector. A good supply of graduates with such skills is key to the future success of the UK economy.