Magnetically induced metal-insulator transition in Pb2CaOsO6

PHYSICAL REVIEW B 102 (2020) ARTN 214409

H Jacobsen, HL Feng, AJ Princep, MC Rahn, Y Guo, J Chen, Y Matsushita, Y Tsujimoto, M Nagao, D Khalyavin, P Manuel, CA Murray, C Donnerer, JG Vale, MM Sala, K Yamaura, AT Boothroyd

Magnetically driven loss of centrosymmetry in metallic Pb2CoOsO6

PHYSICAL REVIEW B 102 (2020) ARTN 104410

AJ Princep, HL Feng, YF Guo, F Lang, HM Weng, P Manuel, D Khalyavin, A Senyshyn, MC Rahn, YH Yuan, Y Matsushita, SJ Blundell, K Yamaura, AT Boothroyd

Resonant x-ray scattering study of diffuse magnetic scattering from the topological semimetals EuCd2As2 and EuCd2Sb2

PHYSICAL REVIEW B 102 (2020) ARTN 014408

J-R Soh, E Schierle, Y Yan, H Su, D Prabhakaran, E Weschke, Y-F Guo, YF Shi, AT Boothroyd

Approaching the quantum critical point in a highly correlated all-in-all-out antiferromagnet

PHYSICAL REVIEW B 101 (2020) ARTN 220404

Y Wang, TF Rosenbaum, D Prabhakaran, AT Boothroyd, Y Feng

Ground-state magnetic structure of Mn3Ge

PHYSICAL REVIEW B 101 (2020) ARTN 140411

J-R Soh, F de Juan, N Qureshi, H Jacobsen, H-Y Wang, Y-F Guo, AT Boothroyd

Strong quantum fluctuations from competition between magnetic phases in a pyrochlore iridate (vol 101, 104404, 2020)

PHYSICAL REVIEW B 101 (2020) ARTN 169901

H Jacobsen, CD Dashwood, E Lhotel, D Khalyavin, P Manuel, R Stewart, D Prabhakaran, DF McMorrow, AT Boothroyd

Strong quantum fluctuations from competition between magnetic phases in a pyrochlore iridate

PHYSICAL REVIEW B 101 (2020) ARTN 104404

H Jacobsen, CD Dashwood, E Lhotel, D Khalyavin, P Manuel, R Stewart, D Prabhakaran, DF McMorrow, AT Boothroyd

Role of defects in determining the magnetic ground state of ytterbium titanate.

Nature communications 10 (2019) 637-

DF Bowman, E Cemal, T Lehner, AR Wildes, L Mangin-Thro, GJ Nilsen, MJ Gutmann, DJ Voneshen, D Prabhakaran, AT Boothroyd, DG Porter, C Castelnovo, K Refson, JP Goff

Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer behaviour associated with large quantum fluctuations. Whether the magnetic ground state of Yb<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub> is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. Here we have determined the role of structural defects on the magnetic ground state via the diffuse scattering of neutrons. We find that oxygen vacancies stabilise the spin liquid phase and the stuffing of Ti sites by Yb suppresses it. Samples in which the oxygen vacancies have been eliminated by annealing in oxygen exhibit a transition to a ferromagnetic phase, and this is the true magnetic ground state.

Monitoring ultrafast metallization in LaCoO3 with femtosecond soft x-ray spectroscopy


M Izquierdo, M Karolak, D Prabhakaran, AT Boothroyd, AO Scherz, A Lichtenstein, SL Molodtsov

An ideal Weyl semimetal induced by magnetic exchange

Physical review B: Condensed matter and materials physics American Physical Society 100 (2019) 201102(R)

J-R Soh, F De Juan, M Vergniory, N Schroeter, M Rahn, DY Yan, J Jiang, M Bristow, P Reiss, J Blandy, Y Guo, Y Shi, T Kim, A McCollam, S Simon, Y Chen, A Coldea, A Boothroyd

Magnetic and electronic structure of Dirac semimetal candidate EuMnSb2

Physical Review B American Physical Society 100 (2019) 174406

J-R Soh, P Manuel, NMB Schroeter, CJ Yi, F Orlandi, YG Shi, D Prabhakaran, A Boothroyd

We report an experimental study of the magnetic order and electronic structure and transport of the layered pnictide EuMnSb2, performed using neutron diffraction, angle-resolved photoemission spectroscopy (ARPES), and magnetotransport measurements. We find that the Eu and Mn sublattices display antiferromagnetic (AFM) order below T EuN = 21(1) K and T MnN = 350(2) K, respectively. The former can be described by an A-type AFM structure with the Eu spins aligned along the c axis (an in-plane direction), whereas the latter has a C-type AFM structure with Mn moments along the a -axis (perpendicular to the layers). The ARPES spectra reveal Dirac-like linearly dispersing bands near the Fermi energy. Furthermore, our magnetotransport measurements show strongly anisotropic magnetoresistance and indicate that the Eu sublattice is intimately coupled to conduction electron states near the Dirac point.

Magnetic structure and excitations of the topological semimetal YbMnBi2

PHYSICAL REVIEW B 100 (2019) ARTN 144431

J-R Soh, H Jacobsen, B Ouladdiaf, A Ivanov, A Piovano, T Tejsner, Z Feng, H Wang, H Su, Y Guo, Y Shi, AT Boothroyd

Magnetic structure and excitations of the topological semimetal YbMnBi2

Physical Review B American Physical Society 100 (2019) 144431

J-R Soh, H Jacobsen, B Ouladdiaf, A Ivanov, A Piovano, T Tejsner, Z Feng, H Wang, H Su, Y Guo, Y Shi, A Boothroyd

We investigated the magnetic structure and dynamics of YbMnBi2, with elastic and inelastic neutron scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We confirm C-type antiferromagnetic ordering of the Mn spins below TN = 290 K and determine that the spins point along the c axis to within about 3◦. The observed magnon spectrum can be described very well by the same effective spin Hamiltonian that was used previously to model the magnon spectrum of CaMnBi2. Our results show conclusively that the creation of Weyl nodes in YbMnBi2 by the time-reversal symmetry-breaking mechanism can be excluded in the bulk.

Selective probing of magnetic order on Tb and Ir sites in stuffed Tb2Ir2O7  using resonant x-ray scattering.

Journal of physics. Condensed matter : an Institute of Physics journal 31 (2019) 344001-344001

C Donnerer, MC Rahn, E Schierle, RS Perry, LSI Veiga, G Nisbet, SP Collins, D Prabhakaran, AT Boothroyd, DF McMorrow

We study the magnetic structure of the 'stuffed' (Tb-rich) pyrochlore iridate Tb2+x Ir2-x O7-y  (x ∼ 0.18), using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L 3 and Tb M 5 edges, which provide selective sensitivity to Ir 5d and Tb 4f  magnetic moments, respectively. At the Ir L 3 edge, we found the onset of long-range [Formula: see text] magnetic order below [Formula: see text] K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS cross-sections, we estimate an ordered magnetic moment of [Formula: see text] at 5 K. At the Tb M 5 edge, long-range [Formula: see text] magnetic order appeared below  ∼[Formula: see text] K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M 5 edge in applied magnetic fields up to 6 T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which [Formula: see text] K and [Formula: see text], indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.

Evidence for a J(eff)=0 ground state and defect-induced spin glass behavior in the pyrochlore osmate Y2Os2O7

PHYSICAL REVIEW B 99 (2019) ARTN 174442

NR Davies, CV Topping, H Jacobsen, AJ Princep, FKK Kirschner, MC Rahn, M Bristow, JG Vale, I da Silva, PJ Baker, CJ Sahle, Y-F Guo, D-Y Yan, Y-G Shi, SJ Blundell, DF McMorrow, AT Boothroyd

First-order valence transition: Neutron diffraction, inelastic neutron scattering, and x-ray absorption investigations on the double perovskite Ba2PrRu0.9Ir0.1O6

Physical Review B American Physical Society 99 (2019) 184440

J Sannigrahi, DT Adroja, C Ritter, W Kockelmann, AD Hillier, KS Knight, A Boothroyd, M Wakeshima, Y Hinatsu, JFW Mosselmans, S Ramos

Bulk studies have revealed a first-order valence phase transition in Ba2PrRu1−xIrxO6 (0.10 ≤ x ≤ 0.25), which is absent in the parent compounds with x = 0 (Pr3+) and x = 1 (Pr4+), which exhibit antiferromagnetic order with transition temperatures TN = 120 and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering and x-ray absorption measurements to investigate the nature of the Pr ion in x = 0.1. The magnetic susceptibility and heat capacity of x = 0.1 show a clear sign of the first order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that x = 0.1 crystallizes in a monoclinic structure with space group P21/n at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one (Fm3m) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the x = 0.1 compound below 110 K in the neutron diffraction measurements. Meanwhile the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined highenergy magnetic excitations near 264 meV at temperatures below the valence transition. Low energy INS data show a broad magnetic excitation centred at 50 meV above the valence transition, but four well-defined magnetic excitations at 7 K. The high energy excitations are assigned to the Pr4+ ions in the cubic phase and the low energy excitations to the Pr3+ ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. The results on the x = 0.1 compound are compared with those for x = 0 and 1.

Tuning of the Ru4+ ground-state orbital population in the 4d(4) Mott insulator Ca2RuO4 achieved by La doping

PHYSICAL REVIEW B 99 (2019) ARTN 075125

D Pincini, LSI Veiga, CD Dashwood, F Forte, M Cuoco, RS Perry, P Bencok, AT Boothroyd, DF McMorrow

Paramagnon dispersion in beta-FeSe observed by Fe L-edge resonant inelastic x-ray scattering

Physical review B: Condensed matter and materials physics American Physical Society (2019)

M Rahn, K Kummer, N Brookes, A Haghighirad, K Gilmore, ANDREW BOOTHROYD

Probing the intrinsic and extrinsic origins of piezoelectricity in lead zirconate titanate single crystals

Journal of Applied Crystallography International Union of Crystallography 51 (2018) 1396-1403

N Zhang, S Gorfman, H Choe, T Vergentev, V Dyadkin, H Yokota, D Chernyshov, B Wang, A Glazer, W Ren, Z-G Ye

The physical origin of the piezoelectric effect has been the focus of much research work. While it is commonly accepted that the origins of piezoelectricity may be intrinsic (related to the change of lattice parameters) and extrinsic (related to the movement of domain walls), their separation is often a challenging experimental task. Here in situ high-resolution synchrotron X-ray diffraction has been combined with a new data analysis technique to characterize the change of the lattice parameters and domain microstructure of a PbZr1−xTixO3 (x = 0.45) crystal under an external electric field. It is shown how `effective piezoelectric coefficients' evolve upon the transition from purely `intrinsic' effects to `extrinsic' ones due to domain-wall motion. This technique and corresponding data analysis can be applied to broader classes of materials and provide important insights into the microscopic origin of their physical properties.

Magnetic and electronic structure of the layered rare-earth pnictide EuCd2Sb2

Physical Review B American Physical Society 98 (2018) 064419-

J Soh, C Donnerer, KM Hughes, E Schierle, E Weschke, D Prabhakaran, A Boothroyd

Resonant elastic X-ray scattering (REXS) at the Eu M5 edge reveals an antiferromagnetic structure in layered EuCd2Sb2 at temperatures below TN = 7.4 K with a magnetic propagation vector of (0, 0, 1/2) and spins in the basal plane. Magneto-transport and REXS measurements with an in-plane magnetic field show that features in the magnetoresistance are correlated with changes in the magnetic structure induced by the field. Ab initio electronic structure calculations predict that the observed spin structure gives rise to a gapped Dirac point close to the Fermi level with a gap of ∆E ∼ 0.01 eV. The results of this study indicate that the Eu spins are coupled to conduction electron states near the Dirac point.