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

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering


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.

Planned Impact

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.


10 25 50
Description Racetrack memory devices represent an exciting new form of solid-state memory technology. This grant generated substantial insight into the underlying causes of stochastic (unreliable) behaviour in these systems. For example, we showed that the stochastic behaviours observed in racetrack devices can be understood as the result of the interplay between thermal excitations and the complex the high frequency magnetisation dynamics of the domain walls and the magnetisation history of the system. Building on this we showed how micromagnetic simulations of device behaviours could be used to qualitatively predict the stochastic behaviours of the system. We also demonstrated several possible ways in which these effects might be overcome: transporting DWs in 1D, geometrically defined propagating potential wells, and transforming stationary domain walls into "virtual" domain walls, where the magnetisation changes direction at a narrow break in the nanowire. Most excitingly our most recent modelling and experimental studies have demonstrated a materials science based solution to stochastic domain wall behaviours. In this approach Ni-Fe nanowires are doped with small amounts (~5%) of rare earth elements such as Terbium. This greatly simplifies their magnetisation dynamics and results in a dramatic suppression of stochastic behaviour.

Other studies stemming from the core studies of the grant have demonstrated a new kind of magnetic domain wall logic (chirality-based domain wall logic) that is likely to be more robust against the influence of stochastic behaviours than conventional domain wall logic. We have also shown how acoustic waves can be used to create a unable potential well for domain walls that could used to controllably transport them in low power memory devices.
Exploitation Route Thus far the impact of our studies is likely to be on informing our peers within academic circles, however we expect that as nanowire devices are developed further there is a chance of very real technological impact. In particular, we believe that the demonstration of a materials science-based solution to the problems of stochastic domain wall behaviour is likely to have a strong impact on future research and development in the field of magnetic domain wall devices and racetrack memory.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

Description While the main findings of our project i.e. a detailed understanding of the origin of stochastic effects in magnetic nanowire devices and approaches to mitigating their influence, have as yet been primarily of academic interest, the work has led to new projects involving industrial partners. For example, we have initiated new EPSRC and EU commission funded research projects, in partnership with ARM and IBM respectively, that aim to understand how stochastic effects can be utilised to realise neuromorphic computing technologies. We expect further industrial impact to emerge from these collaborations over the course of these projects.
First Year Of Impact 2019
Sector Other
Description From Stochasticity to Functionality: Probabilistic Computation with Magnetic Nanowires
Amount £755,424 (GBP)
Funding ID EP/S009647/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2019 
End 03/2022
Description Harnessing complexity: neuromorphic computation with magnetic domain walls
Amount £145,056 (GBP)
Funding ID RPG-2019-097 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2019 
End 08/2021
Description MARCH: Magnetic Architectures for Reservoir Computing Hardware
Amount £1,162,094 (GBP)
Funding ID EP/V006029/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2021 
End 06/2024
Description Research Grants
Amount £9,960 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2015 
End 03/2016
Description Royce Materials Challenge Accelerator Programme - Magnets that Think and Feel
Amount £56,023 (GBP)
Funding ID MCAP016 
Organisation Henry Royce Institute 
Sector Academic/University
Country United Kingdom
Start 11/2022 
End 04/2023
Description Collaboration with Dr Joe Friedman (University of Texas, Dallas) 
Organisation University of Texas
Country United States 
Sector Academic/University 
PI Contribution We have been investigating how magnetic nanowire devices can be natively used to realise data operations required to perform inference tasks.
Collaborator Contribution Dr Friedman has provided us support in understanding how nanomagnetic hardware could be used for creating devices that can perform inference tasks in hardware.
Impact So far the collaboration has not resulted in any outcomes, although we anticipate at least one paper and a grant application will result from it.
Start Year 2019
Description Collaboration with Prof Peter Fischer and Dr Mi-Young Im at the Advanced Light Source 
Organisation Lawrence Berkeley National Laboratory
Country United States 
Sector Public 
PI Contribution Performing magnetic imaging measurements at beamline 6.1.2 of the Advanced Light Source
Collaborator Contribution Providing access to the beamline and support during measurements.
Impact Two publications in Journal of Applied Physics (J. Appl. Phys. 114, 163901 (2013), J. Appl. Phys. 116, 123914 (2014)). One publication in Applied Physics Letters (Appl. Phys. Lett. 107, 222403 (2015)). Presentation at INTERMAG 2014, Dresden. Presentation at MMM/INTERMAG 2016, San Diego. Invited seminar at Department of Physics, University of Nottingham (2014).
Start Year 2012
Description Collaboration with University Groninigen on optically-induced magnetoacoustic interactions 
Organisation University of Groningen
Department Faculty of Science and Engineering
Country Netherlands 
Sector Academic/University 
PI Contribution My research group fabricated arrays of Ni nanowires on glass substrates for the group of Dr Ron Tobey. The samples were used to investigate how optically-induced surface acoustic waves could be coupled to the nanowires magnetisation dynamics. We have also performed micromagnetic simulations to allow understanding of the spin wave mode distributions within the nanowires, and show how these modes can be selectively excited by acoustic waves that are resonant with their frequencies.
Collaborator Contribution The group of Dr Ron Tobey characterised the Ni nanowires arrays using a time resolved magneto-optical spectroscopy system and analysed the experimental results.
Impact No outputs as yet. A paper on the work is currently under preparation and will be submitted in 2018. A poster describing the work will be presented at Magnetism 2018, Manchester.
Start Year 2018
Description Collaboration with University of Bath for performing scanning hall-probe microscopy measurements 
Organisation University of Bath
Country United Kingdom 
Sector Academic/University 
PI Contribution Preparing samples and developing control software for performing time and temperature scanning hall probe measurements of magnetic nanostructures.
Collaborator Contribution Performing scanning hall-probe measurements.
Impact No outputs yet.
Start Year 2012
Description Collaboration with University of Nottingham 
Organisation University of Nottingham
Country United Kingdom 
Sector Academic/University 
PI Contribution Measurement of multiferroic nanowire samples using focused MOKE magnetometry. Simulations of domain wall dynamics in the multiferroic nanowires. Measurement of NiFe nanowires doped with rare earth materials.
Collaborator Contribution Fabrication of multiferroic nanowire samples and analysis of experimental data.
Impact Presentation of results at 59th Annual Magnetism and Magnetic Materials Conference, Honolulu. Publication of paper in Physical Review Applied.
Start Year 2015
Description Collaboration with University of York 
Organisation University of York
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution Performing focused magneto-optic Kerr effect measurements of domain wall pinning due to exchange bias effects in planar magnetic nanowires. Assistance with analysis of data.
Collaborator Contribution Fabrication of devices for measurement. Analysis of data.
Impact One publication in Applied Physics Letters (Appl. Phys. Lett. 105, 162406 (2014))
Start Year 2013
Description University of Leeds - Surface Acoustic Waves 
Organisation University of Leeds
Department School of Electronic and Electrical Engineering Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution We performed to understand of the effects of surface acoustic waves (SAWs) on domain walls in artificial multi-ferroic systems. Our simulations showed that DWs could be both pinned and propagated using the SAWs.
Collaborator Contribution Prof. John Cunningham helped us calculate the stress profiles created by surface acoustic waves as the propagate through Lithium Niobate substrates, which we then implemented into our simulations.
Impact One publication in Applied Physics Letters (Appl. Phys. Lett. 107, 142405 (2015)) Presentation at MMM/Intermag 2016, San Diego. Invited presentation at York-Tohuku-Kaiserslautern research symposium 2015. Invited presentation at University of Leeds (2015)
Start Year 2013
Description Blog article on J. Phys+ 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact A short blog article was written on giving a layman's summary of a research paper investigating the stochastic behaviours of domain walls in ferromagnetic nanowires. The article was written to assist no-expert readers understand the importance of the work undertaken during my fellowship.
Year(s) Of Engagement Activity 2017
Description Presentation at Winter School 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Presentation "An introduction to micromagnetic modelling" at the Institute of Physics Magnetism winter school at the University of York. The presentation introduced first year PhD students to concepts and techniques associated with modelling magnetic materials at sub-micron length scales.
Year(s) Of Engagement Activity 2015,2016
Description Publication of an article on "The Conversation" 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact An article describing our recent results on surface acoustic wave-induced domain wall motion was publish on the website the conversation. The article was syndicated by several major technology news outlets (including Gizmodo) and was read in excess of 35,000 times. A number of journalists writing for embedded computing magazines also wrote articles about our work.
Year(s) Of Engagement Activity 2015