Browsing by Author "Deng, GC"
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- ItemCoexistence of long-range magnetic ordering and singlet ground state in the spin-ladder superconductor SrCa13Cu24O41(American Physical Society, 2013-11-26) Deng, GC; Kenzelmann, M; Danilkin, SA; Studer, AJ; Pomjakushin, V; Imperia, P; Pomjakushina, E; Conder, KA long-range magnetic order was discovered in the quasi-one-dimensional spin-ladder compound SrCa13Cu24O41 by susceptibility, specific heat, and neutron diffraction experiments. The temperature dependence of the magnetic Bragg peak intensity could be well fitted to the power law with a transition temperature TN = 4.23 K and a critical exponent β = 0.28, indicating a three-dimensional phase transition for a low-dimensional magnet. A computer program was coded and found two possible magnetic structure models fitting best with all the observed magnetic peaks. These models suggest the spin-ladder sublattice is magnetically ordered with Cu moments aligning along the a axis. The spin interactions are primarily antiferromagnetic along rungs and legs, while there are ferromagnetic clusters along legs. Surprisingly, the singlet-triplet spin-gap excitation is observable above and below TN, indicating a coexistence of the spin-singlet ground state and long-range magnetic ordering state in this compound. © 2013 American Physical Society.
- ItemDisorder-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, JSQuantum 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.
- ItemDynamical mechanism of phase transitions in a-site ferroelectric relaxor (Na1/2Bi1/2)TiO3(Australian Institute of Physics, 2016-02-02) Deng, GC; Danilkin, SA; Imperia, P; Li, X; Zhao, XB; Luo, HQ
- ItemDynamical mechanism of phase transitions in a-site ferroelectric relaxor (Na1/2Bi1/2)TiO3(APS Physics, 2014-10-13) Deng, GC; Danilkin, SA; Zhang, HW; Imperia, P; Li, XB; Zhao, X; Luo, HQThe dynamical phase transition mechanism of (Na1/2Bi1/2)TiO3 (NBT) was studied using inelastic neutron scattering. Softening was observed of multiple phonon modes in the phase transition sequence of NBT. As usual, the softening of the zone center transverse optical modes Δ5 and Σ3 was observed in the (200) and (220) zones, showing the Ti vibration instabilities in TiO6 octahedra for both cubic-tetragonal (C-T) and tetragonal-rhombohedral (T-R) phase transitions. In these two phase transitions, however, Ti4+ has different preferential displacement directions. Surprisingly, the longitudinal optic mode also softens significantly toward the zone center in the range of the transition temperature, indicating the Na+/Bi3+ vibration instability against TiO6 octahedra during the T-R phase transition. Strong inelastic diffuse scattering shows up near M(1.5, 0.5, 0) and R(1.5, 1.5, 0.5) in the tetragonal and rhombohedral phases, respectively, indicating the condensations of the M3 and R25 optic modes for the corresponding transitions. This reveals the different rotation instabilities of TiO6 in the corresponding transition temperature range. Bottleneck or waterfall features were observed in the dispersion curves at certain temperatures but did not show close correlations to the formation of polar nanoregions. Additional instabilities could be the origin of the complexity of phase transitions and crystallographic structures in NBT. © 2014 American Physical Society.
- ItemDynamical mechanism of phase transitions in a-site ferroelectric relaxor (Na1/2Bi1/2)TiO3(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Deng, GC; Danilkin, SA; Zhang, HW; Imperia, P; Li, XB; Zhao, X; Luo, HQThe dynamical phase transition mechanism of (Na1/2Bi1/2)TiO3 (NBT) was studied using inelastic neutron scattering. Softening of multiple phonon modes were observed to correlate with the phase transition sequence of NBT. As usual, the softening of the zone centre transverse optic (TO) modes Δ5 and Σ3 was observed in (200) and (220) zone, showing the Ti vibration instabilities in TiO6 octahera for both cubic-tetragonal (C-T) and tetragonal rhombohedral (T-R) phase transitions. In this two phase transitions, however, Ti4+ has different preferential displacement directions. Surprisingly, the longitudinal optic (LO) mode also soften significantly toward zone centre in the vicinity range of the transition temperature, indicating the Na+/Bi3+ vibration instability against TiO6 octahera during the R-T phase transition. Strong inelastic diffuse scattering shows up near M(1.5, 0.5, 0) and R(1.5, 1.5, 0.5) in the tetragonal and rhombohedral phases, respectively, indicating the condensations of the M3 and R25 optic modes for the corresponding phase transitions. This reveals the rotation instabilities of TiO6 in the corresponding phase transition temperature range. Bottleneck or waterfall features were observed in the dispersion curves at certain temperatures, but did not show the close correlations to the formation of polar nanoregions (PNRs). Additional instabilities are the origin of the complexity of phase transitions and crystallographic structures in NBT.
- ItemElectron doping effects on the spin spectroscopy of BaFe2-xNixAs2 superconductors(International Conference on Neutron Scattering, 2017-07-12) Luo, HQ; Gong, DL; Xie, T; Lu, XY; Kamazawa, K; Iida, K; Kajimoto, R; Ivanov, AS; Adroja, DT; Kulda, J; Danilkin, SA; Deng, GC; Li, SL; Dai, PCHigh-temperature superconductivity in iron pnictides emerges from electron or hole doped parent compounds with antiferromagnetic order, which is argued to be associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. With more than 6 years\' efforts, we have used time-of-flight neutron spectroscopy to extensively map out the spin excitations in the electron-doped BaFe2-xNixAs2 especially around the overdoped zone boundary of superconductivity. We have found that the high energy spin fluctuations survive in the extremely high doping x=0.6 far beyond the superconducting dome, but the low energy spin excitations including the spin resonance mode is very sensitive to the electron dopings, by finally forming a large spin gap just after the disappearance of superconductivity in the overdoped regime. Further polarized neutron analysis indicate that the spin gap actually is anisotropic, and the longitudinal mode of spin fluctuations, as a hallmark of the itinerant magnetism from Fermi surface nesting, is totally eliminated together with the hole pockets near the electron-overdoped zone boundary of superconductivity.Our results suggest that the strong fluctuations from local moments give framework for magnetic interaction, while itinerant spin excitations originated from Fermi surface nesting are crucial to the superconductivity in iron pnictides.
- ItemElectron doping evolution of the magnetic excitations in BaFe(2-x)NixAs2(American Physical Society., 2013-10-25) Luo, HQ; Lu, XY; Zhang, R; Wang, M; Goremychkin, EA; Adroja, DT; Danilkin, SA; Deng, GC; Yamani, Z; Dai, PCWe use inelastic neutron scattering (INS) spectroscopy to study the magnetic excitations spectra throughout the Brillouin zone in electron-doped iron pnictide superconductors BaFe2-xNixAs2 with x = 0.096,0.15,0.18. While the x = 0.096 sample is near optimal superconductivity with T-c = 20 K and has coexisting static incommensurate magnetic order, the x = 0.15,0.18 samples are electron overdoped with reduced T-c of 14 and 8 K, respectively, and have no static antiferromagnetic (AF) order. In previous INS work on undoped (x = 0) and electron optimally doped (x = 0.1) samples, the effect of electron doping was found to modify spin waves in the parent compound BaFe2As2 below similar to 100 meV and induce a neutron spin resonance at the commensurate AF ordering wave vector that couples with superconductivity. While the new data collected on the x = 0.096 sample confirm the overall features of the earlier work, our careful temperature dependent study of the resonance reveals that the resonance suddenly changes its Q width below T-c similar to that of the optimally hole-doped iron pnictides Ba0.67K0.33Fe2As2. In addition, we establish the dispersion of the resonance and find it to change from commensurate to transversely incommensurate with increasing energy. Upon further electron doping to overdoped iron pnictides with x = 0.15 and 0.18, the resonance becomes weaker and transversely incommensurate at all energies, while spin excitations above similar to 100 meV are still not much affected. Our absolute spin excitation intensity measurements throughout the Brillouin zone for x = 0.096,0.15,0.18 confirm the notion that the low-energy spin excitation coupling with itinerant electron is important for superconductivity in these materials, even though the high-energy spin excitations are weakly doping dependent. © 2013, American Physical Society.
- ItemGiant magnetic in-plane anisotropy and competing instabilities in Na3Co2SbO6(American Physical Society, 2022-12-02) Li, XT; Gu, YC; Chen, Y; Garlea, VO; Iida, K; Kamazawa, K; Li, YM; Deng, GC; Xiao, Q; Zheng, XQ; Ye, Z; Peng, YY; Zaliznyak, IA; Tranquada, JM; Li, YWe report magnetometry data obtained on twin-free single crystals of Na3Co2SbO6, which is considered a candidate material for realizing the Kitaev honeycomb model for quantum spin liquids. Contrary to a common belief that such materials can be modeled with the symmetries of an ideal honeycomb lattice, our data reveal a pronounced twofold symmetry and in-plane anisotropy of over 200%, despite the honeycomb layer’s tiny orthorhombic distortion of less than 0.2%. We further use magnetic neutron diffraction to elucidate a rich variety of field-induced phases observed in the magnetometry. These phases manifest themselves in the paramagnetic state as diffuse scattering signals associated with competing ferromagnetic and antiferromagnetic instabilities, consistent with a theory that also predicts a quantum spin liquid phase nearby. Our results call for theoretical understanding of the observed in-plane anisotropy and render Na3Co2SbO6 a promising ground for finding exotic quantum phases by targeted external tuning. © Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
- ItemGiant shifts of crystal-field excitations in ErFeO3 driven by internal magnetic fields(Cornell University, 2021-09-16) O'Brien, J; Deng, GC; Ma, XX; Feng, ZJ; Ren, W; Cao, SX; Yu, DH; McIntyre, GJ; Ulrich, CCrystal-field excitations in transition-metal oxides where -rare-earth elements locate in the space between the transition-metal-oxide tetrahedra and octahedra, are assumed to be robust with respect to external perturbations such as temperature. Using inelastic neutron-scattering experiments, a giant shift of the energy of the lowest crystal-field excitation of Er3+ (4I15/2) in ErFeO3 from 0.35 meV to 0.75 meV was observed on cooling from 10K to 1.5K through the magnetic ordering temperature of Er3+ at 4.1 K. A crystal-field model was proposed to explain the observed crystal field excitations in this work. The model indicates the lowest-energy crystal-field excitation in ErFeO3 is the first Kramers doublet above the ground state. Its energy substantially shifts by the internal field induced by the ordered Er3+ magnetic moments. Further magnetic-field-dependent measurements provide strong supportive evidence for this scenario. By fitting the external magnetic-field dependency of the crystal-field excitation energy, the internal field generated by Er3+ magnetic moments was derived to be ~0.33meV. The result indicates that the internal field of Er3+ magnetic moments contribute to the energy shift of the crystal-field excitations. The giant energy shift under fields could be attributed to the anisotropy of the large effective g-factor. CC BY: Creative Commons Attribution
- ItemLarge easy-plane anisotropy induced spin reorientation in magnetoelectric materials (Co4−xMnx)Nb2O9(IOP Science, 2019-03-29) Deng, GC; Yu, YS; Cao, YM; Feng, ZJ; Ren, W; Cao, SX; Studer, AJ; Hester, JR; Kareri, Y; Ulrich, C; McIntyre, GJNeutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co4−xMnx)Nb2O9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Neel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co4Nb2O9, the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn4Nb2O9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn4Nb2O9 into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co2+ and relative small Ising-like anisotropy of Mn2+. The doping effects on the Néel temperature and occupancy are also discussed. © 2019 IOP Publishing Ltd
- ItemMagnetic structure and spin dynamics of multiferroic system Co4Nb2O9(Australian Institute of Physics, 2017-02-01) Deng, GC; Cao, YM; Ren, W; Cao, SX; Gauthier, N; Kenzelmann, M; Studer, AJ; Rule, KC; Gardner, JS; Davison, G; Imperia, P; McIntyre, GJCo4Nb2O9, was recently reported to have large magneto-dielectric coupling effect under a certain magnetic field. This compound has a corundum-type crystal structure of space group P-3c1 of ref. and undergoes antiferromagnetic phase transition around 27 K. It was previously believed that the magnetic moments of Co2+ order into a collinear antiferromagnetic structure in which Co2+ spins order parallel to the c-direction and form ferromagnetic chains with antiparallel inter-chain coupling. However, the recent study has shown that this magnetic structure model is incorrect. In this study, we found that the Co2+ magnetic moments align in the ab plane with a non-collinear configuration. Using inelastic neutron scattering, we measured the spin wave excitation from its magnetic phase along (h00) and (00l). A magnetic model was proposed to explain the observed spin dynamical behavior. There are two inequivalent Co sites, which form spin chains in an alternative way along c axis. Each Co2+ moment couples with its two inequivalent neighbors on the same chain with ferromagnetic interactions. Co2+ moments from each site form a zig-zag hexagonal ring perpendicular to the c axis, where antiferromagnetic interactions dominate. On the basis of this model, the observed spin wave spectra can be well simulated by SpinW.
- ItemThe magnetic structures and transitions of a potential multiferroic orthoferrite ErFeO3(AIP Publishing, 2015-04-29) Deng, GC; Guo, P; Ren, W; Cao, SX; Maynard-Casely, HE; Avdeev, M; McIntyre, GJRare-earth orthoferrites are very interesting due to their appealing optical and multiferroic properties. In this study, the magnetic structures and transitions of a typical rare-earth orthoferrite, ErFeO3, have been reinvestigated in detail. The spin-reorientation transition of the Fe3+ magnetic phase and the low-temperature magnetic ordering of Er3+ were observed by neutron powder diffraction. The corresponding magnetic structures have been solved anew by symmetry analysis and refinement of the diffraction results. The magnetic moments of Fe3+ align in an antiferromagnetic way along the c axis with a weak ferromagnetic component along the b axis below the Néel temperature and above the spin-reorientation transition. Below the spin-reorientation transition, the Fe3+ moments rotate into an antiferromagnetic ordering state along the b axis with weak ferromagnetic alignment along the c axis. The spin-reorientation takes place in the bc plane. The Er3+ moments align antiferromagnetically with a Cy mode below 4.5 K. For the Fe3+ moments, an additional Cx mode is induced by the ordering of the Er3+ moments. Namely, they change from GyFz mode into CxGyFz mode in the Pnma space-group setting. This study resolves the long-lasting dispute about the magnetic structure of ErFeO3 at low temperature. © 2015 AIP Publishing LLC.
- ItemNeutron diffuse scattering of (1 − x)(Na0.5Bi0.5)TiO3–xBaTiO3 relaxor ferroelectric single crystals(Elsevier, 2014-09-01) Zhang, HW; Deng, GC; Studer, AJ; Li, XB; Zhao, X; Luo, HQPeculiar L-shaped diffuse streaks along <0 0 1>pc were observed in (Na0.5Bi0.5)TiO3 (NBT) below the Burns temperature, revealing the existence of polar nanoregions (PNRs). The displacement of Bi3+ cations is ∼0.26 Å along <0 0 1>pc in the PNRs, with a size of ∼13 Å in NBT. The BaTiO3 doping drives the diffuse scattering patterns to evolve from the L-shape into an ellipsoidal along <0 1 1 >pc in (Na0.5Bi0.5)TiO3–xBaTiO3. An abnormally large correlation length was observed in the morphotropic phase boundary composition with x = 0.05. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.
- ItemOrigin of magnetoelectric coupling effect and spin dynamics of multiferroic system Co4Nb2O9(International Conference on Neutron Scattering, 2017-07-12) Deng, GC; Cao, YM; Ren, W; Cao, SX; Studer, AJ; Gauthier, N; Kenzelmann, M; Davison, G; Rule, KC; Gardner, JS; Imperia, P; Ulrich, C; McIntyre, GJCo4Nb2O9,was recently reported to have large magnetoelectric coupling effect under a certain magnetic field. This compound has a crystal structure (space group P-3c1) derived from corundum structure and undergoes antiferromagnetic phase transition around 27K. It was previously believed that the magnetic moments of Co2+ order into a collinear antiferromagnetic structure in which magnetic moments are parallel to the c axis and form ferromagnetic chains with antiparallel inter-chain coupling. However, the recent study has shown that this magnetic structure model is incorrect. In this study, we found that the Co2+magnetic moments on both Co1 and Co2 sites align in the ab plane with a non-collinear configuration. Using inelastic neutron scattering, we measured the spin wave excitation from its magnetic phase along (h00) and (00l). A spin dynamic model proposed in this study is able to explain the observed spin dynamical behavior quite well. The nearest and next nearest neighbor interactions (NN and NNN) along the c axis are ferromagnetic. The interaction on the zig-zag ring of Co1 perpendicular to the c axis is highly frustrated while that of the zig-zag ring of Co2 is antiferromagnetic. The single ion anisotropy and Dzyaloshinskii-Moriya (DM) interaction contribute to the spin dynamics of Co4Nb2O9 as well. The simulated spin wave excitation by using SpinW[5] matches the experimental data very well. The DM interaction, which is most probably due to the triangle Co2-O-Co2 bond, was found to be the origin of the magnetoelectric coupling in this compound.
- ItemSIKA - the cold-neutron triple-axis spectrometer with multiplexing analyzer at Bragg Institute(Asia - Oceania Neutron Scattering Association, 2015-07-19) Deng, GC; McIntyre, GJ; Wu, CM; Gardner, JS; Vorderwisch, P; Li, WHSIKA is a high-flux cold-neutron triple-axis spectrometer funded by Ministry of Science and Technology of Taiwan and currently being operated by National Synchrotron Radiation Research Center. It locates at the OPAL reactor face at the Australian Nuclear Science and Technology Organisation (ANSTO). Its incident energy ranges from 2.5meV to 30meV with the highest flux at ~8meV. With an advanced design, SIKA is equipped with an analyzer array of 13 PG(002) blades (Fig. 1), a multi-wire detector, and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or in various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. Several typical mapping modes are analyzed and simulated using Monte Carlo ray-tracing package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. In hotcommissioning, a multiplexing mode with constant Ef was used to measure the phonon dispersion in a Pb single crystal. The simulation and experiment results demonstrate the flexibility and fast data-collecting potential of SIKA as a next generation cold neutron triple-axis spectrometer.
- ItemSimulation and implementation of multiplexing modes on cold-neutron triple-axis spectrometer SIKA(Elsevier, 2020-04-11) Deng, GC; McIntyre, GJSIKA, a high-flux cold-neutron triple-axis spectrometer at the open-pool Australian lightwater reactor (OPAL) at the Australian Nuclear Science and Technology Organisation (ANSTO), is equipped with a 13-blade analyser and position-sensitive detector. This multiplexing design endows SIKA high flexibility to run in both traditional triple-axis and multiplexing analyser modes. In this study, two different multiplexing modes on SIKA are simulated using Monte Carlo ray-tracing methods. The simulation results demonstrate SIKA’s capabilities to work in these operational modes, especially, the multi-Q const-Ef mode, where Q is the scattering wavevector and Ef is the final neutron energy. This capability was demonstrated by measuring the phonon dispersion of a Pb single-crystal sample with the multi-Q const-Ef mode on SIKA. Compared to the traditional and multi-analyser triple-axis spectrometers, multiplexing modes on SIKA combine the advantages of the high data-acquisition efficiency and flexibility to focus on local areas of interest in the momentum-energy transfer space, namely, the (Q, ħ ω) space. Crown Copyright © 2020 Published by Elsevier B.V.
- ItemSimulation of energy dispersive mode for RITA-type cold neutron triple axis spectrometer SIKA(Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WHSIKA, a high flux cold triple axis spectrometer at OPAL reactor, is equipped with a 13-blade analyser and position sensitive detector. This multiplexing design endows SIKA with high flexibility to run in either traditional or dispersive modes. In this study, the energy dispersive mode for two different energy transfers is simulated using the Monte Carlo ray-trace package SIMRES. The results show that SIKA could work effectively in this mode at low and intermediate energy transfers with reasonable energy and Q resolution. The simulated energy resolution is about 0.23 meV for an energy transfer of ħω = 5 meV and increases to 1.8 meV for ħω = 15 meV. This work provides a valuable reference for future inelastic neutron scattering experiments on SIKA.
- ItemSimulation of multiple operation modes for the cold neutron triple axis spectrometer SIKA at Bragg Institute(Australian Institute of Physics, 2012-02-02) Deng, GC; Vorderwisch, P; Wu, CM; McIntyre, GJ; Li, WHThe coming high flux cold-neutron triple axis spectrometer, SIKA at Bragg Institute, is built with an unconventional design, equipped with a multi-strip analyzer array of 13 PG(002) blades (see Fig. 1), a linear position-sensitive detector and a separate diffraction detector. Such a design allows SIKA to run in a traditional step-by-step mode or various mapping (or dispersive) modes by changing the configuration of analyzers and detectors. In this study, several typical mapping modes are analyzed and simulated using Monte Carlo ray-trace package SIMRES of RESTRAX. [1] The performance of different mapping modes are demonstrated and evaluated, providing the dispersion relations of these operation modes as references for experimental studies. The simulation shows the flexibility and fast data collecting potential of SIKA as a new generation of triple axis spectrometer. The simulated data could be compared with the experimental data in the future and as a reference to the selection of effective operation modes.
- ItemSpin dynamics and magnetoelectric coupling mechanism of Co4Nb2O9(American Physical Society, 2018-02-28) Deng, GC; Cao, YM; Ren, W; Cao, SX; Studer, AJ; Gauthier, N; Kenzelmann, M; Davidson, G; Rule, KC; Gardner, JS; Imperia, P; Ulrich, C; McIntyre, GJNeutron powder diffraction experiments reveal that Co4Nb2O9 forms a noncollinear in-plane magnetic structure with Co2+ moments lying in the ab plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest- and next-nearest-neighbor exchange interactions, in-plane anisotropy, and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of Co4Nb2O9 is attributed to the large in-plane anisotropy, while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of Co4Nb2O9 in fields can be explained by its special in-plane magnetic structure. ©2018 American Physical Society
- ItemSpin dynamics of edge-sharing spin chains in SrCa13Cu24O41(American Physical Society, 2018-11-12) Deng, GC; Yu, DH; Mole, RA; Pomjakushina, E; Conder, K; Kenzelmann, M; Yano, SI; Wang, CW; Rule, KC; Gardner, JS; Luo, HQ; Li, S; Ulrich, C; Imperia, P; Ren, W; Cao, SX; McIntyre, GJThe low-energy magnetic excitation from the highly Ca-doped quasi-one-dimensional magnet SrCa13Cu24O41 was studied in the magnetic ordered state by using inelastic neutron scattering. We observed the gapless spin-wave excitation, dispersive along the a and c axes but nondispersive along the b axis. Such excitations are attributed to the spin wave from the spin-chain sublattice. Model fitting to the experimental data gives the nearest-neighbor interaction Jc as 5.4 meV and the interchain interaction Ja=4.4meV. Jc is antiferromagnetic and its value is close to the nearest-neighbor interactions of the similar edge-sharing spin-chain systems such as CuGeO3. Comparing with the hole-doped spin chains in Sr14Cu24O41, which shows a spin gap due to spin dimers formed around Zhang-Rice singlets, the chains in SrCa13Cu24 O41 show a gapless excitation in this paper. We ascribe such a change from gapped to gapless excitations to holes transferring away from the chain sublattice into the ladder sublattice upon Ca doping. ©2018 American Physical Society