92 results found
Gartside JC, Stenning KD, Vanstone A, et al., 2022, Reconfigurable Training and Reservoir Computing in an Artificial Spin-Vortex Ice via Spin-Wave Fingerprinting, Nature Nanotechnology, Vol: 17, Pages: 460-469
Strongly-interacting artificial spin systems are moving beyond mimickingnaturally-occurring materials to emerge as versatile functional platforms, fromreconfigurable magnonics to neuromorphic computing. Typically artificial spinsystems comprise nanomagnets with a single magnetisation texture: collinearmacrospins or chiral vortices. By tuning nanoarray dimensions we achievemacrospin/vortex bistability and demonstrate a four-state metamaterialspin-system 'Artificial Spin-Vortex Ice' (ASVI). ASVI can host Ising-likemacrospins with strong ice-like vertex interactions, and weakly-coupledvortices with low stray dipolar-field. Vortices and macrospins exhibitstarkly-differing spin-wave spectra with analogue-style mode-amplitude controland mode-frequency shifts of df = 3.8 GHz. The enhanced bi-textural microstate space gives rise to emergent physicalmemory phenomena, with ratchet-like vortex training and history-dependentnonlinear fading memory when driven through global field cycles. We employspin-wave microstate fingerprinting for rapid, scaleable readout of vortex andmacrospin populations and leverage this for spin-wave reservoir computation.ASVI performs linear and non-linear mapping transformations of diverse inputsignals as well as chaotic time-series forecasting. Energy costs of machinelearning are spiralling unsustainably, developing low-energy neuromorphiccomputation hardware such as ASVI is crucial to achieving a zero-carboncomputational future.
Vanstone A, Gartside JC, Stenning KD, et al., 2022, Spectral-fingerprinting: microstate readout via remanence ferromagnetic resonance in artificial spin systems, New Journal of Physics, Vol: 24, ISSN: 1367-2630
Artificial spin ices (ASIs) are magnetic metamaterials comprising geometrically tiled strongly-interacting nanomagnets. There is significant interest in these systems spanning the fundamental physics of many-body systems to potential applications in neuromorphic computation, logic, and recently reconfigurable magnonics. Magnonics focused studies on ASI have to date have focused on the in-field GHz spin-wave response, convoluting effects from applied field, nanofabrication imperfections ('quenched disorder') and microstate-dependent dipolar field landscapes. Here, we investigate zero-field measurements of the spin-wave response and demonstrate its ability to provide a 'spectral fingerprint' of the system microstate. Removing applied field allows deconvolution of distinct contributions to reversal dynamics from the spin-wave spectra, directly measuring dipolar field strength and quenched disorder as well as net magnetisation. We demonstrate the efficacy and sensitivity of this approach by measuring ASI in three microstates with identical (zero) magnetisation, indistinguishable via magnetometry. The zero-field spin-wave response provides distinct spectral fingerprints of each state, allowing rapid, scaleable microstate readout. As artificial spin systems progress toward device implementation, zero-field functionality is crucial to minimize the power consumption associated with electromagnets. Several proposed hardware neuromorphic computation schemes hinge on leveraging dynamic measurement of ASI microstates to perform computation for which spectral fingerprinting provides a potential solution.
Dion T, Gartside JC, Vanstone A, et al., 2021, Observation and control of collective spin-wave mode-hybridisation in chevron arrays and square, staircase and brickwork artificial spin ices, Physical Review Research, Vol: 4, Pages: 1-9, ISSN: 2643-1564
Dipolar magnon-magnon coupling has long been predicted in nano-patternedartificial spin systems. However, observation of such phenomena and relatedcollective spin-wave signatures have until recently proved elusive or limitedto low-power edge-modes which are difficult to measure experimentally. Here wedescribe the requisite conditions for dipolar mode-hybridisation, how it may becontrolled, why it was not observed earlier and how strong coupling may occurbetween nanomagnet bulk-modes. We experimentally investigate fournano-patterned artificial spin system geometries: `chevron' arrays, `square',`staircase' and `brickwork' artificial spin ices. We observe significantdynamic dipolar-coupling in all systems with relative coupling strengths andavoided-crossing gaps supported by micromagnetic-simulation results. Wedemonstrate reconfigurable mode-hybridisation regimes in each system viamicrostate control, and in doing so elucidate the underlying dynamics governingdynamic dipolar-coupling with implications across reconfigurable magnonics. Wedemonstrate that confinement of the bulk-modes via edge effects play a criticalrole in dipolar hybridised-modes, and treating nanoislands as a coherentlyprecessing macro-spins or standing spin-waves are insufficient to captureexperimentally-observed coupling phenomena. Finally, we present aparameter-space search detailing how coupling strength may be tuned viananofabrication-dimensions and material properties.
Chaurasiya AK, Mondal AK, Gartside JC, et al., 2021, Comparison of spin-wave modes in connected and disconnected artificial spin ice nanostructures using Brillouin light scattering spectroscopy, ACS Nano, Vol: 15, Pages: 11734-11742, ISSN: 1936-0851
Artificial spin ice systems have seen burgeoning interest due to their intriguing physics and potential applications in reprogrammable memory, logic, and magnonics. Integration of artificial spin ice with functional magnonics is a relatively recent research direction, with a host of promising results. As the field progresses, direct in-depth comparisons of distinct artificial spin systems are crucial to advancing the field. While studies have investigated the effects of different lattice geometries, little comparison exists between systems comprising continuously connected nanostructures, where spin-waves propagate via dipole-exchange interaction, and systems with nanobars disconnected at vertices, where spin-wave propagation occurs via stray dipolar field. Gaining understanding of how these very different coupling methods affect both spin-wave dynamics and magnetic reversal is key for the field to progress and provides crucial system-design information including for future systems containing combinations of connected and disconnected elements. Here, we study the magnonic response of two kagome spin ices via Brillouin light scattering, a continuously connected system and a disconnected system with vertex gaps. We observe distinct high-frequency dynamics and magnetization reversal regimes between the systems, with key distinctions in spin-wave localization and mode quantization, microstate trajectory during reversal and internal field profiles. These observations are pertinent for the fundamental understanding of artificial spin systems and broader design and engineering of reconfigurable functional magnonic crystals.
Chaurasiya AK, Mondal AK, Gartside JC, et al., 2021, Comparison of Spin-Wave Modes in Connected and Disconnected Artificial Spin Ice Nanostructures Using Brillouin Light Scattering Spectroscopy, ACS Nano, Vol: 15, Pages: 11734-11734
Artificial spin ice systems have seen burgeoning interest due to theirintriguing physics and potential applications in reprogrammable memory, logicand magnonics. Integration of artificial spin ice with functional magnonics isa relatively recent research direction, with a host of promising results. Asthe field progresses, direct in-depth comparisons of distinct artificial spinsystems are crucial to advancing the field. While studies have investigated theeffects of different lattice geometries, little comparison exists betweensystems comprising continuously connected nanostructures, where spin-wavespropagate via dipole-exchange interaction, and systems with nanobarsdisconnected at vertices where spin-wave propagation occurs via straydipolar-field. Gaining understanding of how these very different couplingmethods affect both spin-wave dynamics and magnetic reversal is key for thefield to progress and provides crucial system-design information including forfuture systems containing combinations of connected and disconnected elements.Here, we study the magnonic response of two kagome spin ices via Brillouinlight scattering, a continuously connected system and a disconnected systemwith vertex gaps. We observe distinct high-frequency dynamics and magnetizationreversal regimes between the systems, with key distinctions in spin-wavelocalization and mode quantization, microstate-trajectory during reversal andinternal field-profiles. These observations are pertinent for the fundamentalunderstanding of artificial spin systems and broader design and engineering ofreconfigurable functional magnonic crystals.
Gartside JC, Vanstone A, Dion T, et al., 2021, Reconfigurable magnonic mode-hybridisation and spectral control in a bicomponent artificial spin ice, Nature Communications, Vol: 12, ISSN: 2041-1723
Strongly-interacting nanomagnetic arrays are finding increasing use as modelhost systems for reconfigurable magnonics. The strong inter-element couplingallows for stark spectral differences across a broad microstate space due toshifts in the dipolar field landscape. While these systems have yieldedimpressive initial results, developing rapid, scaleable means to access abroadrange of spectrally-distinct microstates is an open research problem.We presenta scheme whereby square artificial spin ice is modified by widening a'staircase' subset of bars relative to the rest of the array, allowingpreparation of any ordered vertex state via simple global-field protocols.Available microstates range from the system ground-state to high-energy'monopole' states, with rich and distinct microstate-specific magnon spectraobserved. Microstate-dependent mode-hybridisation and anticrossings areobserved at both remanence and in-field with dynamic coupling strength tunablevia microstate-selection. Experimental coupling strengths are found up to g /2$\pi$ = 0.15 GHz. Microstate control allows fine mode-frequency shifting, gapcreation and closing, and active mode number selection.
Stenning KD, Gartside JC, Dion T, et al., 2020, Magnonic bending, phase shifting and interferometry in a 2D reconfigurable nanodisk crystal., ACS Nano, Vol: 15, Pages: 674-685, ISSN: 1936-0851
Strongly interacting nanomagnetic systems are pivotal across next-generation technologies including reconfigurable magnonics and neuromorphic computation. Controlling magnetization states and local coupling between neighboring nanoelements allows vast reconfigurability and a host of associated functionalities. However, existing designs typically suffer from an inability to tailor interelement coupling post-fabrication and nanoelements restricted to a pair of Ising-like magnetization states. Here, we propose a class of reconfigurable magnonic crystals incorporating nanodisks as the functional element. Ferromagnetic nanodisks are crucially bistable in macrospin and vortex states, allowing interelement coupling to be selectively activated (macrospin) or deactivated (vortex). Through microstate engineering, we leverage the distinct coupling behaviors and magnonic band structures of bistable nanodisks to achieve reprogrammable magnonic waveguiding, bending, gating, and phase-shifting across a 2D network. The potential of nanodisk-based magnonics for wave-based computation is demonstrated via an all-magnon interferometer exhibiting XNOR logic functionality. Local microstate control is achieved here via topological magnetic writing using a magnetic force microscope tip.
Gartside JC, Jung SG, Yoo SY, et al., 2020, Current-controlled nanomagnetic writing for reconfigurable magnonic crystals, Communications Physics, Vol: 3, Pages: 1-1, ISSN: 2399-3650
Strongly-interacting nanomagnetic arrays are crucial across an ever-growing suite of technologies. Spanning neuromorphic computing, control over superconducting vortices and reconfigurable magnonics, the utility and appeal of these arrays lies in their vast range of distinct, stable magnetization states. Different states exhibit different functional behaviours, making precise, reconfigurable state control an essential cornerstone of such systems. However, few existing methodologies may reverse an arbitrary array element, and even fewer may do so under electrical control, vital for device integration. We demonstrate selective, reconfigurable magnetic reversal of ferromagnetic nanoislands via current-driven motion of a transverse domain wall in an adjacent nanowire. The reversal technique operates under all-electrical control with no reliance on external magnetic fields, rendering it highly suitable for device integration across a host of magnonic, spintronic and neuromorphic logic architectures. Here, the reversal technique is leveraged to realize two fully solid-state reconfigurable magnonic crystals, offering magnonic gating, filtering, transistor-like switching and peak-shifting without reliance on global magnetic fields.
Arroo DM, Gartside JC, Branford WR, 2019, Sculpting the spin-wave response of artificial spin ice via microstate selection, Physical Review B: Condensed Matter and Materials Physics, Vol: 100, Pages: 1-7, ISSN: 1098-0121
Artificial spin ice (ASI) systems have emerged as promising hosts for magnonic applications due to a correspondence between their magnetic configuration and spin dynamics. Though it has been demonstrated that spin-wave spectra are influenced by the ASI microstate the precise nature of this relationship has remained unclear. Recent advances in controlling the magnetic configuration of ASI make harnessing the interplay between spin dynamics and the microstate achievable. This could allow diverse applications including reconfigurable magnonic crystals and programmable microwave filters. However, extracting any novel functionality requires a full understanding of the underlying spin-wave/microstate interaction. Here, we present a systematic analysis of how the microstate of a honeycomb ASI system affects its spin-wave spectrum through micromagnetic simulations. We find the spectrum to be highly tunable via the magnetic microstate, allowing the (de)activation of spin-wave modes and band-gap tuning via magnetic reversal of individual nanoislands. Symmetries of ASI systems and the chirality of “monopole” defects are found to play important roles in determining the high-frequency magnetic response.
Cohen L, Boldrin D, Johnson F, et al., 2019, The biaxial strain dependence of magnetic order in spin frustrated mn3nin thin films, Advanced Functional Materials, Vol: 29, ISSN: 1616-301X
Multi-component magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetisation for energy efficient memory, data storage and cooling applications. Strong spin-lattice coupling extends this functionality further by allowing electric-field-control of magnetisation via strain coupling with a piezoelectric . Here we explore the magnetic phase diagram of piezomagnetic Mn3NiN thin films, with a frustrated non-collinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρxy, at low temperature, that transforms at a well-defined Néel transition temperature (TN) into a soft ferrimagnetic-like (FIM) state at high temperatures. In stark contrast, under tensile strain the low temperature canted AFM phase transitions to a state where ρxy is an order of magnitude smaller and therefore consistent with a low magnetisation phase. Neutron scattering confirms that the high temperature FIM-like phase of compressively strained films is magnetically ordered and the transition at TN is 1st-order. Our results open the field towards future exploration of electric-field driven piezospintronic and thin film caloric cooling applications in both Mn3NiN itself and the broader Mn3AN family.
Dion T, Arroo DM, Yamanoi K, et al., 2019, Tunable magnetization dynamics in artificial spin ice via shape anisotropy modification, Physical Review B, Vol: 100, ISSN: 2469-9950
Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected Ni80 Fe20 nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.
Das PK, Slawinska J, Vobornik I, et al., 2018, Role of spin-orbit coupling in the electronic structure of IrO2, Physical Review Materials, Vol: 2, ISSN: 2475-9953
The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rutile binary iridate, IrO2, is investigated. The detailed study of electronic bands measured on a high-quality single crystalline sample and use of a wide range of photon energy provide a huge improvement over the previous studies. The excellent agreement between theory and experimental results shows that the single-particle DFT description of IrO2 band structure is adequate, without the need of invoking any treatment of correlation effects. Although many observed features point to a 3D nature of the electronic structure, clear surface effects are revealed. The discussion of the orbital character of the relevant bands crossing the Fermi level sheds light on spin-orbit-coupling-driven phenomena in this material, unveiling a spin-orbit-induced avoided crossing, a property likely to play a key role in its large spin Hall effect.
Cal E, Qi J, Preedy O, et al., 2018, Functionalised magnetic nanoparticles for uranium adsorption with ultra-high capacity and selectivity, Journal of Materials Chemistry A, Vol: 6, Pages: 3063-3073, ISSN: 2050-7496
The removal of radioactive contaminants from the environment for safe and efficient waste disposal is a critical challenge, requiring the development of novel selective and high-capacity sequestering materials. In this paper the design of superparamagnetic iron oxide nanoparticles (SPIONs) as highly efficient magnetic-sorbent structures for uranium (U(VI)) separation is described. The nanosorbent was developed by surface functionalisation of single crystalline magnetite (Fe3O4) nanoparticles with a phosphate-based complex coating. This new design allowed for the development of a magnetically separable ultra-effective sorbent, with a measured U(VI) sorption capacity of ∼2333 mg U per g Fe (1690 mg U per g Fe3O4 NP), significantly higher than everything previously reported. Based on TEM analysis, it is proposed that these properties are the result of a multi-layer ligand structure, which enables a high degree of U-incorporation compared to conventional surface-ligand systems. Moreover, the phosphate-NP construct ((PO)x-Fe3O4) shows exceptionally high specificity for the sequestration of U(VI) in solution at pH 7. Adsorption tests in the presence of competing ions, such as Sr(II), Ca(II) and Mg(II), showed high selectivity of the nanoparticles for U(VI) and extremely rapid kinetics of contaminant removal from solution, with the total amount of uranyl ions being removed after only 60 seconds of contact with the NPs. The results presented in this paper highlight the potential of such a phosphate-functionalised magnetic nanosorbent as a highly effective material for the remediation of U(VI) from contaminated water and industrial scenarios.
Gartside JC, Arroo DM, Burn DM, et al., 2018, Realization of ground state in artificial kagome spin ice via topological defect-driven magnetic writing, Nature Nanotechnology, Vol: 13, Pages: 53-58, ISSN: 1748-3387
Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing-a scanning probe technique-provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy 'monopole-chain' states that exhibit negative effective temperatures.
Burn DM, Chadha M, Branford WR, 2017, Dynamic dependence to domain wall propagation through artificial spin ice, PHYSICAL REVIEW B, Vol: 95, ISSN: 2469-9950
Domain wall propagation dynamics has been studied in nanostructured artificial kagome spin-ice structures. A stripline circuit has been used to provide localized pulsed magnetic fields within the artificial spin-ice (ASI) structure. This provides control of the system through electrically assisted domain wall nucleation events. Synchronization of the pulsed fields with additional global magnetic fields and the use of a focused magneto-optical Kerr effect magnetometer allows our experiments to probe the domain wall transit through an extended ASI structure. We find that the propagation distance depends on the driving field revealing field-driven properties of domain walls below their intrinsic nucleation field.
Carter-Gartside J, Burn DM, Cohen LF, et al., 2016, A Novel Method for the Injection and Manipulation of Magnetic Charge States in Nanostructures, Scientific Reports, Vol: 6, ISSN: 2045-2322
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° 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° domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.
Zeissler K, Chadha M, Lovell E, et al., 2016, Low temperature and high field regimes of connected kagome artificial spin ice: the role of domain wall topology, Scientific Reports, Vol: 6, ISSN: 2045-2322
Artificial spin ices are frustrated magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, reversal occurs along one-dimensional chains by propagation of ferromagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching reversal path taken. However, magnetic reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use magnetic force microscopy to image the magnetic reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.
Burn DM, Chadha M, Branford WR, 2015, Angular-dependent magnetization reversal processes in artificial spin ice, Physical Review B - Condensed Matter and Materials Physics, Vol: 92, ISSN: 1098-0121
The angular dependence of the magnetization reversal in interconnected kagome artificial spin ice structures has been studied through experimental MOKE measurements and micromagnetic simulations. This reversal is mediated by the propagation of magnetic domain walls along the interconnecting bars, which either nucleate at the vertex or arrive following an interaction in a neighboring vertex. The physical differences in these processes show a distinct angular dependence allowing the different contributions to be identified. The configuration of the initial magnetization state, either locally or on a full sublattice of the system, controls the reversal characteristics of the array within a certain field window. This shows how the available magnetization reversal routes can be manipulated and the system can be trained.
Moseley D, Yates KA, Branford WR, et al., 2015, Signatures of filamentary superconductivity in antiferromagnetic BaFe2As2 single crystals, EPL, Vol: 111, ISSN: 0295-5075
Moseley DA, Yates KA, Peng N, et al., 2015, Magnetotransport of proton-irradiated BaFe2As2 and BaFe1.985Co0.015As2 single crystals, PHYSICAL REVIEW B, Vol: 91, ISSN: 1098-0121
Walton SK, Zeissler K, Burn DM, et al., 2015, Limitations in artificial spin ice path selectivity: the challenges beyond topological control, NEW JOURNAL OF PHYSICS, Vol: 17, ISSN: 1367-2630
Burn DM, Chadha M, Walton SK, et al., 2014, Dynamic interaction between domain walls and nanowire vertices, PHYSICAL REVIEW B, Vol: 90, ISSN: 1098-0121
Ladak S, Ball JM, Moseley D, et al., 2013, Observation of wrinkle induced potential drops in biased chemically derived graphene thin film networks, CARBON, Vol: 64, Pages: 35-44, ISSN: 0008-6223
Walton SK, Zeissler K, Branford WR, et al., 2013, MALTS: A Tool to Simulate Lorentz Transmission Electron Microscopy From Micromagnetic Simulations, IEEE TRANSACTIONS ON MAGNETICS, Vol: 49, Pages: 4795-4800, ISSN: 0018-9464
Zeissler K, Walton SK, Ladak S, et al., 2013, The non-random walk of chiral magnetic charge carriers in artificial spin ice, Scientific Reports, Vol: 3, ISSN: 2045-2322
Branford WR, 2012, Emergent magnetic monopoles in frustrated magnetic systems, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 370, Pages: 5702-5704, ISSN: 1364-503X
Ladak S, Walton SK, Zeissler K, et al., 2012, Disorder-independent control of magnetic monopole defect population in artificial spin-ice honeycombs, NEW JOURNAL OF PHYSICS, Vol: 14, ISSN: 1367-2630
Kumar K, Nightingale AM, Krishnadasan SH, et al., 2012, Direct synthesis of dextran-coated superparamagnetic iron oxide nanoparticles in a capillary-based droplet reactor, JOURNAL OF MATERIALS CHEMISTRY, Vol: 22, Pages: 4704-4708, ISSN: 0959-9428
Bhachu DS, Waugh MR, Zeissler K, et al., 2011, Textured Fluorine-Doped Tin Dioxide Films formed by Chemical Vapour Deposition, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 17, Pages: 11613-11621, ISSN: 0947-6539
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