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Browsing by Author "Yu, DH"

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Ab initio calculations as a quantitative tool in the inelastic neutron scattering study of a single-molecule magnet analogue
(Royal Society of Chemistry (RSC), 2016-02-04) Vonci, M; Giansiracusa, MJ; Gable, RW; Van den Heuvel, W; Latham, K; Moubaraki, B; Murray, KS; Yu, DH; Mole, RA; Soncini, A; Boskovic, C
Ab initio calculations carried out on the Tb analogue of the single-molecule magnet family Na9[Ln(W5O18)2] (Ln = Nd, Gd, Ho and Er) have allowed interpretation of the inelastic neutron scattering spectra. The combined experimental and theoretical approach sheds new light on the sensitivity of the electronic structure of the Tb(III) ground and excited states to small structural distortions from axial symmetry, thus revealing the subtle relationship between molecular geometry and magnetic properties of the two isostructural species that comprise the sample. © The Royal Society of Chemistry 2016.
Alumina template-assisted electrodeposition of Bi2Te2.7Se0.3 nanowire arrays
(Elsevier, 2010-06-01) Li, XL; Cai, KF; Li, H; Yu, DH; Wang, X; Wang, HF
Bi2Te2.7Se0.3 nanowire arrays have been fabricated by electrodeposition into the pores of an anodic aluminum oxide (AAO) template followed by annealing at 300°C under Ar atmosphere. The as-prepared nanowires were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The nanowires are uniform single crystalline with diameter of ~14 nm. © 2010, Elsevier Ltd.
Application of inelastic neutron scattering for thermoelectric materials study
(Australian Nuclear Science and Technology Organisation, 2021-11-25) Yu, DH
Research on thermoelectric (TE) materials have been an active field for the past decade as TE material can potentially be used in many niche areas such as to power space probe and convert waste-heat into electricity. Continuing developments are undergoing in the search for advanced TE materials that could play significant role in sustainable technology. One of the strategies in improving the performance of a thermoelectric material is to decrease the thermal conductivity, which is directly related to the lattice dynamics of the materials. Measurement of phonon density of states and phonon dispersion as a function of temperature can provide deep insight of the thermal conductivity in terms of, for example, anharmonic vibrations and low energy rattling modes. PELICAN, a time of fight neutron spectrometer at ACNS, has been actively used for such kind of studies. In this presentation, I will give a brief introduction and the current status of TE material research, followed by the link to material lattice dynamics and explore how inelastic neutron scattering can help in fundamental understanding of the thermoelectric properties with a couple of study cases. © 2021 The Author
Author Correction: A one-third magnetization plateau phase as evidence for the Kitaev interaction in a honeycomb-lattice antiferromagnet
(Springer Nature, 2023-09-10) Shangguan, Y; Bao, S; Dong, ZY; Xi, N; Gao, YP; Ma, Z; Wang, W; Qi, Z; Zhang, S; Huang, Z; Liao, J; Zhao, X; Zhang, B; Cheng, S; Xu, H; Yu, DH; Mole, RA; Murai, N; Ohira-Kawamura, S; He, LH; Hao, J; Yan, QB; Song, F; Li, W; Yu, SL; Li, JX; Wen, JS
Correction to: Nature Physics, published online 25 September 2023. In the version of the article initially published, the affiliation of Zhen Ma, now reading School of Materials Science and Engineering, Hubei Normal University, Huangshi, China, appeared incorrectly. This has been updated in the HTML and PDF versions of the article. n the version of the article initially published, the affiliation of Zhen Ma, now reading School of Materials Science and Engineering, Hubei Normal University, Huangshi, China, appeared incorrectly. This has been updated in the HTML and PDF versions of the article. © 2024 Springer Nature Limited.
Boson peak in ultrathin alumina layers investigated with neutron spectroscopy
(American Physical Society, 2020-06-11) Cortie, DL; Cyster, MJ; Ablott, TA; Richardson, C; Smith, JS; Iles, GN; Wang, XL; Mitchell, DRG; Mole, RA; de Souza, NR; Yu, DH; Cole, JH
Bulk glasses exhibit extra vibrational modes at low energies, collectively known as the boson peak. The vibrational dynamics in nanoscale alumina glasses have an impact on the performance of qubits and other superconducting devices; however, the frequency of the boson peak has not been previously measured. Here we report neutron spectroscopy experiments on Al/Al2O3 nanoparticles consisting of spherical metallic cores with a radii from 20 to 1000 nm surrounded by a 3.5-nm-thick alumina glass. A low-energy peak is observed at ωBP = 2.8 ± 0.6 meV for highly oxidized particles, indicating an excess in the density of states. The intensity of the peak scales inversely with particle size and oxide fraction, indicating a surface origin, and is redshifted by 3 meV with respect to the van Hove singularity of γ -phase Al2O3 nanocrystals. Molecular-dynamics simulations of α-Al2O3, γ -Al2O3 and α-Al2O3 show that the observed boson peak is a signature of the ultrathin glass surface and the characteristic frequency is reduced compared to the peak in the bulk glass. © 2020 The Authors. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license.
Characterisation and application of a SPLEED-based spin polarisation analyser
(Elsevier, 2007-12-15) Yu, DH; Math, C; Meier, M; Escher, M; Rangelov, G; Donath, M
A commercial electron spin analyser, based on spin-polarised low-energy electron diffraction (SPLEED) from W(100), has been characterised with incident polarised electron beams from a standard GaAs polarised electron source. The dependence of the Sherman function on the scattering energy and elapse time after CO-flash of the tungsten crystal of the analyser have been measured. The influence of the stray magnetic field on the performance of the analyser has been investigated. The spin analyser has been applied in monitoring the reorientation transition of the easy magnetisation direction of Fe films on W(110) upon the exposure of CO adsorbent on the surface. © 2007, Elsevier Ltd.
Collective nonlinear electric polarization via defect-driven local symmetry breaking
(Royal Society of Chemistry, 2019-05-17) Dong, W; Cortie, DL; Lu, T; Sun, QB; Narayanan, N; Hu, WB; Jacob, L; Li, Q; Yu, DH; Chen, H; Chen, AP; Wei, XY; Wang, G; Humphrey, MG; Frankcombe, TJ; Liu, Y
In this work, we report the defect-mediated, abnormal non-linear polarization behavior observed in centrosymmetric rutile TiO2 where less than 1 at% of sterically mismatched Mg2+ ions are introduced to create ferroelectric-like polarization hysteresis loops. It is found that the Image ID:c9mh00516a-t2.gif defect cluster produces a dipole moment exceeding 6 Debye, with a rotatable component. Such a polarization is further enhanced by the displacement of neighboring Ti4+ ions. The coupling between such defect-driven symmetry-breaking regions generates a collective nonlinear electrical polarization state that persists to high temperatures. More importantly, an observation of abnormal bias shift of polarization hysteresis suggests an antiparallel alignment of certain dipoles frozen relative to the external poling electric field, which is associated with oxygen vacancy hopping. This result challenges the long-standing notion of parallel alignment of dipoles with the external electric field in ferroelectrics. This work also reveals an unexpected new form of non-linear dielectric polarization (non-ferroelectricity) in solid-state materials. © Royal Society of Chemistry 2024
A colossal barocaloric effect induced by the creation of a high-pressure phase
(Royal Society of Chemistry (RSC), 2023-01-13) Zhang, Z; Jiang, X; Hattori, T; Xu, X; Li, M; Yu, CY; Zhang, Z; Yu, DH; Mole, RA; Yano, SI; Chen, J; He, LH; Wang, CW; Wang, H; Li, B; Zhang, ZD
As a promising environment-friendly alternative to current vapor-compression refrigeration, solid-state refrigeration based on the barocaloric effect has been attracting worldwide attention. Generally, both phases in which a barocaloric effect occurs are present at ambient pressure. Here, instead, we demonstrate that KPF6 exhibits a colossal barocaloric effect due to the creation of a high-pressure rhombohedral phase. The phase diagram is constructed based on pressure-dependent calorimetric, Raman scattering, and neutron diffraction measurements. The present study is expected to provide an alternative routine to colossal barocaloric effects through the creation of a high-pressure phase. © Royal Society of Chemistry 2024.
Competing itinerant and local spin interactions in kagome metal FeGe
(Springer Nature, 2024-03) Chen, LB; Teng, XO; Tan, HX; Winn, BL; Granroth, GE; Ye, F; Yu, DH; Mole, RA; Gao, B; Yan, BH; Yi, M; Dai, PC
The combination of a geometrically frustrated lattice, and similar energy scales between degrees of freedom endows two-dimensional Kagome metals with a rich array of quantum phases and renders them ideal for studying strong electron correlations and band topology. The Kagome metal, FeGe is a noted example of this, exhibiting A-type collinear antiferromagnetic (AFM) order at TN ≈ 400 K, then establishes a charge density wave (CDW) phase coupled with AFM ordered moment below TCDW ≈ 110 K, and finally forms a c-axis double cone AFM structure around TCanting ≈ 60 K. Here we use neutron scattering to demonstrate the presence of gapless incommensurate spin excitations associated with the double cone AFM structure of FeGe at temperatures well above TCanting and TCDW that merge into gapped commensurate spin waves from the A-type AFM order. Commensurate spin waves follow the Bose factor and fit the Heisenberg Hamiltonian, while the incommensurate spin excitations, emerging below TN where AFM order is commensurate, start to deviate from the Bose factor around TCDW, and peaks at TCanting. This is consistent with a critical scattering of a second order magnetic phase transition with decreasing temperature. By comparing these results with density functional theory calculations, we conclude that the incommensurate magnetic structure arises from the nested Fermi surfaces of itinerant electrons and the formation of a spin density wave order. © The Author(s) 2024 - Open Access CC 4.0
Cooling field tuned magnetic phase transition and exchange bias-like effect in Y0.9Pr0.1CrO3
(AIP Publishing, 2015-09-11) Deng, DM; Zheng, JS; Yu, DH; Wang, BM; Sun, DH; Avdeev, M; Feng, Z; Jing, C; Lu, B; Ren, W; Cao, SX; Zhang, JC
Cooling magnetic field dependence of magnetic phase transition has been observed in Y0.9Pr0.1CrO3. GzFx order (spin structure of PrCrO3) is dominant after zero field cooling (ZFC), whereas GxFz order (spin structure of YCrO3) is dominant after cooling under a field higher than 100 Oe. Positive/negative exchange bias-like effect, with large vertical shift and small horizontal shift, has been observed after FC/ZFC process. The vertical shift can be attributed to the frozen ordered Pr3+ and Cr3+ spins in magnetic domains, because of the strong coupling between Pr3+ and Cr3+ sublattices; while the horizontal shift is a result of the pinning of spins at the interfaces. The frozen structure is generated by the field used for the measurement of the initial magnetization curve of M(H) for the ZFC cooled sample, while it is generated by the cooling field for the sample cooled under a cooling field higher than 100 Oe. © 2015 AIP Publishing LLC.
Copper diffusion rates and hopping pathways in superionic Cu 2Se: implications for thermoelectricity
(SSRN, 2020-10-21) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DL
The ultra-low thermal conductivity of Cu2Se is well established, but there is so far no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron spectroscopy. Reasonable agreement was found between these approaches, consistent with the experimental coefficient of 3.1 ± 1.3 10-5 cm2.s-1 and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetragonal and interstitial octahedral sites. This process forms dynamic Frenkel defects, however, there is no indication of additional broadening in the density-of-states indicating the intrinsic anharmonic interactions dictate the phonon lifetimes. © Preprint article - 2023 Elsevier Inc.
Copper diffusion rates and hopping pathways in superionic Cu2Se
(Elsevier, 2021-08-15) Nazrul Islam, SMK; Mayank, P; Ouyang, Y; Chen, J; Sagotra, AK; Li, M; Cortie, MB; Mole, RA; Cazorla, C; Yu, DH; Wang, XL; Robinson, RA; Cortie, DL
The ultra-low thermal conductivity of Cu2Se is well established, but so far there is no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron scattering. Reasonable agreement was found between these approaches, consistent with a diffusion coefficient of 3.1 ± 1.3 x 10−5 cm2.s−1 at 675 K and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetrahedral and interstitial octahedral sites. This process forms dynamic Frenkel defects. Despite the latter processes, there is no major loss of the phonon mode intensity in the superionic state, and there is no strong correlation between the phonon spectra and the increased diffusion rates. Instead, intrinsic anharmonic phonon interactions appear to dictate the thermal conductivity above and below the superionic transition, and there is only subtle mode broadening associated with the monoclinic-cubic structural transition point, with the phonon density-of-states remaining almost constant at higher temperatures. © 2021 Acta Materialia Inc.
Critical role of the coupling between the octahedral rotation and a-site ionic displacements in PbZrO3-based antiferroelectric materials investigated by in situ neutron diffraction
(American Physical Society, 2017-12-21) Lu, T; Studer, AJ; Yu, DH; Withers, RL; Feng, Y; Chen, H; Islam, SS; Xu, Z; Liu, Y
This in situ neutron-diffraction study on antiferroelectric (AFE) Pb0.99(Nb0.02Zr0.65Sn0.28Ti0.05)O3 polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and A-site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and E-field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and A-site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples’ FE and AFE properties. ©2017 American Physical Society - Open access
Defect structure and property consequence when small Li+ ions meet BaTiO3
(American Physical Society, 2020-08-31) Narayanan, N; Lou, Q; Rawal, A; Lu, T; Liu, Z; Chen, J; Langley, J; Chen, H; Hester, JR; Cox, N; Fuess, H; McIntyre, GJ; Li, G; Yu, DH; Liu, Y
In the present work the longstanding issue of the structure and dynamics of smaller ions in oxides and its impact on the properties was investigated on 7% Li-doped BaTiO3. The investigation combined several techniques, notably neutron powder diffraction (NPD), nuclear magnetic resonance (7Li-NMR), electron paramagnetic resonance (EPR), electron microprobe, electric polarization (EP) measurement, and electronic structure calculations based on density-functional theory (DFT). Electron microprobe confirmed multiple phases, one containing incorporated Li in the BaTiO3 host lattice and another glassy phase which breaks the host lattice due to excessive Li accumulation. While the average structure of Li in BaTiO3 could not be determined by NPD, 7Li-NMR revealed one broad “disordered” and multiple “ordered” peaks. Local structure models with different defect types involving Li+ were modeled and the corresponding chemical shifts (δ) were compared with experimental values. It is found that the closest defect model describing the ordered peaks, is with Ti4+ being replaced by four Li+ ions. The biexponential behavior of the spin-lattice relaxation of the ordered peaks each with a short and a long relaxation discloses the existence of paramagnetic ions. Finally, EPR revealed the existence of the paramagnetic ion Ti3+ as a charge-transfer defect. DFT calculations disclosed local antipolar displacements of Ti ions around both types of defect sites upon insertion of Li+. This is in accordance with the experimental observation of pinching effects of the EP in Li-doped BaTiO3. These studies demonstrate the huge impact of the local structure of the doped smaller/lighter ions on the functional properties of oxides. ©2020 American Physical Society
Defect structure-property correlations in Li doped BaTiO3
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Narayanan, N; Lou, Q; Rawal, A; Lu, T; Liu, Z; Chen, J; Langley, J; Chen, H; Hester, JR; Cox, N; Fuess, H; McIntyre, GJ; Li, G; Yu, DH; Liu, Y; Li, G
In the present work we investigate the important issue of the structure and dynamics of smaller ions in oxides and the resulting impact on its functional properties. For this purpose, we selected a 7% Li-doped BaTiO3. Li is a vital ingredient in novel energy storage technologies such as Li-ion batteries. The smaller Li-ion can influence the structural stability, homogeneity, local environment, and dynamic behavior of the host lattice, affecting and optimizing the dielectric and multiferroic properties of novel polar functional materials [1-2]. However, the Li-ion positions and dynamics in functional materials are not completely understood, controversially discussed and are the subject of extensive ongoing research [3]. Furthermore, sample inhomogeneity due to Li migration to the grain boundary and/or development of multiple phases complicates the elucidation of the structure-property correlations that may lead to incorrect interpretations [4]. The selection of BaTiO3 as the host lattice is due to materials based on this being considered as the alternative to the piezoelectric lead zirconate titanate, citing environmental issues [5]. BaTiO3 also crystallizes in a simple perovskite structure and Li ions can be effectively doped into it at lower doping levels. Very recently, field-dependent electric polarization measurements on BaTiO3 exhibited a polarization–electric field double hysteresis loop upon Li doping [4]. These drastic changes to the electric polarization, related to the doping poses a good test case for the investigation of the Li induced defect structure model and its influence on the functional properties. To elucidate the above structure-property correlations, we combined several techniques, such as neutron powder diffraction electron microprobe associated with the wavelength-dispersive spectroscopy, 7Li nuclear magnetic resonance spectroscopy (NMR), electron paramagnetic resonance (EPR), electric polarization measurement, and theoretical calculations based on density functional theory [6].
Development of advanced diluted magnetic semiconductors with rare earth doping technology
(University of Western Australia, 2007-10-15) Photongkam, P; Ionescu, M; Zeng, R; Yu, DH; Li, S
Direct evidence of Ni magnetic moment in TbNi2Mn—X-ray magnetic circular dichroism
(Elsevier, 2014-12-01) Yu, DH; Huang, MJ; Su, HC; Lin, HJ; Chen, CT; Campbell, SJ; Wang, JL
We have investigated the individual magnetic moments of Ni, Mn and Tb atoms in the intermetallic compound TbNi2Mn in the Laves phase (magnetic phase transition temperature TC ~131 K) by X-ray magnetic circular dichroism (XMCD) studies at 300 K, 80 K and 20 K. Analyses of the experimental results reveal that Ni atoms at 20 K in an applied magnetic field of 1 T carry an intrinsic magnetic moment of spin and orbital magnetic moment contributions 0.53±0.01 μB and 0.05±0.01 μB, respectively. These moment values are similar to those of the maximum saturated moment of Ni element. A very small magnetic moment of order <0.1 μB has been measured for Mn. This suggests that Mn is antiferromagnetically ordered across the two nearly equally occupied sites of 16d and 8a. A magnetic moment of up to ~0.3 μB has been observed for the Tb atoms. Identification of a magnetic moment on the Ni atoms has provided further evidence for the mechanism of enhancement of the magnetic phase transition temperature in TbNi2Mn compared with TbNi2 (TC~37.5 K) and TbMn2 (TC~54 K) due to rare earth–transition metal (R–T) and transition metal–transition metal (T–T) interactions. The behaviour of the X-ray magnetic circular dichroism spectra of TbNi2Mn at 300 K, 80 K and 20 K – above and below the magnetic ordering temperature TC ~131 K – is discussed. © 2014 Elsevier
Disorder-induced spin-liquid-like behavior in kagome-lattice compounds
(American Physical Society (APS), 2020-12-15) Ma, Z; Dong, ZY; Wu, S; Zhu, Y; Bao, S; Cai, Z; Wang, W; Shangguan, Y; Wang, J; Ran, K; Yu, DH; Deng, GC; Mole, RA; Li, HF; Yu, SL; Li, JX; Wen, JS
Quantum spin liquids (QSLs) are an exotic state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. Here, by performing comparative experimental studies on two kagomé-lattice QSL candidates, Tm3Sb3Zn2O14 and Tm3Sb3Mg2O14, which are isostructural to each other but with strong and weak structural disorder, respectively, we show unambiguously that the disorder can induce spin-liquid-like features. In particular, both compounds show dominant antiferromagnetic interactions with a Curie-Weiss temperature of -17.4 and -28.7 K for Tm3Sb3Zn2O14 and Tm3Sb3Mg2O14, respectively, but remain disordered down to about 0.05 K. Specific-heat results suggest the presence of gapless magnetic excitations characterized by a residual linear term. Magnetic excitation spectra obtained by inelastic neutron scattering (INS) at low temperatures display broad continua. All these observations are consistent with those of a QSL. However, we find in Tm3Sb3Zn2O14, which has strong disorder resulting from the random mixing of the magnetic Tm3+ and nonmagnetic Zn2+, that the low-energy magnetic excitations observed in the specific-heat and INS measurements are substantially enhanced compared to those of Tm3Sb3Mg2O14, which has much less disorder. We believe that the effective spins of the Tm3+ ions in the Zn2+/Mg2+ sites give rise to the low-energy magnetic excitations, and the amount of the occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder. ©2020 American Physical Society.
Does the boson peak survive in an ultrathin oxide glass?
(arXiv.org, 2019-07-29) Cortie, DL; Cyster, MJ; Smith, JS; Iles, GN; Wang, XL; Mitchell, DRG; Mole, RA; de Souza, NR; Yu, DH; Cole, JH
Bulk glasses exhibit extra vibrational modes at low energies, known as the boson peak. The microscopic dynamics in nanoscale alumina impact the performance of qubits and other superconducting devices, however the existence of the boson peak in these glasses has not been previously measured. Here we report neutron spectroscopy on Al/Al2O3−x nanoparticles consisting of spherical metallic cores from 20 to 1000 nm surrounded by a 3.5 nm thick alumina glass. An intense low-energy peak is observed at ωBP = 2.8 ± 0.6 meV for highly oxidised particles, concurrent with an excess in the density of states. The intensity of the peak scales inversely with particle size and oxide fraction indicating a surface origin, and is red-shifted by 3 meV with respect to the van-Hove singularity of γ-phase Al2O3−x nanocrystals. Molecular dynamics simulations of α-Al2O3−x, γ-Al2O3−x and a-Al2O3−x show that the observed boson peak is a signature of the ultrathin glass surface, and the frequency is softened compared to that of the hypothetical bulk glass.
Dominant Kitaev interactions in the honeycomb materials Na3Co2SbO6 and Na2Co2TeO6
(American Physical Society (APS), 2022-07-01) Sanders, AL; Mole, RA; Liu, J; Brown, AJ; Yu, DH; Ling, CD; Rachel, S
Cobaltates with 3d based layered honeycomb structure were recently proposed as Kitaev magnets and putative candidates to host the long-sought Kitaev spin liquid. Here we present inelastic neutron scattering results down to 50 mK for powder samples of Na3Co2SbO6 and Na2Co2TeO6, with high resolution in regions of low momentum and energy transfers. We compare the experimental data below the antiferromagnetic zigzag ordering temperature with dynamical structure factors obtained within spin wave theory. We search the wide parameter range of a K-J1-Γ-Γ′-J3 spin 1/2 model and identify the best fits to constant momentum cuts of the inelastic neutron data. The powder average limits our ability to uniquely select a best-fit model, but we find that the experimental data is matched equally well by two classes of parameters: one with a dominant K<0, |K/J1|∼5...25, and another with K>0, |K/J1|∼1. We show that these classes are equivalent under the exact self-duality transformation identified by Chaloupka and Khalliulin [Phys. Rev. B 92, 024413 (2015)10.1103/PhysRevB.92.024413]. This model symmetry unifies a number of previous parameter estimates. Though the two cases are indistinguishable by our experiment, there is evidence in favor of the K<0 case. A purely isotropic Heisenberg model is incompatible with our results. ©2024 American Physical Society. All rights reserved.

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