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Matsuda M, Dissanayake SE, Abernathy DL, Qiu Y, Copley JRD, Kumada N, Azuma M. Frustrated magnetic interactions in an S = 3/2 bilayer honeycomb lattice compound Bi 3Mn 4O 12(NO 3). Phys Rev B 2019; 100:10.1103/physrevb.100.134430. [PMID: 33644522 PMCID: PMC7905988 DOI: 10.1103/physrevb.100.134430] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
An inelastic neutron scattering study has been performed in an S = 3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long-range magnetic order exists. In the magnetic-field-induced long-range ordered state at 10 T, the magnetic dispersions become slightly more intense, albeit still broad as in the disordered state, and two excitation gaps, probably originating from an easy-plane magnetic anisotropy and intrabilayer interactions, develop. Analyzing the magnetic dispersions using the linear spin-wave theory, we estimated the intraplane and intrabilayer magnetic interactions, which are almost consistent with those determined by ab initio density functional theory calculations [M. Alaei et al., Phys. Rev. B 96, 140404(R) (2017)], except the third and fourth neighbor intrabilayer interactions. Most importantly, as predicted by the theory, there is no significant frustration in the honeycomb plane but frustrating intrabilayer interactions probably give rise to the disordered ground state.
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Affiliation(s)
- M Matsuda
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - S E Dissanayake
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - D L Abernathy
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Y Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J R D Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - N Kumada
- Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae, Kofu 400-8511, Japan
| | - M Azuma
- Laboratory for Materials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan
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Bertrand CE, Self JL, Copley JRD, Faraone A. Nanoscopic length scale dependence of hydrogen bonded molecular associates' dynamics in methanol. J Chem Phys 2017; 146:194501. [PMID: 28527447 PMCID: PMC5648548 DOI: 10.1063/1.4983179] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Accepted: 04/25/2017] [Indexed: 11/14/2022] Open
Abstract
In a recent paper [C. E. Bertrand et al., J. Chem. Phys. 145, 014502 (2016)], we have shown that the collective dynamics of methanol shows a fast relaxation process related to the standard density-fluctuation heat mode and a slow non-Fickian mode originating from the hydrogen bonded molecular associates. Here we report on the length scale dependence of this slow relaxation process. Using quasielastic neutron scattering and molecular dynamics simulations, we show that the dynamics of the slow process is affected by the structuring of the associates, which is accessible through polarized neutron diffraction experiments. Using a series of partially deuterated samples, the dynamics of the associates is investigated and is found to have a similar time scale to the lifetime of hydrogen bonding in the system. Both the structural relaxation and the dynamics of the associates are thermally activated by the breaking of hydrogen bonding.
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Affiliation(s)
- C E Bertrand
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J L Self
- McKetta Department of Chemical Engineering, University of Texas, Austin, Texas 78712, USA
| | - J R D Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - A Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Affiliation(s)
- J. R. D. Copley
- National Institute of Standards and Technology Materials Science and Engineering Laboratory Gaithersburg, Maryland 20899
| | - D. F. R. Mildner
- National Institute of Standards and Technology Chemical Science and Technology Laboratory Gaithersburg, Maryland 20899
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Wen JJ, Koohpayeh SM, Ross KA, Trump BA, McQueen TM, Kimura K, Nakatsuji S, Qiu Y, Pajerowski DM, Copley JRD, Broholm CL. Disordered Route to the Coulomb Quantum Spin Liquid: Random Transverse Fields on Spin Ice in Pr_{2}Zr_{2}O_{7}. Phys Rev Lett 2017; 118:107206. [PMID: 28339241 DOI: 10.1103/physrevlett.118.107206] [Citation(s) in RCA: 6] [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: 09/27/2016] [Indexed: 06/06/2023]
Abstract
Inelastic neutron scattering reveals a broad continuum of excitations in Pr_{2}Zr_{2}O_{7}, the temperature and magnetic field dependence of which indicate a continuous distribution of quenched transverse fields (Δ) acting on the non-Kramers Pr^{3+} crystal field ground state doublets. Spin-ice correlations are apparent within 0.2 meV of the Zeeman energy. A random phase approximation provides an excellent account of the data with a transverse field distribution ρ(Δ)∝(Δ^{2}+Γ^{2})^{-1}, where Γ=0.27(1) meV. Established during high temperature synthesis due to an underlying structural instability, it appears disorder in Pr_{2}Zr_{2}O_{7} actually induces a quantum spin liquid.
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Affiliation(s)
- J-J Wen
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - S M Koohpayeh
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - K A Ross
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - B A Trump
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - T M McQueen
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - K Kimura
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan
- Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - S Nakatsuji
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan
- CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Y Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - D M Pajerowski
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J R D Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - C L Broholm
- Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
- Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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5
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Bertrand CE, Self JL, Copley JRD, Faraone A. Erratum: "Dynamic signature of molecular association in methanol" [J. Chem. Phys. 145, 014502 (2016)]. J Chem Phys 2017; 146:059901. [PMID: 28178797 DOI: 10.1063/1.4975774] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- C E Bertrand
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J L Self
- McKetta Department of Chemical Engineering, University of Texas, Austin, Texas 78712, USA
| | - J R D Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - A Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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6
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Affiliation(s)
- C. E. Bertrand
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J. L. Self
- McKetta Department of Chemical Engineering, University of Texas, Austin, Texas 78712, USA
| | - J. R. D. Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - A. Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Wu LS, Gannon WJ, Zaliznyak IA, Tsvelik AM, Brockmann M, Caux JS, Kim MS, Qiu Y, Copley JRD, Ehlers G, Podlesnyak A, Aronson MC. Orbital-exchange and fractional quantum number excitations in an f-electron metal, Yb2Pt2Pb. Science 2016; 352:1206-10. [DOI: 10.1126/science.aaf0981] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 04/29/2016] [Indexed: 11/02/2022]
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Ross KA, Qiu Y, Copley JRD, Dabkowska HA, Gaulin BD. Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7. Phys Rev Lett 2014; 112:057201. [PMID: 24580625 DOI: 10.1103/physrevlett.112.057201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Indexed: 06/03/2023]
Abstract
The recent determination of a robust spin Hamiltonian for the antiferromagnetic XY pyrochlore Er2Ti2O7 reveals a most convincing case of the "Order-by-Quantum-Disorder" mechanism for ground state selection. This mechanism relies on quantum fluctuations to remove an accidental symmetry of the magnetic ground state, and selects a particular ordered spin structure below TN=1.2 K. The removal of the continuous degeneracy results in an energy gap in the spectrum of spin wave excitations, long wavelength pseudo-Goldstone modes. We have measured the Order-by-Quantum-Disorder spin wave gap at a zone center in Er2Ti2O7, using low incident energy neutrons and the time-of-flight inelastic scattering method. We report a gap of Δ=0.053±0.006 meV, which is consistent with upper bounds placed on it from heat capacity measurements and roughly consistent with the theoretical estimate of ∼0.02 meV, further validating the spin Hamiltonian that led to that prediction. The gap is observed to vary with the square of the order parameter, and goes to zero for T∼TN.
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Affiliation(s)
- K A Ross
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA and NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Y Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
| | - J R D Copley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - H A Dabkowska
- Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - B D Gaulin
- Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1, Canada and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada and Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, Ontario M5G 1Z8, Canada
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9
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Zhou HD, Xu C, Hallas AM, Silverstein HJ, Wiebe CR, Umegaki I, Yan JQ, Murphy TP, Park JH, Qiu Y, Copley JRD, Gardner JS, Takano Y. Successive phase transitions and extended spin-excitation continuum in the S=1/2 triangular-lattice antiferromagnet Ba3CoSb2O9. Phys Rev Lett 2012; 109:267206. [PMID: 23368612 DOI: 10.1103/physrevlett.109.267206] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Indexed: 06/01/2023]
Abstract
Using magnetic, thermal, and neutron measurements on single-crystal samples, we show that Ba3CoSb2O9 is a spin-1/2 triangular-lattice antiferromagnet with the c axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the c axis. A pronounced extensive neutron-scattering continuum above spin-wave excitations, observed below T(N), implies that the system is in close proximity to one of two spin-liquid states that have been predicted for a 2D triangular lattice.
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Affiliation(s)
- H D Zhou
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA.
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Zhou HD, Choi ES, Li G, Balicas L, Wiebe CR, Qiu Y, Copley JRD, Gardner JS. Spin liquid state in the S = 1/2 triangular lattice Ba3CuSb2O9. Phys Rev Lett 2011; 106:147204. [PMID: 21561219 DOI: 10.1103/physrevlett.106.147204] [Citation(s) in RCA: 19] [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: 10/12/2010] [Indexed: 05/30/2023]
Abstract
The synthesis and characterization of Ba3CuSb2O9, which has a layered array of Cu2+ spins in a triangular lattice, are reported. The magnetic susceptibility and neutron scattering experiments of this material show no magnetic ordering down to 0.2 K with a θ(CW) = -55 K. The magnetic specific heat reveals a T-linear dependence with a γ = 43.4 mJ K(-2) mol(-1) below 1.4 K. These observations suggest that Ba3CuSb2O9 is a new quantum spin liquid candidate with a S = 1/2 triangular lattice.
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Affiliation(s)
- H D Zhou
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA.
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11
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Kamitakahara WA, Copley JRD, Cappelletti RL, Rush JJ, Neumann DA, Fischer JE, Mccauley JP, Smit AB. Rotations, Vibrations and Structure in Solid C60: Investigations by Neutron Scattering. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-270-167] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTIn a series of experiments on solid C60, the low-energy rotational dynamics of the molecules, the higher-energy vibrational spectra, and aspects of disorder in the static structure, have been studied. The nearly spherical shape of the C60 molecule, and the occurrence of an orientational phase transition at Tc=256 K, make the C60 solid an excellent system for investigations of orientational dynamics. Coherent quasi-elastic neutron scattering above Tc is described quantitatively by a rotational diffusion model. Below Tc, inelastic scattering froma soft librational mode is observed between 2 and 3 meV. Models of the strong, temperaturedependent diffuse scattering due to orientational disorder are discussed. Finally, measurements of the density of states for the intramolecular ( E ≥ 33 meV) vibrational modes are also presented.
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12
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Ross KA, Ruff JPC, Adams CP, Gardner JS, Dabkowska HA, Qiu Y, Copley JRD, Gaulin BD. Two-dimensional kagome correlations and field induced order in the ferromagnetic XY pyrochlore Yb2Ti2O7. Phys Rev Lett 2009; 103:227202. [PMID: 20366123 DOI: 10.1103/physrevlett.103.227202] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Indexed: 05/29/2023]
Abstract
Neutron scattering measurements show the ferromagnetic XY pyrochlore Yb2Ti2O7 to display strong quasi-two-dimensional (2D) spin correlations at low temperature, which give way to long range order (LRO) under the application of modest magnetic fields. Rods of scattering along 111 directions due to these 2D spin correlations imply a magnetic decomposition of the cubic pyrochlore system into decoupled kagome planes. A magnetic field of approximately 0.5 T applied along the [110] direction induces a transition to a 3D LRO state characterized by long-lived, dispersive spin waves. Our measurements map out a complex low temperature-field phase diagram for this exotic pyrochlore magnet.
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Affiliation(s)
- K A Ross
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
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13
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Janik JA, Zhou HD, Jo YJ, Balicas L, Macdougall GJ, Luke GM, Garrett JD, McClellan KJ, Bauer ED, Sarrao JL, Qiu Y, Copley JRD, Yamani Z, Buyers WJL, Wiebe CR. Itinerant spin excitations near the hidden order transition in URu(2)Si(2). J Phys Condens Matter 2009; 21:192202. [PMID: 21825472 DOI: 10.1088/0953-8984/21/19/192202] [Citation(s) in RCA: 3] [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] [Indexed: 05/31/2023]
Abstract
By means of neutron scattering we show that the high temperature precursor to the hidden order state of the heavy fermion superconductor URu(2)Si(2) exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of the long-lived longitudinal f spin excitations that appear below T(0). This suggests that there is a strongly hybridized character to the itinerant excitations observed previously above the hidden order transition. Here we present evidence that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets; hence the hidden order phase probably originates from a Fermi surface instability. We identify wavevectors that span nested regions of a f-d hybridized band calculation and that match the neutron spin crossover from incommensurate to commensurate on approach to the hidden order phase.
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Affiliation(s)
- J A Janik
- Department of Physics, Florida State University, Tallahassee, FL 32306-3016, USA. National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306-4005, USA
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Zhou HD, Wiebe CR, Jo YJ, Balicas L, Urbano RR, Lumata LL, Brooks JS, Kuhns PL, Reyes AP, Qiu Y, Copley JRD, Gardner JS. Chemical pressure induced spin freezing phase transition in kagome pr langasites. Phys Rev Lett 2009; 102:067203. [PMID: 19257628 DOI: 10.1103/physrevlett.102.067203] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2008] [Revised: 12/12/2008] [Indexed: 05/27/2023]
Abstract
The 2D kagome system Pr3Ga5SiO14 has been previously identified as a spin-liquid candidate in zero field, displaying no magnetic long-ranged order down to at least 35 mK. Perturbations upon such systems, either under applied fields or applied pressure, should induce a spin freezing phase transition, but there are very few experimental realizations of this phenomena other than the well-studied 3D pyrochlore Tb2Ti2O7. In this Letter, we report the observation of a spin freezing phase transition in Pr3Ga5SiO14 through the application of chemical pressure--that is, through a systematic substitution on the Si site with larger ions and an elongation of the nearest-neighbor Pr-Pr distance in the kagome lattice. This results in a suppression of the T2 component of the heat capacity, and the reduction of the exchange constant eventually leads to dipolar-driven spin freezing.
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Affiliation(s)
- H D Zhou
- Department of Physics, Florida State University, Tallahassee, Florida 32306-3016, USA
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Zhou HD, Wiebe CR, Janik JA, Balicas L, Yo YJ, Qiu Y, Copley JRD, Gardner JS. Dynamic spin ice: Pr2Sn2O7. Phys Rev Lett 2008; 101:227204. [PMID: 19113519 DOI: 10.1103/physrevlett.101.227204] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2008] [Indexed: 05/27/2023]
Abstract
In this Letter, we report a new spin ice--Pr2Sn2O7--which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin-ice model. However, these short-ranged ordered spins have a quasielastic response that is atypical of the canonical spin ices, and suggests that the ground state is dynamic (i.e., composed of locally ordered two-in-two-out spin configurations that can tunnel between energetically equivalent orientations). We report this as an example of a dynamic spin ice down to 200 mK.
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Affiliation(s)
- H D Zhou
- Department of Physics, Florida State University, Tallahassee, Florida 32306-3016, USA
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16
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Ruff JPC, Clancy JP, Bourque A, White MA, Ramazanoglu M, Gardner JS, Qiu Y, Copley JRD, Johnson MB, Dabkowska HA, Gaulin BD. Spin waves and quantum criticality in the frustrated XY pyrochlore antiferromagnet Er2Ti2O7. Phys Rev Lett 2008; 101:147205. [PMID: 18851568 DOI: 10.1103/physrevlett.101.147205] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Indexed: 05/26/2023]
Abstract
We report detailed measurements of the low temperature magnetic phase diagram of Er2Ti2O7. Heat capacity and time-of-flight neutron scattering studies of single crystals reveal unconventional low-energy states. Er3+ magnetic ions reside on a pyrochlore lattice in Er2Ti2O7, where local XY anisotropy and antiferromagnetic interactions give rise to a unique frustrated system. In zero field, the ground state exhibits coexisting short and long-range order, accompanied by soft collective spin excitations previously believed to be absent. The application of finite magnetic fields tunes the ground state continuously through a landscape of noncollinear phases, divided by a zero temperature phase transition at micro{0}H{c} approximately 1.5 T. The characteristic energy scale for spin fluctuations is seen to vanish at the critical point, as expected for a second order quantum phase transition driven by quantum fluctuations.
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Affiliation(s)
- J P C Ruff
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
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Zhou HD, Vogt BW, Janik JA, Jo YJ, Balicas L, Qiu Y, Copley JRD, Gardner JS, Wiebe CR. Partial field-induced magnetic order in the spin-liquid kagomé Nd3Ga5SiO14. Phys Rev Lett 2007; 99:236401. [PMID: 18233386 DOI: 10.1103/physrevlett.99.236401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2007] [Indexed: 05/25/2023]
Abstract
The distorted kagomé system Nd3Ga5SiO14 has been investigated with neutron scattering down to 0.046 K with no evidence of magnetic long range order of the Nd3+ moments in a zero field. Substantial diffuse scattering is observed which is in agreement with nearest-neighbor correlations between the fluctuating spins. Upon the application of a field in the c direction, the diffuse scattering is reduced in intensity while the magnetic Bragg peaks grow in intensity to saturate by 1 T to 1/2 of the expected magnetization. These measurements suggest that a unique spin-liquid state develops in Nd3Ga5SiO14 with a frustration index of f approximately |theta|/T_{C}> or =1300.
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Affiliation(s)
- H D Zhou
- Department of Physics, Florida State University, Tallahassee, Florida 32306-3016, USA
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18
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Carretta S, Santini P, Amoretti G, Guidi T, Copley JRD, Qiu Y, Caciuffo R, Timco G, Winpenny REP. Quantum oscillations of the total spin in a heterometallic antiferromagnetic ring: evidence from neutron spectroscopy. Phys Rev Lett 2007; 98:167401. [PMID: 17501458 DOI: 10.1103/physrevlett.98.167401] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Indexed: 05/15/2023]
Abstract
Using inelastic neutron scattering and applied fields up to 11.4 T, we have studied the spin dynamics of the Cr7Ni antiferromagnetic ring in the energy window 0.05-1.6 meV. We demonstrate that the external magnetic field induces an avoided crossing (anticrossing) between energy levels with different total-spin quantum numbers. This corresponds to quantum oscillations of the total spin of each molecule. The inelastic character of the observed excitation and the field dependence of its linewidth indicate that molecular spins oscillate coherently for a significant number of cycles. Precise signatures of the anticrossing are also found at higher energy, where measured and calculated spectra match very well.
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Affiliation(s)
- S Carretta
- Dipartimento di Fisica, Università di Parma, I-43100 Parma, Italy
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Enevoldsen AD, Hansen FY, Diama A, Taub H, Dimeo RM, Neumann DA, Copley JRD. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics. J Chem Phys 2007; 126:104704. [PMID: 17362078 DOI: 10.1063/1.2464092] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dynamics of monolayer films of the n-alkane tetracosane (n-C24H52) and the branched alkane squalane (C30H62) adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics (MD) simulations. Both molecules have 24 carbon atoms along their carbon backbone, and squalane has an additional six methyl side groups symmetrically placed along its length. The authors' principal objective has been to determine the influence of the side groups on the dynamics of the squalane monolayer and thereby assess its potential as a nanoscale lubricant. To investigate the dynamics of these monolayers they used both the disk chopper spectrometer (DCS) and the high flux backscattering spectrometer (HFBS) at the National Institute of Standards and Technology. These instruments made it possible to study dynamical processes such as molecular diffusive motions and vibrations on very different time scales: 1-40 ps (DCS) and 0.1-4 ns (HFBS). The MD simulations were done on corresponding time scales and were used to interpret the neutron spectra. The authors found that the dynamics of the two monolayers are qualitatively similar on the respective time scales and that there are only small quantitative differences that can be understood in terms of the different masses and moments of inertia of the two molecules. In the course of this study, the authors developed a procedure to separate out the low-frequency vibrational modes in the spectra, thereby facilitating an analysis of the quasielastic scattering. They conclude that there are no major differences in the monolayer dynamics caused by intramolecular branching. It remains to be seen whether this similarity in monolayer dynamics also holds for the lubricating properties of these molecules in confined geometries.
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Affiliation(s)
- A D Enevoldsen
- Department of Chemistry, Technical University of Denmark, IK 207 DTU, DK-2800 Lyngby, Denmark
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Rule KC, Ruff JPC, Gaulin BD, Dunsiger SR, Gardner JS, Clancy JP, Lewis MJ, Dabkowska HA, Mirebeau I, Manuel P, Qiu Y, Copley JRD. Field-induced order and spin waves in the pyrochlore antiferromagnet Tb2Ti207. Phys Rev Lett 2006; 96:177201. [PMID: 16712328 DOI: 10.1103/physrevlett.96.177201] [Citation(s) in RCA: 3] [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: 01/30/2006] [Indexed: 05/09/2023]
Abstract
High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of a magnetic field applied along [110]. In zero field at T = 0.4 K, Tb(2)Ti(2)0(7) is a highly correlated cooperative paramagnet with disordered spins residing on a pyrochlore lattice of corner-sharing tetrahedra. Application of a small field condenses much of the magnetic diffuse scattering, characteristic of the disordered spins, into a new Bragg peak characteristic of a polarized paramagnet. At higher fields, a magnetically ordered phase is induced, which supports spin wave excitations indicative of continuous, rather than Ising-like, spin degrees of freedom.
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Affiliation(s)
- K C Rule
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
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Phelan D, Louca D, Rosenkranz S, Lee SH, Qiu Y, Chupas PJ, Osborn R, Zheng H, Mitchell JF, Copley JRD, Sarrao JL, Moritomo Y. Nanomagnetic droplets and implications to orbital ordering in LA(1-x)Sr(x)CoO3. Phys Rev Lett 2006; 96:027201. [PMID: 16486622 DOI: 10.1103/physrevlett.96.027201] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Indexed: 05/06/2023]
Abstract
Inelastic cold-neutron scattering on LaCoO3 provided evidence for a distinct low energy excitation at 0.6 meV coincident with the thermally induced magnetic transition. Coexisting strong ferromagnetic (FM) and weaker antiferromagnetic correlations that are dynamic follow the activation to the excited state, identified as the intermediate S = 1 spin triplet. This is indicative of dynamical orbital ordering favoring the observed magnetic interactions. With hole doping as in La(1-x)Sr(x)CoO3 , the FM correlations between Co spins become static and isotropically distributed due to the formation of FM droplets. The correlation length and condensation temperature of these droplets increase rapidly with metallicity due to the double exchange mechanism.
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Affiliation(s)
- D Phelan
- Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA
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Gaulin BD, Lee SH, Haravifard S, Castellan JP, Berlinsky AJ, Dabkowska HA, Qiu Y, Copley JRD. High-resolution study of spin excitations in the singlet ground state of SrCu2(BO3)2. Phys Rev Lett 2004; 93:267202. [PMID: 15698016 DOI: 10.1103/physrevlett.93.267202] [Citation(s) in RCA: 17] [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: 01/21/2004] [Indexed: 05/24/2023]
Abstract
High-resolution, inelastic neutron scattering measurements on SrCu2(BO3)2, a realization of the Shastry-Sutherland model for two-dimensional Heisenberg antiferromagnets, reveal the dispersion of the three single triplet excitations continuously across the (H,0) direction within its tetragonal basal plane. These measurements also show distinct Q dependencies for the single and multiple triplet excitations, and that these excitations are largely dispersionless perpendicular to this plane. The temperature dependence of the intensities of these excitations is well described as the complement of the dc susceptibility of SrCu2(BO3)2.
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Affiliation(s)
- B D Gaulin
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
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Faraone A, Liu L, Mou CY, Shih PC, Brown C, Copley JRD, Dimeo RM, Chen SH. Dynamics of supercooled water in mesoporous silica matrix MCM-48-S. Eur Phys J E Soft Matter 2003; 12 Suppl 1:S59-S62. [PMID: 15011017 DOI: 10.1140/epjed/e2003-01-015-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/01/2003] [Indexed: 05/24/2023]
Abstract
Using three different quasielastic neutron spectrometers with widely different resolutions, we have been able to study the microscopic translational and rotational dynamics of water, in a mesoporous silica matrix MCM-48-S, from T=300 K to 220 K, with a single consistent model. We formulated our fitting routine using the relaxing cage model. Thus, from the fit of the experimental data, we extracted the fraction of water bound to the surface of the pore, the characteristic relaxation times of the long-time translational and rotational decays, the stretch exponent describing the shape of the relaxation processes, and the power exponent determining the Q-dependence of the translational relaxation time. A tremendous slowing down of the rotational relaxation time, as compared to the translational one, has been observed.
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Affiliation(s)
- A Faraone
- Department of Nuclear Engineering, MIT, Cambridge, Massachusetts, USA
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Fratini E, Chen SH, Baglioni P, Cook JC, Copley JRD. Dynamic scaling of quasielastic neutron scattering spectra from interfacial water. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:010201. [PMID: 11800665 DOI: 10.1103/physreve.65.010201] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2001] [Indexed: 05/23/2023]
Abstract
A method for analysis of high-resolution quasielastic neutron scattering (QENS) spectra of water in porous media is proposed and applied to the case of water in hydrated tricalcium and dicalcium silicates. We plot the normalized frequency-dependent susceptibility as a function of a scaling variable [omega]/omega(p), where omega(p) is the peak position of the susceptibility function. QENS data have been scaled into a single master curve and fitted with an empirical formula proposed by Bergman to obtain three independent parameters describing the relaxation dynamics of hydration water in calcium silicates.
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Affiliation(s)
- E Fratini
- Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Dormann E, Copley JRD, Jaccarino V. Temperature dependence of the MnF2and KMnF3lattice parameters from room temperature to the melting point. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/10/15/012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Mizuki J, Copley JRD, Endoh Y, Ishikawa Y. A study of the magnetic phase diagram of the Cr-Si system near the tricritical point. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0305-4608/16/8/008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Lartigue C, Copley JRD, Mezei F, Springer T. Focusing of neutron beams using curved mirrors for small angle scattering. J of Neutron Res 1996. [DOI: 10.1080/10238169608200211] [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] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Michel KH, Copley JRD. Orientational fluctuations, diffuse scattering and orientational order in solid C 60. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396083274] [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: 11/10/2022] Open
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Neumann DA, Copley JRD, Kamitakahara WA, Rush JJ, Cappelletti RL, Coustel N, Fischer JE, McCauley JP, Smith AB, Creegan KM, Cox DM. Rotational dynamics and orientational melting of C60: A neutron scattering study. J Chem Phys 1992. [DOI: 10.1063/1.462876] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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