Publications


Magnetic order and enhanced exchange in the quasi-one-dimensional molecule-based antiferromagnet Cu(NO3)2(pyz)3.

Physical chemistry chemical physics : PCCP 21 (2019) 1014-1018

BM Huddart, J Brambleby, T Lancaster, PA Goddard, F Xiao, SJ Blundell, FL Pratt, J Singleton, P Macchi, R Scatena, AM Barton, JL Manson

The quasi-one-dimensional molecule-based Heisenberg antiferromagnet Cu(NO3)2(pyz)3 has an intrachain coupling J = 13.7(1) K () and exhibits a state of long-range magnetic order below TN = 0.105(1) K. The ratio of interchain to intrachain coupling is estimated to be |J'/J| = 3.3 × 10-3, demonstrating a high degree of isolation for the Cu chains.


Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet alpha-Li2IrO3

PHYSICAL REVIEW B 99 (2019) ARTN 054426

S Choi, S Manni, J Singleton, CV Topping, T Lancaster, SJ Blundell, DT Adroja, V Zapf, P Gegenwart, R Coldea


Unconventional Field-Induced Spin Gap in an S=1/2 Chiral Staggered Chain.

Physical review letters 122 (2019) 057207-

J Liu, S Kittaka, RD Johnson, T Lancaster, J Singleton, T Sakakibara, Y Kohama, J van Tol, A Ardavan, BH Williams, SJ Blundell, ZE Manson, JL Manson, PA Goddard

We investigate the low-temperature magnetic properties of the molecule-based chiral spin chain [Cu(pym)(H_{2}O)_{4}]SiF_{6}·H_{2}O (pym=pyrimidine). Electron-spin resonance, magnetometry and heat capacity measurements reveal the presence of staggered g tensors, a rich low-temperature excitation spectrum, a staggered susceptibility, and a spin gap that opens on the application of a magnetic field. These phenomena are reminiscent of those previously observed in nonchiral staggered chains, which are explicable within the sine-Gordon quantum-field theory. In the present case, however, although the sine-Gordon model accounts well for the form of the temperature dependence of the heat capacity, the size of the gap and its measured linear field dependence do not fit with the sine-Gordon theory as it stands. We propose that the differences arise due to additional terms in the Hamiltonian resulting from the chiral structure of [Cu(pym)(H_{2}O)_{4}]SiF_{6}·H_{2}O, particularly a uniform Dzyaloshinskii-Moriya coupling and a fourfold periodic staggered field.


Manipulating quantum materials with quantum light

PHYSICAL REVIEW B 99 (2019) ARTN 085116

M Kiffner, JR Coulthard, F Schlawin, A Ardavan, D Jaksch


Ultrahigh critical current densities, the vortex phase diagram, and the effect of granularity of the stoichiometric high-T-c superconductor CaKFe4As4

PHYSICAL REVIEW MATERIALS 2 (2018) ARTN 074802

SJ Singh, M Bristow, WR Meier, P Taylor, SJ Blundell, PC Canfield, AI Coldea


Hyperfine interaction of individual atoms on a surface.

Science (New York, N.Y.) 362 (2018) 336-339

P Willke, Y Bae, K Yang, JL Lado, A Ferrón, T Choi, A Ardavan, J Fernández-Rossier, AJ Heinrich, CP Lutz

Taking advantage of nuclear spins for electronic structure analysis, magnetic resonance imaging, and quantum devices hinges on knowledge and control of the surrounding atomic-scale environment. We measured and manipulated the hyperfine interaction of individual iron and titanium atoms placed on a magnesium oxide surface by using spin-polarized scanning tunneling microscopy in combination with single-atom electron spin resonance. Using atom manipulation to move single atoms, we found that the hyperfine interaction strongly depended on the binding configuration of the atom. We could extract atom- and position-dependent information about the electronic ground state, the state mixing with neighboring atoms, and properties of the nuclear spin. Thus, the hyperfine spectrum becomes a powerful probe of the chemical environment of individual atoms and nanostructures.


Implications of bond disorder in a S=1 kagome lattice.

Scientific reports 8 (2018) 4745-4745

JL Manson, J Brambleby, PA Goddard, PM Spurgeon, JA Villa, J Liu, S Ghannadzadeh, F Foronda, J Singleton, T Lancaster, SJ Clark, IO Thomas, F Xiao, RC Williams, FL Pratt, SJ Blundell, CV Topping, C Baines, C Campana, B Noll

Strong hydrogen bonds such as F···H···F offer new strategies to fabricate molecular architectures exhibiting novel structures and properties. Along these lines and, to potentially realize hydrogen-bond mediated superexchange interactions in a frustrated material, we synthesized [H2F]2[Ni3F6(Fpy)12][SbF6]2 (Fpy = 3-fluoropyridine). It was found that positionally-disordered H2F+ ions link neutral NiF2(Fpy)4 moieties into a kagome lattice with perfect 3-fold rotational symmetry. Detailed magnetic investigations combined with density-functional theory (DFT) revealed weak antiferromagnetic interactions (J ~ 0.4 K) and a large positive-D of 8.3 K with ms = 0 lying below ms = ±1. The observed weak magnetic coupling is attributed to bond-disorder of the H2F+ ions which leads to disrupted Ni-F···H-F-H···F-Ni exchange pathways. Despite this result, we argue that networks such as this may be a way forward in designing tunable materials with varying degrees of frustration.


Comparative study of the magnetic properties of La3Ni2B ' O-9 for B ' = Nb, Ta or Sb

JOURNAL OF SOLID STATE CHEMISTRY 258 (2018) 825-834

C-M Chin, PD Battle, SJ Blundell, E Hunter, F Lang, M Hendrickx, RP Sena, J Hadermann


Observation of a crossover from nodal to gapped superconductivity in LuxZr1-xB12

PHYSICAL REVIEW B 98 (2018) ARTN 094505

FKK Kirschner, NE Sluchanko, VB Filipov, FL Pratt, C Baines, NY Shitsevalova, SJ Blundell


Publisher Correction: Magnetic edge states and coherent manipulation of graphene nanoribbons.

Nature 561 (2018) E31-

M Slota, A Keerthi, WK Myers, E Tretyakov, M Baumgarten, A Ardavan, H Sadeghi, CJ Lambert, A Narita, K Müllen, L Bogani

In Fig. 1 of this Letter, there should have been two nitrogen (N) atoms at the 1,3-positions of all the blue chemical structures (next to the oxygen atoms), rather than one at the 2-position. The figure has been corrected online, and the original incorrect figure is shown as Supplementary Information to the accompanying Amendment.


Author Correction: How to probe the spin contribution to momentum relaxation in topological insulators.

Nature communications 9 (2018) 729-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

The original version of this Article contained an error in the spelling of the author Benjamin H. Williams, which was incorrectly given as Benjamin H. Willams. This has now been corrected in both the PDF and HTML versions of the Article.


How to probe the spin contribution to momentum relaxation in topological insulators (vol 8, 2017)

NATURE COMMUNICATIONS 9 (2018) ARTN 729

M-S Nam, BH Willams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan


Author Correction: How to probe the spin contribution to momentum relaxation in topological insulators.

Nat Commun 9 (2018) 729-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

The original version of this Article contained an error in the spelling of the author Benjamin H. Williams, which was incorrectly given as Benjamin H. Willams. This has now been corrected in both the PDF and HTML versions of the Article.


Microscopic effects of Dy doping in the topological insulator Bi2Te3

PHYSICAL REVIEW B 97 (2018) ARTN 174427

LB Duffy, N-J Steinke, JA Krieger, AI Figueroa, K Kummer, T Lancaster, SR Giblin, FL Pratt, SJ Blundell, T Prokscha, A Suter, S Langridge, VN Strocov, Z Salman, G van der Laan, T Hesjedal


Magnetic edge states and coherent manipulation of graphene nanoribbons.

Nature 557 (2018) 691-695

M Slota, A Keerthi, WK Myers, E Tretyakov, M Baumgarten, A Ardavan, H Sadeghi, CJ Lambert, A Narita, K Müllen, L Bogani

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths2,3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons5,6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.


Electrically controlled nuclear polarization of individual atoms.

Nature nanotechnology (2018)

K Yang, P Willke, Y Bae, A Ferrón, JL Lado, A Ardavan, J Fernández-Rossier, AJ Heinrich, CP Lutz

Nuclear spins serve as sensitive probes in chemistry1 and materials science2 and are promising candidates for quantum information processing3-6. NMR, the resonant control of nuclear spins, is a powerful tool for probing local magnetic environments in condensed matter systems, which range from magnetic ordering in high-temperature superconductors7,8 and spin liquids9 to quantum magnetism in nanomagnets10,11. Increasing the sensitivity of NMR to the single-atom scale is challenging as it requires a strong polarization of nuclear spins, well in excess of the low polarizations obtained at thermal equilibrium, as well as driving and detecting them individually4,5,12. Strong nuclear spin polarization, known as hyperpolarization, can be achieved through hyperfine coupling with electron spins2. The fundamental mechanism is the conservation of angular momentum: an electron spin flips and a nuclear spin flops. The nuclear hyperpolarization enables applications such as in vivo magnetic resonance imaging using nanoparticles13, and is harnessed for spin-based quantum information processing in quantum dots14 and doped silicon15-17. Here we polarize the nuclear spins of individual copper atoms on a surface using a spin-polarized current in a scanning tunnelling microscope. By employing the electron-nuclear flip-flop hyperfine interaction, the spin angular momentum is transferred from tunnelling electrons to the nucleus of individual Cu atoms. The direction and magnitude of the nuclear polarization is controlled by the direction and amplitude of the current. The nuclear polarization permits the detection of the NMR of individual Cu atoms, which is used to sense the local magnetic environment of the Cu electron spin.


Doped Sr2FeIrO6-Phase Separation and a Jeff ≠ 0 State for Ir5.

Inorganic chemistry 57 (2018) 10303-10311

JE Page, CV Topping, A Scrimshire, PA Bingham, SJ Blundell, MA Hayward

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr2FeIrO6 adopts an I1̅ symmetry double perovskite structure with an a-b-c- tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1̅ phase and a cation-substituted, P21/ n symmetry, a-a-c+ distorted double perovskite phase. Magnetization, neutron diffraction, and 57Fe Mössbauer data show that, in common with Sr2FeIrO6, the cation substituted Sr2- xA xFe1- yGa yIrO6 phases undergo transitions to type-II antiferromagnetically ordered states at TN ∼ 120 K. However, in contrast to stoichiometric Sr2FeIrO6, cation substituted samples exhibit a further magnetic transition at TA ∼ 220 K, which corresponds to the ordering of Jeff ≠ 0 Ir5+ centers in the cation-substituted, P21/ n symmetry, double perovskite phases.


Proposal for the detection of magnetic monopoles in spin ice via nanoscale magnetometry

PHYSICAL REVIEW B 97 (2018) ARTN 140402

FKK Kirschner, F Flicker, A Yacoby, NY Yao, SJ Blundell


Quantum magnetism in molecular spin ladders probed with muonspin spectroscopy

NEW JOURNAL OF PHYSICS 20 (2018) ARTN 103002

T Lancaster, F Xiao, BM Huddart, RC Williams, FL Pratt, SJ Blundell, SJ Clark, R Scheuermann, T Goko, S Ward, JL Manson, C Ruegg, KW Kramer


Magnetic phases of skyrmion-hosting GaV4S8-ySey (y=0, 2, 4, 8) probed with muon spectroscopy

PHYSICAL REVIEW B 98 (2018) ARTN 054428

KJA Franke, BM Huddart, TJ Hicken, F Xiao, SJ Blundell, FL Pratt, M Crisanti, JAT Barker, SJ Clark, A Stefancic, MC Hatnean, G Balakrishnan, T Lancaster

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