Imperial College London

DrWillBranford

Faculty of Natural SciencesDepartment of Physics

Reader in Solid State Physics
 
 
 
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Contact

 

+44 (0)20 7594 6674w.branford Website

 
 
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Location

 

912Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

88 results found

Chaurasiya AK, Mondal AK, Gartside JC, Stenning KD, Vanstone A, Barman S, Branford WR, Barman Aet 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

Journal article

Gartside JC, Vanstone A, Dion T, Stenning KD, Arroo DM, Kurebayashi H, Branford Wet 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 model host systems for reconfigurable magnonics. The strong inter-element coupling allows for stark spectral differences across a broad microstate space due to shifts in the dipolar field landscape. While these systems have yielded impressive initial results, developing rapid, scaleable means to access a broad range of spectrally-distinct microstates is an open research problem. We present a scheme whereby square artificial spin ice is modified by widening a ‘staircase’ subset of bars relative to the rest of the array, allowing preparation 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 spectra observed. Microstate-dependent mode-hybridisation and anticrossings are observed at both remanence and in-field with dynamic coupling strength tunable via microstate-selection. Experimental coupling strengths are found up to g/2π = 0.16 GHz. Microstate control allows fine mode-frequency shifting, gap creation and closing, and active mode number selection.

Journal article

Gartside JC, Vanstone A, Dion T, Stenning KD, Arroo DM, Kurebayashi H, Branford WRet al., 2021, Reconfigurable magnonic mode-hybridisation and spectral control in a bicomponent artificial spin ice, Publisher: arXiv

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.

Working paper

Stenning KD, Gartside JC, Dion T, Vanstone A, Arroo DM, Branford WRet 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.

Journal article

Gartside JC, Jung SG, Yoo SY, Arroo DM, Vanstone A, Dion T, Stenning KD, Branford WRet al., 2020, Current-controlled nanomagnetic writing for reconfigurable magnonic crystals (vol 3, 219, 2020), Communications Physics, Vol: 3, Pages: 1-1, ISSN: 2399-3650

Journal article

Gartside JC, Jung SG, Yoo SY, Arroo DM, Vanstone A, Dion T, Stenning KD, Branford WRet al., 2020, Current-controlled nanomagnetic writing for reconfigurable magnonic crystals, Communications Physics, Vol: 3, 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.

Journal article

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.

Journal article

Cohen L, Boldrin D, Johnson F, Thompson R, Mihai AP, Zou B, Griffiths J, Gubeljak P, Ormandy KL, Manuel P, Khalyavin DD, Ouladdiaf B, Petrov P, Branford W, Cohen LFet 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.

Journal article

Dion T, Arroo DM, Yamanoi K, Kimura T, Gartside JC, Cohen LF, Kurebayashi H, Branford WRet 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.

Journal article

Das PK, Slawinska J, Vobornik I, Fujii J, Regoutz A, Kahk JM, Scanlon DO, Morgan BJ, McGuinness C, Plekhanov E, Di Sante D, Huang Y-S, Chen R-S, Rossi G, Picozzi S, Branford WR, Panaccione G, Payne DJet 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.

Journal article

Cal E, Qi J, Preedy O, Chen S, Boldrin D, Branford WR, Vandeperre L, Ryan MPet 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.

Journal article

Gartside JC, Arroo DM, Burn DM, Bemmer VL, Moskalenko A, Cohen LF, Branford WRet 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.

Journal article

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.

Journal article

Carter-Gartside J, Burn DM, Cohen LF, Branford WRet 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.

Journal article

Zeissler K, Chadha M, Lovell E, Cohen LF, Branford WRet 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.

Journal article

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.

Journal article

Moseley D, Yates KA, Branford WR, Sefat AS, Mandrus D, Stuard SJ, Salem-Sugui S, Ghivelder L, Cohen LFet al., 2015, Signatures of filamentary superconductivity in antiferromagnetic BaFe2As2 single crystals, EPL, Vol: 111, ISSN: 0295-5075

Journal article

Moseley DA, Yates KA, Peng N, Mandrus D, Sefat AS, Branford WR, Cohen LFet al., 2015, Magnetotransport of proton-irradiated BaFe2As2 and BaFe1.985Co0.015As2 single crystals, PHYSICAL REVIEW B, Vol: 91, ISSN: 1098-0121

Journal article

Walton SK, Zeissler K, Burn DM, Ladak S, Read DE, Tyliszczak T, Cohen LF, Branford WRet al., 2015, Limitations in artificial spin ice path selectivity: the challenges beyond topological control, NEW JOURNAL OF PHYSICS, Vol: 17, ISSN: 1367-2630

Journal article

Burn DM, Chadha M, Walton SK, Branford WRet al., 2014, Dynamic interaction between domain walls and nanowire vertices, PHYSICAL REVIEW B, Vol: 90, ISSN: 1098-0121

Journal article

Ladak S, Ball JM, Moseley D, Eda G, Branford WR, Chhowalla M, Anthopoulos TD, Cohen LFet 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

Journal article

Walton SK, Zeissler K, Branford WR, Felton Set 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

Journal article

Zeissler K, Walton SK, Ladak S, Read DE, Tyliszczak T, Cohen LF, Branford WRet al., 2013, The non-random walk of chiral magnetic charge carriers in artificial spin ice, Scientific Reports, Vol: 3, ISSN: 2045-2322

Journal article

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

Journal article

Ladak S, Walton SK, Zeissler K, Tyliszczak T, Read DE, Branford WR, Cohen LFet al., 2012, Disorder-independent control of magnetic monopole defect population in artificial spin-ice honeycombs, NEW JOURNAL OF PHYSICS, Vol: 14, ISSN: 1367-2630

Journal article

Branford WR, Ladak S, Read DE, Zeissler K, Cohen LFet al., 2012, Emerging Chirality in Artificial Spin Ice, SCIENCE, Vol: 335, Pages: 1597-1600, ISSN: 0036-8075

Journal article

Kumar K, Nightingale AM, Krishnadasan SH, Kamaly N, Wylenzinska-Arridge M, Zeissler K, Branford WR, Ware E, deMello AJ, deMello JCet 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

Journal article

Bhachu DS, Waugh MR, Zeissler K, Branford WR, Parkin IPet 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

Journal article

Ladak S, Read D, Tyliszczak T, Branford WR, Cohen LFet al., 2011, Monopole defects and magnetic Coulomb blockade, NEW JOURNAL OF PHYSICS, Vol: 13, ISSN: 1367-2630

Journal article

Leontiadou MA, Litvinenko KL, Gilbertson AM, Pidgeon CR, Branford WR, Cohen LF, Fearn M, Ashley T, Emeny MT, Murdin BN, Clowes SKet al., 2011, Experimental determination of the Rashba coefficient in InSb/InAlSb quantum wells at zero magnetic field and elevated temperatures, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 23, ISSN: 0953-8984

Journal article

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