A novel method for the injection and manipulation of magnetic charge states in nanostructures

Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360 degree domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method's efficacy via the injection and spatial manipulation of 360 degree domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.Comment: in Scientific Reports (2016

Effective pinning energy landscape perturbations for propagating magnetic domain walls

The interaction between a magnetic domain wall and a pinning site is explored in a planar nanowire using micromagnetics to reveal perturbations of the pinning energetics for propagating domain walls. Numerical simulations in the high damping ’quasi-static’ and low damping ’dynamic’ regimes are compared and show clear differences in de-pinning fields, indicating that dynamical micromagnetic models, which incorporate precessionally limited magnetization processes, are needed to understand domain wall pinning. Differences in the micromagnetic domain wall structure strongly influence the pinning and show periodic behaviour with increasing applied field associated with Walker breakdown. In the propagating regime pinning is complicated

Suppression of Walker breakdown in magnetic domain wall propagation through structural control of spin wave emission

The control of individual magnetic domain walls has potential for future spintronic memory and data processing applications. The speed and reliability of such devices are determined by the dynamic properties of the domain walls. Typically, spin precession limitations lead to Walker breakdown, limiting wall velocity resulting in low mobility. Here, we show the suppression of Walker breakdown by the careful design of small amplitude periodic nanowire structuring to match the periodicity of domain wall spin structure transformations. This opens up a channel for energy dissipation via spin wave emission, allowing a domain wall to maintain its spin structure during propagation

Olfactory variation in mouse husbandry and its implications for refinement and standardisation: UK survey of non-animal scents

With their highly sensitive olfactory system, the behaviour and physiology of mice are not only influenced by the scents of conspecifics and other species, but also by many other chemicals in the environment. The constraints of laboratory housing limit a mouse’s capacity to avoid aversive odours that could be present in the environment. Potentially odorous items routinely used for husbandry procedures, such as sanitizing products and gloves, could be perceived by mice as aversive or attractive, and affect their behaviour, physiology and experimental results. A survey was sent to research institutions in the UK to enquire about husbandry practices that could impact on the olfactory environment of the mouse. Responses were obtained from 80 individuals working in 51 institutions. Husbandry practices varied considerably. Seventy percent of respondents reported always wearing gloves for handling mice, with nitrile being the most common glove material (94%) followed by latex (23%) and vinyl (14%). Over six different products were listed for cleaning surfaces, floors, anaesthesia and euthanasia chambers and behavioural apparatus. In all cases Trigene™ (now called Anistel™) was the most common cleaning product used (43, 41, 40 and 49%, respectively). Depending on the attribute considered, between 7 and 19% of respondents thought that cleaning products definitely, or were likely to, have strong effects on standardization, mouse health, physiology or behaviour. Understanding whether and how these odours affect mouse welfare will help to refine mouse husbandry and experimental procedures through practical recommendations, to improve the quality of life of laboratory animals and the experimental data obtained

Changes in the population and community structure of corals during recent disturbances (February 2016-October 2017) on Maldivian coral reefs

Climate change is the greatest threat to coral reef ecosystems. In particular, increasing ocean temperatures are causing severe and widespread coral bleaching, contributing to extensive coral loss and degradation of coral reef habitats globally. Effects of coral bleaching are not however, equally apportioned among different corals, leading to shifts in population and community structure. This study explored variation in bleaching susceptibility and mortality associated with the 2016 severe mass bleaching in the Central Maldives Archipelago. Five dominant coral taxa (tabular Acropora, Acropora humilis, Acropora muricata, Pocillopora and massive Porites) were surveyed in February 2016 and October 2017 to test for changes in abundance and size structure. Substantial taxonomic differences in rates of mortality were observed; the most severely affected taxa, Acropora, were virtually extirpated during the course of this study, whereas some other taxa (most notably, massive Porites) were relatively unaffected. However, even the least affected corals exhibited marked changes in population structure. In February 2016 (prior to recent mass-bleaching), size-frequency distributions of all coral taxa were dominated by larger size classes with over-centralized, peaked distributions (negatively skewed with positive kurtosis) reflecting a mature population structure. In October 2017, after the bleaching, coral populations were dominated by smaller and medium size classes, reflecting high levels of mortality and injury among larger coral colonies. Pronounced changes in coral populations and communities in the Maldives, caused by coral bleaching and other disturbances (outbreaks of crown-of-thorns starfish and sedimentation), will constrain recovery capacity, further compounding upon recent coral loss

Focused-ion-beam induced interfacial intermixing of magnetic bilayers for nanoscale control of magnetic properties

Modification of the magnetic properties in a thin-film ferromagnetic/non-magnetic bilayer system by low-dose focused ion-beam (FIB) induced intermixing is demonstrated. The highly localized capability of FIB may be used to locally control magnetic behaviour at the nanoscale. The magnetic, electronic and structural properties of NiFe/Au bilayers were investigated as a function of the interfacial structure that was actively modified using focused Ga+ ion irradiation. Experimental work used MOKE, SQUID, XMCD as well as magnetoresistance measurements to determine the magnetic behavior and grazing incidence x-ray reflectivity to elucidate the interfacial structure. Interfacial intermixing, induced by low-dose irradiation, is shown to lead to complex changes in the magnetic behavior that are associated with monotonic structural evolution of the interface. This behavior may be explained by changes in the local atomic environment within the interface region resulting in a combination of processes including the loss of moment on Ni and Fe, an induced moment on Au and modifications to the spin-orbit coupling between Au and NiFe

Magnetization switching and domain-wall propagation behavior in edge-modulated ferromagnetic nanowire structures

The magnetization reversal processes in ferromagnetic nanowires with sinusoidally modulated edges were investigated as a function of modulation amplitude and wavelength. The reversal processes were studied in two regimes: nucleation controlled reversal and magnetization reversal mediated by domain-wall propagation. In the latter case, domain walls were introduced using both nucleation-pad structures and local pulsed-field injection techniques. The reversal behavior shows that competing effects govern the switching fields in these structures, giving a minimum as a function of modulation wavelength, showing promising results for improved control of domain-wall propagation behavior. The experimental results were interpreted with detailed micromagnetic simulations and an analytical model, based on the demagnetization effects of the modulation upon the spin structure of the wire. The analysis highlights consistent trends in the reversal behavior resulting from modulation, and, significantly, the switching behavior is found to be scalable in relation to the amplitude and wavelength

Embarking on a research project…or research for the absolute novice

Peer reviewedPublisher PD

Can self-affirmation exacerbate adverse reactions to stress under certain conditions?

OBJECTIVE: Self-affirmation has repeatedly been shown to reduce adverse psychological and physiological responses to stress. However, it is plausible that self-affirmation could exacerbate negative reactions to stress under certain conditions. The current research explored whether self-affirmation would increase negative psychological responses to a stressor occurring in a central life domain characterised by low levels of control. DESIGN: Female participants (Study 1 N = 132; Study 2 N = 141) completed baseline measures of anxiety and mood. They were then randomly allocated to complete a self-affirmation or control task, before reading a narrative documenting a stressful birth and imagining themselves in the place of the woman giving birth. After completing this task, participants again reported their levels of anxiety and positive mood. MAIN OUTCOME MEASURES: Anxiety and positive mood assessed at follow-up. RESULTS: Study 1 demonstrated that self-affirmed women experienced increased anxiety and less positive mood at follow-up, compared both to baseline and to women in the control condition. Study 2 revealed that the effect of self-affirmation on outcomes was moderated by fear of childbirth. CONCLUSION: These results provide preliminary evidence that self-affirmation may worsen negative responses to stressors under certain conditions and for certain individuals