Browsing by Author "Freeman, PG"

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    Development of the magnetic excitations of charge-stripe ordered La2-x Sr (x) NiO4 on doping towards checkerboard charge order
    (Springer, 2013-05-01) Freeman, PG; Giblin, SR; Hradil, K; Mole, RA; Prabhakaran, D
    The magnetic excitation spectrums of charge stripe ordered La2-x Sr (x) NiO4 x = 0.45 and x = 0.4 were studied by inelastic neutron scattering. We found the magnetic excitation spectrum of x = 0.45 from the ordered Ni2+ S = 1 spins to match that of checkerboard charge ordered La1.5Sr0.5NiO4. The distinctive asymmetry in the magnetic excitations above 40meV was observed for both doping levels, but an additional ferromagnetic mode was observed in x = 0.45 and not in the x = 0.4. We discuss the origin of crossover in the excitation spectrum between x = 0.45 and x = 0.4 with respect to discommensurations in the charge stripe structure. © 2013, Springer.
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    The instrument suite of the European Spallation Source
    (Elsevier B. V., 2020-01-10) Andersen, KH; Argyriou, DN; Jackson, AJ; Houston, J; Henry, PF; Deen, PP; Toft-Petersen, R; Beran, P; Strobl, M; Arnold, T; Wacklin-Knecht, H; Vivanco, R; Parker, SF; Gussen, A; Kanaki, K; Scionti, G; Olsen, MA; Arai, M; Schmakat, Ph; Lechner, RE; Niedermayer, Ch; Schneider, H; Zanetti, M; Petrillo, C; Moreira, FY; Stepanyan, S; Luna, P; Calzada, E; Stahn, J; Voigt, J; Dupont, T; Hanslik, R; Siemers, DJ; Udby, L; Chowdhury, MAH; Klauser, Ch; Rouijaa, M; Lehmann, E; Heynen, A; Bustinduy, I; Schwaab, A; Raspino, D; Scatigno, C; del Moral, OG; Kiehn, R; Aprigliano, G; Zanatta, M; Huerta, M; Bellissima, S; Lerche, M; Holm-Dahlin, S; Huerta, M; Christensen, NB; Lohstroh, W; Gorini, G; Fenske, J; Hansen, UB; Klauser, C; Rodrigues, S; Müller, M; Gorini, G; Bovo, C; Hall-Wilton, R; Fabrèges, X; Siemers, DJ; Khaplanov, A; Tsapatsaris, N; Taylor, J; Christensen, M; Schefer, J; Woracek, R; Tozzi, P; Müller, M; Carlsen, H; Olsen, MA; Orecchini, A; Di Fresco, L; Paciaroni, A; Bovo, C; Magán, M; Hauback, BC; Elmer, J; Heenan, RK; Piscitelli, F; Masi, F; Bakedano, G; Klimko, S; De Bonis, A; Fedrigo, A; Lukáš, P; Frielinghaus, H; Stahn, J; Schweika, W; Markó, M; Pfeiffer, D; Kirstein, O; Di Fresco, L; Schreyer, A; Orszulik, A; Nowak, G; Butterweck, S; Šaroun, J; Paciaroni, A; Kolevatov, R; Lehmann, EH; Filges, U; Schreyer, A; Koenen, M; Bustinduy, I; Magán, M; Feygenson, M; Cooper, JFK; Abad, E; Senesi, R; Longeville, S; Llamas-Jansa, I; Schulz, M; Birk, JO; Sharp, M; Galsworthy, P; Šaroun, J; Martínez, J; Hiess, A; Holm-Dahlin, S; Filges, U; Pullen, SA; Guyon Le Bouffy, J; Schefer, J; Lukáš, P; Udby, L; Kozielewski, T; Niedermayer, C; Sacchetti, F; Hartl, M; Jaksch, S; Salhi, Z; Brückel, T; Aguilar, J; Aguilar, J; Seifert, M; Bordallo, HN; Robillard, T; Villacorta, FJ; Herranz, I; del Rosso, L; Hauback, BC; Orecchini, A; Fabrèges, G; Fenske, J; Neuhaus, J; Schillinger, B; Abad, E; Kittelmann, T; Lefmann, K; Seifert, M; Neuhaus, J; Herranz, I; Kolevatov, R; Annighöfer, B; Oksanen, E; Morgano, M; Laszlo, G; Freeman, PG; Kennedy, SJ; Bertelsen, M; Bellissima, S; Alba-Simionesco, C; Markó, M; Mezei, F; Chowdhury, M; Halcrow, W; Jestin, J; Lieutenant, K; Babcock, E; Rønnow, HM; Engels, R; del Moral, OG; Vickery, A; Rouijaa, M; Lavie, P; Petersson Årsköld, S; Glavic, A; Désert, S; Mannix, D; Scatigno, C; Petry, W; Christensen, NB; Violini, N; Villacorta, FJ; Porcher, F; Glavic, A; Scionti, G; Zanetti, M; Fernandez-Alonso, F; Rønnow, HM; Mosconi, M; Olsson, M; Stepanyan, S; Petrillo, C; del Rosso, L; Harbott, P; Sacchetti, F; Bertelsen, M; Kämmerling, H; Andreani, C; Schulz, M; Colognesi, D; Luna, P; Loaiza, L; Turner, D; Martínez, JL; Tartaglione, A; Sordo, F; Llamas-Jansa, I; Schmakat, P; Lechner, RE; Poqué, A; Fernandez-Alonso, F; Colognesi, D; Tartaglione, A; Morgano, M; Webb, N; Loaiza, L; Whitelegg, L; Petry, W; Iversen, K; Vivanco, R; Tozzi, P; Goukassov, A; Schillinger, B; Carlsen, H; Masi, F; Christensen, M; Nowak, G; Nightingale, J; Schütz, S; Lopez, CI; Langridge, S; Schütz, S; Nagy, G; Zanatta, M; Andreani, C; Lefmann, K; Lohstroh, W; Mosconi, M; Senesi, R; Stefanescu, I; Bakedano, G; Hagen, ME; Wischnewski, A; Bourges, P; Hansen, UB; De Bonis, A; Kiehn, R; Parker, SF; Iversen, K; Sordo, F; Freeman, PG; Birk, JO; Rodríguez, DM; Ansell, S
    An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact of the early years of the ESS, and provide a solid base for completion and further expansion of the facility. © 2020 The Authors. Published by Elsevier B.V. Open access article under the CC BY-NC-ND license.
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    Jahn-Teller versus quantum effects in the spin-orbital material LuVO 3
    (American Physical Society, 2015-04-13) Skoulatos, M; Toth, S; Roessli, B; Enderle, M; Habicht, K; Sheptyakov, D; Cervellino, A; Freeman, PG; Reehuis, M; Stunault, A; McIntyre, GJ; Tung, LD; Marjerrison, C; Pomjakushina, E; Brown, PJ; Khomskii, DI; Rüegg, A; Kreyssig, A; Goldman, AI; Goff, JP
    We report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3 as driven by the orbital parameter. In particular, we distinguish between models based on orbital-Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity analysis of extended magnetic-excitation data sets. The results of this detailed study enabled us to draw definite conclusions about the classical versus quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3 and similar systems. © 2015 American Physical Society
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    Magnetic excitations of the charge stripe electrons below half doping in La2−xSrxNiO4 (x = 0.45, 0.4)
    (American Physical Society, 2017-02-03) Freeman, PG; Giblin, SR; Hradil, K; Mole, RA; Cermak, P; Prabhakaran, D
    The low energy magnetic excitation spectrum of charge stripe ordered La2-xSrxNiO4, x=0.4 and x=0.45 samples, were studied by neutron scattering. Two excitation modes are observed in both materials, one from the ordered magnetic moments, and a second mode consistent with pseudo-one-dimensional antiferromagnetic excitations of the charge stripe electrons (q-1D). The dispersion of the q-1D excitation follows the same relation as in x=1/3 composition, with even spectral weight in the two counterpropagating branches of the x=0.4 sample, however in the x=0.45 sample only one dispersion branch has any measurable spectral weight. The evolution of the q-1D excitations on doping to the checkerboard charge ordered phase is discussed. ©2017 American Physical Society.