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Nikitin SE, Fåk B, Krämer KW, Fennell T, Normand B, Läuchli AM, Rüegg C. Thermal Evolution of Dirac Magnons in the Honeycomb Ferromagnet CrBr_{3}. Phys Rev Lett 2022; 129:127201. [PMID: 36179160 DOI: 10.1103/physrevlett.129.127201] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Accepted: 08/17/2022] [Indexed: 06/16/2023]
Abstract
CrBr_{3} is an excellent realization of the two-dimensional honeycomb ferromagnet, which offers a bosonic equivalent of graphene with Dirac magnons and topological character. We perform inelastic neutron scattering measurements using state-of-the-art instrumentation to update 50-year-old data, thereby enabling a definitive comparison both with recent experimental claims of a significant gap at the Dirac point and with theoretical predictions for thermal magnon renormalization. We demonstrate that CrBr_{3} has next-neighbor J_{2} and J_{3} interactions approximately 5% of J_{1}, an ideal Dirac magnon dispersion at the K point, and the associated signature of isospin winding. The magnon lifetime and the thermal band renormalization show the universal T^{2} evolution expected from an interacting spin-wave treatment, but the measured dispersion lacks the predicted van Hove features, pointing to the need for more sophisticated theoretical analysis.
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Affiliation(s)
- S E Nikitin
- Quantum Criticality and Dynamics Group, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland
| | - B Fåk
- Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France
| | - K W Krämer
- Department of Chemistry, Biochemistry and Pharmacy, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - B Normand
- Laboratory for Theoretical and Computational Physics, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland
- Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - A M Läuchli
- Laboratory for Theoretical and Computational Physics, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland
- Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ch Rüegg
- Quantum Criticality and Dynamics Group, Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland
- Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute for Quantum Electronics, ETH Zürich, CH-8093 Hönggerberg, Switzerland
- Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland
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Giblin SR, Twengström M, Bovo L, Ruminy M, Bartkowiak M, Manuel P, Andresen JC, Prabhakaran D, Balakrishnan G, Pomjakushina E, Paulsen C, Lhotel E, Keller L, Frontzek M, Capelli SC, Zaharko O, McClarty PA, Bramwell ST, Henelius P, Fennell T. Pauling Entropy, Metastability, and Equilibrium in Dy_{2}Ti_{2}O_{7} Spin Ice. Phys Rev Lett 2018; 121:067202. [PMID: 30141658 DOI: 10.1103/physrevlett.121.067202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Indexed: 06/08/2023]
Abstract
Determining the fate of the Pauling entropy in the classical spin ice material Dy_{2}Ti_{2}O_{7} with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice-the dipolar spin ice model-predicts an ordering transition at T≈0.15 K, but recent experiments by Pomaranski et al. suggest an entropy recovery over long timescales at temperatures as high as 0.5 K, much too high to be compatible with the theory. Using neutron scattering and specific heat measurements at low temperatures and with long timescales (0.35 K/10^{6} s and 0.5 K/10^{5} s, respectively) on several isotopically enriched samples, we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Furthermore, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez et al. are, after all, essentially correct: The short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.
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Affiliation(s)
- S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - M Twengström
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - L Bovo
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
- Department of Innovation and Enterprise, University College London, 90 Tottenham Court Road, Fitzrovia, London W1T 4TJ, United Kingdom
| | - M Ruminy
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Bartkowiak
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P Manuel
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - J C Andresen
- Department of Physics, Ben Gurion University of the Negev, Beer Sheva 84105, Israel
| | - D Prabhakaran
- Clarendon Laboratory, Physics Department, Oxford University, Oxford, OX1 3PU, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - E Pomjakushina
- Laboratory for Scientific Developments, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - C Paulsen
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - E Lhotel
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - L Keller
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Frontzek
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - S C Capelli
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - O Zaharko
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P A McClarty
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, 01187 Dresden, Germany
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
| | - P Henelius
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Bovo L, Twengström M, Petrenko OA, Fennell T, Gingras MJP, Bramwell ST, Henelius P. Special temperatures in frustrated ferromagnets. Nat Commun 2018; 9:1999. [PMID: 29784922 PMCID: PMC5962592 DOI: 10.1038/s41467-018-04297-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 04/18/2018] [Indexed: 11/13/2022] Open
Abstract
The description and detection of unconventional magnetic states, such as spin liquids, is a recurring topic in condensed matter physics. While much of the efforts have traditionally been directed at geometrically frustrated antiferromagnets, recent studies reveal that systems featuring competing antiferromagnetic and ferromagnetic interactions are also promising candidate materials. We find that this competition leads to the notion of special temperatures, analogous to those of gases, at which the competing interactions balance, and the system is quasi-ideal. Although induced by weak perturbing interactions, these special temperatures are surprisingly high and constitute an accessible experimental diagnostic of eventual order or spin-liquid properties. The well characterised Hamiltonian and extended low-temperature susceptibility measurement of the canonical frustrated ferromagnet Dy2Ti2O7 enables us to formulate both a phenomenological and microscopic theory of special temperatures for magnets. Other members of this class of magnets include kapellasite Cu3Zn(OH)6Cl2 and the spinel GeCo2O4. Competing interactions in frustrated magnets give rise to complex emergent phenomena, which challenge a full microscopic understanding but invite comparison to other systems. Bovo et al. find an analogy to classical gases and identify special temperatures that reveal fine details of the microscopic Hamiltonian.
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Affiliation(s)
- L Bovo
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, UK.,Department of Innovation and Enterprise, University College London, 90 Tottenham Court Rd, Fitzrovia, London, W1T 4TJ, UK
| | - M Twengström
- Department of Physics, Royal Institute of Technology, SE-106 91, Stockholm, Sweden.
| | - O A Petrenko
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
| | - M J P Gingras
- Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.,Canadian Institute for Advanced Research, 180 Dundas St. W., Toronto, ON, M5G 1Z8, Canada.,Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON, N2L 2Y5, Canada
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, UK
| | - P Henelius
- Department of Physics, Royal Institute of Technology, SE-106 91, Stockholm, Sweden
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Gao S, Zaharko O, Tsurkan V, Prodan L, Riordan E, Lago J, Fåk B, Wildes AR, Koza MM, Ritter C, Fouquet P, Keller L, Canévet E, Medarde M, Blomgren J, Johansson C, Giblin SR, Vrtnik S, Luzar J, Loidl A, Rüegg C, Fennell T. Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr_{2}X_{4} (X=Se, S). Phys Rev Lett 2018; 120:137201. [PMID: 29694199 DOI: 10.1103/physrevlett.120.137201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Indexed: 06/08/2023]
Abstract
Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr_{2}Se_{4} is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy_{2}Ti_{2}O_{7}. In this Letter we use diffuse neutron scattering to show that both CdEr_{2}Se_{4} and CdEr_{2}S_{4} support a dipolar spin ice state-the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy_{2}Ti_{2}O_{7}, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er^{3+} ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr_{2}X_{4} (X=Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr_{2}X_{4} offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.
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Affiliation(s)
- Shang Gao
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland
| | - O Zaharko
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - V Tsurkan
- Experimental Physics V, University of Augsburg, D-86135 Augsburg, Germany
- Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova
| | - L Prodan
- Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova
| | - E Riordan
- School of Physics and Astronomy, Cardiff University, CF24 3AA Cardiff, United Kingdom
| | - J Lago
- Department of Inorganic Chemistry, Universidad del País Vasco (UPV-EHU), 48080 Bilbao, Spain
| | - B Fåk
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - A R Wildes
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - M M Koza
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - C Ritter
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - P Fouquet
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - L Keller
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - E Canévet
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
| | - M Medarde
- Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J Blomgren
- RISE Acreo AB, SE-411 33 Göteborg, Sweden
| | | | - S R Giblin
- School of Physics and Astronomy, Cardiff University, CF24 3AA Cardiff, United Kingdom
| | - S Vrtnik
- Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - J Luzar
- Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - A Loidl
- Experimental Physics V, University of Augsburg, D-86135 Augsburg, Germany
| | - Ch Rüegg
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Babkevich P, Katukuri VM, Fåk B, Rols S, Fennell T, Pajić D, Tanaka H, Pardini T, Singh RRP, Mitrushchenkov A, Yazyev OV, Rønnow HM. Magnetic Excitations and Electronic Interactions in Sr_{2}CuTeO_{6}: A Spin-1/2 Square Lattice Heisenberg Antiferromagnet. Phys Rev Lett 2016; 117:237203. [PMID: 27982654 DOI: 10.1103/physrevlett.117.237203] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Indexed: 06/06/2023]
Abstract
Sr_{2}CuTeO_{6} presents an opportunity for exploring low-dimensional magnetism on a square lattice of S=1/2 Cu^{2+} ions. We employ ab initio multireference configuration interaction calculations to unravel the Cu^{2+} electronic structure and to evaluate exchange interactions in Sr_{2}CuTeO_{6}. The latter results are validated by inelastic neutron scattering using linear spin-wave theory and series-expansion corrections for quantum effects to extract true coupling parameters. Using this methodology, which is quite general, we demonstrate that Sr_{2}CuTeO_{6} is an almost ideal realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV.
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Affiliation(s)
- P Babkevich
- Laboratory for Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Vamshi M Katukuri
- Chair of Computational Condensed Matter Physics, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - B Fåk
- Institut Laue-Langevin, CS 20156, F-38042 Grenoble Cedex 9, France
| | - S Rols
- Institut Laue-Langevin, CS 20156, F-38042 Grenoble Cedex 9, France
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - D Pajić
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, HR-10000 Zagreb, Croatia
| | - H Tanaka
- Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
| | - T Pardini
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - R R P Singh
- Department of Physics, University of California, Davis, California 95616, USA
| | - A Mitrushchenkov
- Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, Université Paris-Est, 5 boulevard Descartes, 77454 Marne-la-Vallée, France
| | - O V Yazyev
- Chair of Computational Condensed Matter Physics, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - H M Rønnow
- Laboratory for Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Maitra R, Fulp A, Snyder R, Fennell T, Bortoff K, Zhang Y. P-16INHIBITION OF ALCOHOLIC STEATOSIS BY A TYPE 1 CANNABINOID RECEPTOR ANTAGONIST. Alcohol Alcohol 2015. [DOI: 10.1093/alcalc/agv080.16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Fennell T, Kenzelmann M, Roessli B, Mutka H, Ollivier J, Ruminy M, Stuhr U, Zaharko O, Bovo L, Cervellino A, Haas MK, Cava RJ. Magnetoelastic excitations in the pyrochlore spin liquid Tb2Ti2O7. Phys Rev Lett 2014; 112:017203. [PMID: 24483925 DOI: 10.1103/physrevlett.112.017203] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Indexed: 06/03/2023]
Abstract
At low temperatures, Tb2Ti2O7 enters a spin liquid state, despite expectations of magnetic order and/or a structural distortion. Using neutron scattering, we have discovered that in this spin liquid state an excited crystal field level is coupled to a transverse acoustic phonon, forming a hybrid excitation. Magnetic and phononlike branches with identical dispersion relations can be identified, and the hybridization vanishes in the paramagnetic state. We suggest that Tb2Ti2O7 is aptly named a "magnetoelastic spin liquid" and that the hybridization of the excitations suppresses both magnetic ordering and the structural distortion. The spin liquid phase of Tb2Ti2O7 can now be regarded as a Coulomb phase with propagating bosonic spin excitations.
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Affiliation(s)
- T Fennell
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - M Kenzelmann
- Laboratory for Developments and Methods, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - B Roessli
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - H Mutka
- Institut Laue Langevin, BP 156, 6, rue Jules Horowitz, 38042 Grenoble Cedex 9, France
| | - J Ollivier
- Institut Laue Langevin, BP 156, 6, rue Jules Horowitz, 38042 Grenoble Cedex 9, France
| | - M Ruminy
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - U Stuhr
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - O Zaharko
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - L Bovo
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - A Cervellino
- Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - M K Haas
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
| | - R J Cava
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
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Calder S, Giblin SR, Parker DR, Deen PP, Ritter C, Stewart JR, Rols S, Fennell T. Neutron scattering and μSR investigations of the low temperature state of LuCuGaO₄. J Phys Condens Matter 2013; 25:356002. [PMID: 23917326 DOI: 10.1088/0953-8984/25/35/356002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
LuCuGaO₄ has magnetic Cu(2+) and diamagnetic Ga(3+) ions distributed on a triangular bilayer and is suggested to undergo a spin glass transition at Tg ∼ 0.4 K. Using μSR (muon spin rotation) and neutron scattering measurements, we show that at low temperature the spins form a short range correlated state with spin fluctuations detectable over a wide range of timescales: at 0.05 K magnetic fluctuations can be detected in both the μSR time window and also extending beyond 7 meV in the inelastic neutron scattering response, indicating magnetic fluctuations spanning timescales between ∼10(-5) and ∼10(-10) s. The dynamical susceptibility scales according to the form χ″(ω)T(α), with α = 1, throughout the measured temperature range (0.05-50 K). These effects are associated with quantum fluctuations and some degree of structural disorder in ostensibly quite different materials, including certain heavy fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond glasses. We therefore suggest that LuCuGaO₄ is an interesting model compound for the further examination of disorder and quantum magnetism.
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Affiliation(s)
- S Calder
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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Fennell T, Kenzelmann M, Roessli B, Haas MK, Cava RJ. Power-law spin correlations in the pyrochlore antiferromagnet Tb(2)Ti(2)O(7). Phys Rev Lett 2012; 109:017201. [PMID: 23031127 DOI: 10.1103/physrevlett.109.017201] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 03/19/2012] [Indexed: 06/01/2023]
Abstract
We investigate the low-temperature state of the rare-earth pyrochlore Tb(2)Ti(2)O(7) using polarized neutron scattering. Tb(2)Ti(2)O(7) is often described as an antiferromagnetic spin liquid with spin correlations extending over lengths comparable to individual tetrahedra of the pyrochlore lattice. We confirm this picture at 20 K but find that at 0.05 K the data contain evidence of pinch-point scattering, suggesting that the low temperature state of Tb(2)Ti(2)O(7) has power-law spin correlations.
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Affiliation(s)
- T Fennell
- Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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10
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Abstract
Spangolite, Cu(6)Al(SO(4))(OH)(12)Cl·3H(2)O, is a hydrated layered copper sulfate mineral. The Cu(2+) ions of each layer form a systematically depleted triangular lattice which approximates a maple leaf lattice. We present details of the crystal structure, which suggest that in spangolite this lattice actually comprises two species of edge linked trimers with different exchange parameters. However, magnetic susceptibility measurements show that despite the structural trimers, the magnetic properties are dominated by dimerization. The high temperature magnetic moment is strongly reduced below that expected for the six s = 1/2 in the unit cell.
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Affiliation(s)
- T Fennell
- Institut Laue Langevin, BP 156, 6, rue Jules Horowitz, 38042, Grenoble Cedex 9, France.
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Reid R, Muslimani A, Downing L, Wills SM, Fennell T, Marples B, Decker D. Expression of CD24 and CD44 tumor cells in breast cancer patients who received neoadjuvant therapy. J Clin Oncol 2010. [DOI: 10.1200/jco.2010.28.15_suppl.e21051] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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12
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Calder S, Fennell T, Kockelmann W, Lau GC, Cava RJ, Bramwell ST. Neutron scattering and crystal field studies of the rare earth double perovskite Ba2ErSbO6. J Phys Condens Matter 2010; 22:116007. [PMID: 21389482 DOI: 10.1088/0953-8984/22/11/116007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The rare earth double perovskite Ba(2)ErSbO(6) contains an ordered face-centred cubic lattice of Er(3+) ions, suggesting that this material is a candidate for showing the effects of geometric magnetic frustration. Crystal field effects have also been shown to be important in this series. We report a systematic experimental study involving neutron scattering and bulk measurements that show no evidence of long ranged magnetic order or spin glass freezing down to 70 mK. A description of the system in terms of a crystal field scheme is established from inelastic neutron scattering. These measurements rule out significant magnetic coupling and show that all observed properties are fully explained by a model of uncoupled magnetic Er(3+) ions.
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Affiliation(s)
- S Calder
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.
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Dalle-Ferrier C, Simon S, Zheng W, Badrinarayanan P, Fennell T, Frick B, Zanotti JM, Alba-Simionesco C. Consequence of excess configurational entropy on fragility: the case of a polymer-oligomer blend. Phys Rev Lett 2009; 103:185702. [PMID: 19905814 DOI: 10.1103/physrevlett.103.185702] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Indexed: 05/28/2023]
Abstract
By taking advantage of the molecular weight dependence of the glass transition of polymers and their ability to form perfectly miscible blends, we propose a way to modify the fragility of a system, from fragile to strong, keeping the same glass properties, i.e., vibrational density of states, mean-square displacement, and local structure. Both slow and fast dynamics are investigated by calorimetry and neutron scattering in an athermal polystyrene-oligomer blend, and compared to those of a pure 17-mer polystyrene considered to be a reference, of the same Tg. Whereas the blend and the pure 17-mer have the same heat capacity in the glass and in the liquid, their fragilities differ strongly. Thus, the difference in fragility is related to an extra configurational entropy created by the mixing process and acting at a scale much larger than the interchain distance, without affecting the fast dynamics and the structure of the glass.
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Affiliation(s)
- C Dalle-Ferrier
- Laboratoire de Chimie Physique, UMR 8000, Bâtiment 349, Université, Paris-Sud, 91405 Orsay, France
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Fennell T, Deen PP, Wildes AR, Schmalzl K, Prabhakaran D, Boothroyd AT, Aldus RJ, McMorrow DF, Bramwell ST. Magnetic Coulomb phase in the spin ice Ho2Ti2O7. Science 2009; 326:415-7. [PMID: 19729619 DOI: 10.1126/science.1177582] [Citation(s) in RCA: 443] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Spin-ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Their low-temperature magnetic state has been predicted to be a phase that obeys a Gauss' law and supports magnetic monopole excitations: in short, a Coulomb phase. We used polarized neutron scattering to show that the spin-ice material Ho2Ti2O7 exhibits an almost perfect Coulomb phase. Our result proves the existence of such phases in magnetic materials and strongly supports the magnetic monopole theory of spin ice.
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Affiliation(s)
- T Fennell
- Institut Laue-Langevin, Grenoble 38042, France.
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15
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Comstock CH, Lee W, Bronsteen RA, Fennell T. Rupture of the fetal abdomen in prune belly syndrome. Ultrasound Obstet Gynecol 2009; 33:487-488. [PMID: 19306470 DOI: 10.1002/uog.6341] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
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16
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Giblin SR, Champion JDM, Zhou HD, Wiebe CR, Gardner JS, Terry I, Calder S, Fennell T, Bramwell ST. Static magnetic order in Tb2Sn2O7 revealed by muon spin relaxation with exterior muon implantation. Phys Rev Lett 2008; 101:237201. [PMID: 19113586 DOI: 10.1103/physrevlett.101.237201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Revised: 10/16/2008] [Indexed: 05/27/2023]
Abstract
Tb2Sn2O7 has been proposed as an ordered spin ice, but the precise nature of the low temperature magnetic state remains uncertain. Recent independent muon spin relaxation (microSR) investigations suggest the possibility of exotic ground states with static order precluded on time scales longer than 10(-6) s. Here the more conventional hypothesis of canted ferromagnetism is tested by means of microSR with the muons stopped outside the sample, as well as ultralow field bulk magnetization measurements. The field cooled state shows conventional static order, while the zero field cooled state may be interpreted in terms of conventional closed domains. These results rule out purely dynamical ground states and illustrate the value of exterior muon implantation as a complement to the conventional technique.
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Affiliation(s)
- S R Giblin
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom.
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Pasewicz A, Idziak D, Koloczek J, Kus P, Wrzalik R, Fennell T, Honkimäki V, Ratuszna A, Burian A. Pair correlation function analysis of 5-(4-hexadecyloxyphenyl)-10,15,20-tri(4-pyridyl)porphyrin and 5-(4-methoxycarbonylphenyl)-10,15,20-tri(4-pyridyl)porphyrin. J Mol Struct 2008. [DOI: 10.1016/j.molstruc.2007.04.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Idziak D, Pasewicz A, Kołoczek J, Kuś P, Wrzalik R, Fennell T, Honkimäki V, Ratuszna A, Burian A. Molecular structure of 5,10,15,20-tetra(1-naphthyl)porphyrin and 5,10-di(4-hexadecyloxyphenyl)-15,20-di(4-pyridyl)porphyrin studied by high-energy X-ray diffraction. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.07.050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Cullen JP, Meehan C, O'Grady M, Fennell T, Lane SJ. The implementation of a nurse-provided, ward-based bilevel non-invasive ventilation service. Ir Med J 2005; 98:80-3. [PMID: 15869065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Bilevel non-invasive ventilation (NIV) is now standard of care for patients with acute hypercapnic respiratory failure (AHRF), and has an increasing role to play in patients with stable chronic hypercapnic respiratory failure (CHRF). The institution of an NIV service in a hospital setting requires major infrastructural and multidisciplinary input to be effective. This paper describes our experiences in setting up a 24-hour, nurse-provided, ward-based NIV service in a new acute teaching hospital in Dublin over a 39-month period. In addition, we provide audit data on 78 patients with AHRF treated with NIV by this service over this time period. The majority of patients (65) had their respiratory acidosis corrected and were discharged home; 11 patients failed NIV and were intubated and mechanically ventilated in the ITU; 13 patients died, 8 from respiratory causes and 5 from non-respiratory causes, indicating the critical nature of this condition.
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Affiliation(s)
- J P Cullen
- Department of Respiratory Medicine, Adelaicine & Meath Hospital, Tallaght, Dubin, Ireland
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20
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Bramwell ST, Harris MJ, den Hertog BC, Gingras MJ, Gardner JS, McMorrow DF, Wildes AR, Cornelius AL, Champion JD, Melko RG, Fennell T. Spin correlations in Ho2Ti2O7: a dipolar spin ice system. Phys Rev Lett 2001; 87:047205. [PMID: 11461643 DOI: 10.1103/physrevlett.87.047205] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2001] [Indexed: 05/23/2023]
Abstract
The pyrochlore material Ho2Ti2O7 has been suggested to show "spin ice" behavior. We present neutron scattering and specific heat results that establish unambiguously that Ho2Ti2O7 exhibits spin ice correlations at low temperature. Diffuse magnetic neutron scattering is quite well described by a nearest neighbor spin ice model and very accurately described by a dipolar spin ice model. The heat capacity is well accounted for by the sum of a dipolar spin ice contribution and an expected nuclear spin contribution, known to exist in other Ho3+ salts. These results settle the question of the nature of the low temperature spin correlations in Ho2Ti2O7 for which contradictory claims have been made.
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Affiliation(s)
- S T Bramwell
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, United Kingdom
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Calleman CJ, Wu Y, He F, Tian G, Bergmark E, Zhang S, Deng H, Wang Y, Crofton KM, Fennell T. Relationships between biomarkers of exposure and neurological effects in a group of workers exposed to acrylamide. Toxicol Appl Pharmacol 1994; 126:361-71. [PMID: 8209389 DOI: 10.1006/taap.1994.1127] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A study was performed among 41 workers heavily exposed to a mixture of acrylamide and acrylonitrile in the city of Xinxiang, Henan province, People's Republic of China. The workers underwent a complete medical and neurological examination and provided blood and urine for the determination of several biomarkers of exposure. Among the exposed workers, signs and symptoms indicating peripheral neuropathy were found with statistically significant increased frequencies compared to a group of controls from the same city. Based on neuropathic signs and symptoms and quantifiable indicators of peripheral nervous dysfunction, such as vibration thresholds and electroneuromyography measurements, a neurotoxicity index (NIn) specific for acrylamide-induced peripheral neuropathy was designed. The NIn, which adequately predicted the clinical diagnosis of peripheral neuropathy, was significantly correlated with the levels of mercapturic acids in 24-hr urine, hemoglobin adducts of acrylamide, accumulated in vivo doses of acrylamide, employment time, and vibration sensitivity. The NIn was correlated also with hemoglobin adducts of acrylonitrile, which was explained primarily by a correlation between acrylamide and acrylonitrile exposure in this workshop. However, it was not significantly correlated with momentary measures of exposure such as concentrations of acrylamide in the air or in the plasma of exposed workers. This study is the first in which adduct monitoring has been applied to the same group of individuals in which adverse health effects have been observed. The results seem to indicate that hemoglobin adducts are useful as predictors of acrylamide-induced peripheral neuropathy and that measurements of vibration thresholds are useful for identifying early neurotoxic effects in workplaces with hazardous exposures to acrylamide.
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Affiliation(s)
- C J Calleman
- Department of Environmental Health, University of Washington, Seattle 98195
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