The Full Magnon Spectrum of Yttrium Iron Garnet

npj Quantum Materials (2017)

Princep, RA Ewings, S Ward, S Toth, C Dubs, D Prabhakaran, AT Boothroyd

Probing the Topological Surface State in Bi2Se3 Thin Films Using Temperature-Dependent Terahertz Spectroscopy

ACS PHOTONICS 4 (2017) 2711-2718

VS Kamboj, A Singh, T Ferrus, HE Beere, LB Dufry, T Hesjedal, CHW Barnes, DA Ritchie

Codoping of Sb2Te3 thin films with V and Cr


LB Duffy, AI Figueroa, G van der Laan, T Hesjedal

Correction to Step-Flow Growth of Bi 2 Te 3 Nanobelts

Crystal Growth & Design 17 (2017) 1438-1438

P Schönherr, T Tilbury, H Wang, AA Haghighirad, V Srot, PA van Aken, T Hesjedal

Temperature-induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi0.9Sm0.1FeO3 driven by f-d induced magnetic anisotropy

PHYSICAL REVIEW B 95 (2017) ARTN 054420

RD Johnson, PA McClarty, DD Khalyavin, P Manuel, P Svedlindh, CS Knee

Electrical Switching of Magnetic Polarity in a Multiferroic BiFeO3 Device at Room Temperature


NW Price, RD Johnson, W Saenrang, A Bombardi, FP Chmiel, CB Eom, PG Radaelli

Layer-by-layer epitaxial thin films of the pyrochlore Tb2Ti2O7.

Nanotechnology 28 (2017) 055708-

L Bovo, CM Rouleau, D Prabhakaran, ST Bramwell

Layer-by-layer epitaxial growth of the pyrochlore magnet Tb2Ti2O7 on the isostructural substrate Y2Ti2O7 results in high-quality single crystal films of up to 60 nm thickness. Substrate-induced strain is shown to act as a strong and controlled perturbation to the exotic magnetism of Tb2Ti2O7, opening up the general prospect of strain-engineering the diverse magnetic and electrical properties of pyrochlore oxides.

Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations


A Baker, M Beg, G Ashton, M Albert, D Chernyshenko, W Wang, S Zhang, M-A Bisotti, M Franchin, CL Hu, R Stamps, T Hesjedal, H Fangohr

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb_{2}Ti_{2}O_{7} in a Magnetic Field.

Physical review letters 119 (2017) 057203-

JD Thompson, PA McClarty, D Prabhakaran, I Cabrera, T Guidi, R Coldea

The frustrated pyrochlore magnet Yb_{2}Ti_{2}O_{7} has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.

Broken rotational symmetry on the Fermi surface of a high-Tc superconductor

npj Quantum Materials 2 (2017)

BJ Ramshaw, N Harrison, SE Sebastian, S Ghannadzadeh, KA Modic, DA Bonn, WN Hardy, R Liang, PA Goddard

Magnetic excitations of the charge stripe electrons below half doping in La2-xSrxNiO4 (x=0.45, 0.4)

PHYSICAL REVIEW B 95 (2017) ARTN 064403

PG Freeman, SR Giblin, K Hradil, RA Mole, P Cermak, D Prabhakaran

Direct experimental determination of the topological winding number of skyrmions in Cu2OSeO3.

Nature communications 8 (2017) 14619-

SL Zhang, G van der Laan, T Hesjedal

The mathematical concept of topology has brought about significant advantages that allow for a fundamental understanding of the underlying physics of a system. In magnetism, the topology of spin order manifests itself in the topological winding number which plays a pivotal role for the determination of the emergent properties of a system. However, the direct experimental determination of the topological winding number of a magnetically ordered system remains elusive. Here, we present a direct relationship between the topological winding number of the spin texture and the polarized resonant X-ray scattering process. This relationship provides a one-to-one correspondence between the measured scattering signal and the winding number. We demonstrate that the exact topological quantities of the skyrmion material Cu2OSeO3 can be directly experimentally determined this way. This technique has the potential to be applicable to a wide range of materials, allowing for a direct determination of their topological properties.

Combining microscopic and macroscopic probes to untangle the single-ion anisotropy and exchange energies in an S=1 quantum antiferromagnet

PHYSICAL REVIEW B 95 (2017) ARTN 134435

J Brambleby, JL Manson, PA Goddard, MB Stone, RD Johnson, P Manuel, JA Villa, CM Brown, H Lu, S Chikara, V Zapf, SH Lapidus, R Scatena, P Macchi, Y-S Chen, L-C Wu, J Singleton

Anomalous behavior of displacement correlation function and strain in lanthanum cobalt oxide analyzed both from X-ray powder diffraction and EXAFS data

POWDER DIFFRACTION 32 (2017) S151-S154

V Efimov, V Sikolenko, IO Troyanchuk, D Karpinsky, E Efimova, SI Tiutiunnikov, BN Savenko, D Novoselov, D Prabhakaran

Formation of Hubbard-like bands as a fingerprint of strong electron-electron interactions in FeSe

PHYSICAL REVIEW B 95 (2017) ARTN 081106

MD Watson, S Backes, AA Haghighirad, M Hoesch, TK Kim, AI Coldea, R Valenti

Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

PHYSICAL REVIEW B 95 (2017) ARTN 024404

J Brambleby, PA Goddard, J Singleton, M Jaime, T Lancaster, L Huang, J Wosnitza, CV Topping, KE Carreiro, HE Tran, ZE Manson, JL Manson

Suppression of electronic correlations by chemical pressure from FeSe to FeS

Phys. Rev. B 96, 121103(R) (2017) American Physical Society (2017)

P Reiss, MD Watson, TK Kim, AA Haghighirad, DN Woodruff, M Bruma, SJ Clarke, AI Coldea

Iron-based chalcogenides are complex superconducting systems in which orbitally-dependent electronic correlations play an important role. Here, using high-resolution angle-resolved photoemission spectroscopy, we investigate the effect of these electronic correlations outside the nematic phase in the tetragonal phase of superconducting FeSe1-xSx (x = 0; 0:18; 1). With increasing sulfur substitution, the Fermi velocities increase significantly and the band renormalizations are suppressed towards a factor of 1.5-2 for FeS. Furthermore, the chemical pressure leads to an increase in the size of the quasi-two dimensional Fermi surface, compared with that of FeSe, however, it remains smaller than the predicted one from first principle calculations for FeS. Our results show that the isoelectronic substitution is an effective way to tune electronic correlations in FeSe1-xSx, being weakened for FeS with a lower superconducting transition temperature. This suggests indirectly that electronic correlations could help to promote higher-Tc superconductivity in FeSe.

Strain and Magnetic Field Induced Spin-Structure Transitions in Multiferroic BiFeO3


A Agbelele, D Sando, C Toulouse, C Paillard, RD Johnson, R Ruffer, AF Popkov, C Carretero, P Rovillain, J-M Le Breton, B Dkhil, M Cazayous, Y Gallais, M-A Measson, A Sacuto, P Manuel, AK Zvezdin, A Barthelemy, J Juraszek, M Bibes

On the temperature dependence of spin pumping in ferromagnet-topological insulator-ferromagnet spin valves

Results in Physics 6 (2016) 293-294

AA Baker, AI Figueroa, G van der Laan, T Hesjedal

Experimental and Theoretical Electron Density Analysis of Copper Pyrazine Nitrate Quasi-Low-Dimensional Quantum Magnets.

Journal of the American Chemical Society 138 (2016) 2280-2291

LHR Dos Santos, A Lanza, AM Barton, J Brambleby, WJA Blackmore, PA Goddard, F Xiao, RC Williams, T Lancaster, FL Pratt, SJ Blundell, J Singleton, JL Manson, P Macchi

The accurate electron density distribution and magnetic properties of two metal-organic polymeric magnets, the quasi-one-dimensional (1D) Cu(pyz)(NO3)2 and the quasi-two-dimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by high-resolution single-crystal X-ray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchange-coupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the Cu-Cu superexchange pathway mediated by the pyrazine bridging ligands, via a σ-type interaction. From topological analyses of experimental charge-density data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)-pyz coordination polymers.