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| 2. |
- Argyriou, Dimitri
(author)
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Reinventing neutron science in Europe
- 2014
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In: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 13:8, s. 767-768
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Journal article (other academic/artistic)abstract
- Neutron science has been a remarkable success story for European research. For this to continue, scientists need to be prepared to forge new networks and technologies.
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| 3. |
- Artyukhin, Sergey, et al.
(author)
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Solitonic lattice and Yukawa forces in the rare-earth orthoferrite TbFeO3
- 2012
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In: Nature Materials. - 1476-4660. ; 11:8, s. 694-699
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Journal article (peer-reviewed)abstract
- The random fluctuations of spins give rise to many interesting physical phenomena, such as the 'order-from-disorder' arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340 angstrom at 3 K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei.
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| 4. |
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| 5. |
- Kanaki, Kalliopi, et al.
(author)
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Statistical Energy Determination in Neutron Detector Systems for Neutron Scattering Science
- 2012
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In: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC). - 1082-3654. ; , s. 162-166
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Conference paper (peer-reviewed)abstract
- This contribution evaluates the feasibility and potential of a statistical determination of the neutron energy for thermal and cold neutrons in the new generation of neutron detectors. For the European Spallation Source (ESS), sited in Lund, Sweden, which is planned to be operational in 2019, and the world's leading source for the study of materials with neutrons by 2025, novel neutron detectors represent a critical technology that needs to be developed. The discussion here is based upon B-10 based thin-film detectors for neutron scattering science; however such a development is generalisable to other converter materials and potentially relevant to applications outside of neutron scattering science.
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| 6. |
- Kimber, Simon A. J., et al.
(author)
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Charge Order at the Frontier between the Molecular and Solid States in Ba3NaRu2O9
- 2012
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In: Physical Review Letters. - 1079-7114. ; 108:21
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Journal article (peer-reviewed)abstract
- We show that the valence electrons of Ba3NaRu2O9, which has a quasimolecular structure, completely crystallize below 210 K. Using an extended Hubbard model, we show that the charge ordering instability results from long-range Coulomb interactions. However, orbital ordering, metal-metal bonding, and formation of a partial spin gap enforce the magnitude of the charge separation. The striped charge order and frustrated hcp lattice of Ru2O9 dimers lead to competition with a quasidegenerate charge-melted phase under photoexcitation at low temperature. Our results establish a broad class of simple metal oxides as models for emergent phenomena at the border between the molecular and solid states.
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| 7. |
- Kimber, Simon A. J., et al.
(author)
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Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV2O6
- 2011
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 84:10
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Journal article (peer-reviewed)abstract
- We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin-chain compound CoV2O6. Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to similar to 6T(N). Above T-N = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest-neighbor exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and T-N to a state with a 1/3 magnetization plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the antiferromagnetic state has incommensurate long-range order and inelastic time-of-flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above T-N, we find two broad bands between 3.5 and 5 meV and thermally activated low-energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform ferromagnetic Ising spin chain. Below T-N, we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below T-N, but above 5 K, is identified which may correspond to a crossover between two- and three-dimensional magnetic ordering.
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| 8. |
- Kimber, Simon A. J., et al.
(author)
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Valence bond liquid phase in the honeycomb lattice material Li2RuO3
- 2014
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 89:8
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Journal article (peer-reviewed)abstract
- The honeycomb lattice material Li2RuO3 undergoes a dimerization of Ru4+ cations on cooling below 270 degrees C, where the magnetic susceptibility vanishes. We use density functional theory calculations to show that this reflects the formation of a valence bond crystal, with a strong structural bond disproportionation. On warming, x-ray diffraction shows that discrete threefold symmetry is regained on average, and the dimerization apparently disappears. In contrast, local structural measurements using high-energy x rays show that disordered dimers survive at the nanoscale up to at least 650 degrees C. The high-temperature phase of Li2RuO3 is thus an example of a valence bond liquid, where thermal fluctuations drive resonance between different dimer coverages, a classic analog of the resonating valence bond state often discussed in connection with high-T-c cuprates.
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| 9. |
- Prokes, K., et al.
(author)
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Collapsed tetragonal phase in Ca(Fe1-xCox)(2)As-2 stabilized by pressure: Structural studies using single-crystal neutron diffraction
- 2012
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 85:10
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Journal article (peer-reviewed)abstract
- Ca(Fe1-xCox)(2)As-2 single crystals with concentration x = 0.032, 0.051, and 0.063 were investigated by means of neutron diffraction under hydrostatic pressure. The region of existence of the high-temperature tetragonal, low-temperature orthorhombic, and pressure-induced collapsed tetragonal phases have been determined and the corresponding p-T phase diagrams for the three compositions have been constructed. Structural details of the tetragonal phases at various conditions have been determined. The anomaly marking the orthorhombic-to-tetragonal structural phase transition temperature T-S decreases with increasing Co substitution. Similarly to that, the critical pressure of the tetragonal (or orthorhombic)-to-collapsed-tetragonal transition also decreases with increasing Co doping level. The behavior is highly hysteretic and the differences in critical pressures with increasing and decreasing branches eventually makes the collapsed tetragonal phase stable down to ambient pressure and enables structural studies under identical conditions. Within the error bars on the fourth digit, no modification of the As structural positional parameter is found. Such a result suggests that the change of the As-As bond is caused solely by the reduction of the c-axis lattice parameter.
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| 10. |
- Viskadourakis, Z., et al.
(author)
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Low-temperature ferroelectric phase and magnetoelectric coupling in underdoped La2CuO4+x
- 2012
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 85:21
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Journal article (peer-reviewed)abstract
- We report the discovery of ferroelectricity below 4.5 K in highly underdoped La2CuO4+x accompanied by slow charge dynamics which develop below T similar to 40 K. An anisotropic magnetoelectric response has also been observed, indicating considerable spin-charge coupling in this lightly doped parent high-temperature copper-oxide superconductor. The ferroelectric state is proposed to develop from polar nanoregions, in which spatial inversion symmetry is locally broken due to nonstoichiometric carrier doping.
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