Browsing by Author "Wang, CW"

Now showing 1 - 20 of 25
  • No Thumbnail Available
    Item
    Antiferromagnetic spin structure and negative thermal expansion of Li2Ni(WO4)2
    (American Physical Society, 2015-07-10) Karna, SK; Wang, CW; Sankar, R; Avdeev, M; Singh, A; Panneer Muthuselvam, I; Singh, VN; Guo, GY; Chou, FC
    We report the results of a study on the crystal and magnetic structure of Li2Ni(WO4)2 with a neutron diffraction technique. The Ni2+ spins of S = 1 for NiO6 octahedra are coupled via corner-sharing, nonmagnetic double tungstate groups in a super-superexchange route. Two magnetic anomalies at TN1∼ 18 K and TN2∼ 13 K are revealed from the measured magnetic susceptibility χ(T), and TN2 is confirmed to be the onset of a commensurate long-range antiferromagnetic (AF) ordering through neutron diffraction. A negative thermal expansion phenomenon is observed below TN2, which has been interpreted as a result of competing normal thermal contraction and long-range AF spin ordering through counterbalanced WO4 and NiO6 polyhedral local distortion. The AF spin structure has been modeled and used to show that Ni spins with a saturated magnetic moment of ∼1.90(27)μB that lies in the a−c plane approximately 46∘(±10∘) off the a axis. The experimental results are compared and found to be consistent with theoretical calculations using density-functional theory with a generalized gradient approximation plus on-site Coulomb interaction. ©2015 American Physical Society
  • Thumbnail Image
    Item
    Commensurate to incommensurate magnetic phase transition in the type-II multiferroic YBaCuFeO5
    (Australian Institute of Physics, 2015-02-06) Lai, YC; Chen, WT; Wang, CW; Rule, KC; Chou, FC; Du, CH
    The simultaneous existence of magnetic and ferroelectric ordering is a characteristic of multiferroic materials. The search for new multiferroics is partly motivated by the need for non-volatile random access memories for which the electric polarisation (magnetisation) is controlled by magnetic field (electric field) or vice versa. The use of such materials would be extremely beneficial for the next generation of electronic devices (mobile phones, tablets etc) whereby compact size constraints are important as well as optimising reading/writing speeds and power consumption. YBaCuFeO5 has been classified as a type-II multiferroic due to its complex magnetic interactions and low temperature feroelectricity. Two magnetic phase transitions of antiferromagnetic nature have been found near TN1 = 450 K and TN2 = 170 K. The first represents the ordering of the Fe3+ ions into a commensurate antiferromagnetic state, while the second represents the ordering of the Cu2+ ions giving an overall incommensurate antiferromagnetic ground state. For the first time, using modified traveling solvent floating zone growth method, we have been able to grow a centimeter-sized, high-quality, singlecrystal of YBaCuFeO5. Magnetisation and neutron diffraction results indicate a complex magnetic phase diagram in this material with a strong hysteresis effect and a chiral magnetic ground state.
  • Thumbnail Image
    Item
    Complex magnetic incommensurability in multiferroic Co3TeO6
    (International Conference on Neutron Scattering, 2017-07-12) Lee, CH; Wang, CW; Zhao, Y; Li, WH; Lynn, JW; Harris, AB; Rule, KC; Yang, HD; Berger, H
    Monoclinic cobalt tellurate Co3TeO6 has been characterized1-3 as a type-II multiferroic, where the order parameters of electrical polarization and spontaneous magnetization are closely coupled.4,5 In this study, polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below TM1= 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions in the crystal. Below TM2 = 19.5 K, additional commensurate magnetic peaks develop, consistent with the ?4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below TM3 = 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, a commensurate ?3 irreducible representation appears, and the k component of the ICM wave vector disappears. Below TM4= 15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.
  • No Thumbnail Available
    Item
    Controlling spin orientation and metamagnetic transitions in anisotropic van der Waals antiferromagnet CrPS4 by hydrostatic pressure
    (Wiley, 2022-02) Peng, Y; Lin, Z; Tian, G; Yang, J; Zhang, P; Wang, F; Gu, P; Liu, X; Wang, CW; Avdeev, M; Liu, F; Zhou, D; Han, R; Shen, P; Yang, W; Liu, S; Ye, Y; Yang, J
    Controlling the phases of matter is a central task in condensed matter physics and materials science. In 2D magnets, manipulating spin orientation is of great significance in the context of the Mermin–Wagner theorem. Herein, a systematic study of temperature‐ and pressure‐dependent magnetic properties up to 1 GPa in van der Waals CrPS4 is reported. Owing to the temperature‐dependent change of the magnetic anisotropy energy, the material undergoes a first‐order spin reorientation transition with magnetic moments realigning from being almost parallel with the c axis in the ac plane to the quasi‐1D chains of CrS6 octahedra along the b axis upon heating. The spin reorientation temperature is suppressed after applying pressure, shifting the high‐temperature phase to lower temperatures with the emergence of spin‐flop transitions under magnetic fields applied along the b axis. The saturation field increases with pressure, indicating the enhancement of interlayer antiferromagnetic coupling. However, the Néel temperature is slightly reduced, which is ascribed to the suppression of intralayer ferromagnetic coupling. The work demonstrates the control of spin orientation and metamagnetic transitions in layered antiferromagnets, which may provide new perspectives for exploring 2D magnetism and related spintronic devices. © 2021 Wiley-VCH GmbH.
  • Thumbnail Image
    Item
    Experimental observation of long-range magnetic order in icosahedral quasicrystals
    (American Chemical Society, 2021-11-17) Tamura, R; Ishikawa, A; Suzuki, S; Kotajima, T; Tanaka, Y; Seki, T; Shibata, N; Yamada, T; Fujii, T; Wang, CW; Avdeev, M; Nawa, K; Okuyama, D; Sato, TJ
    Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals (i QCs) Au–Ga–Gd and Au–Ga–Tb. The Au65Ga20Gd15i QC exhibits a ferromagnetic transition at TC = 23 K, manifested as a sharp anomaly in both magnetic susceptibility and specific heat measurements, along with an appearance of magnetic Bragg peak below TC. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviors observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e., for the Au65Ga20Tb15i QC, a ferromagnetic behavior is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15i QC becomes broadened upon Tb substitution, neutron diffraction experiments clearly show marked development of magnetic Bragg peaks just below TC, indicating long-range magnetic order for the Au65Ga20Tb15i QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with unprecedented highest global symmetry, i.e., icosahedral symmetry. © 2021 The Authors - CC BY. Published by American Chemical Society
  • No Thumbnail Available
    Item
    Large magnetoresistance and charge transfer between the conduction and magnetic electrons in layered oxyselenide BiOCu0.96Se
    (Royal Society of Chemistry, 2013-8-27) Karna, SK; Hung, CH; Wu, CM; Wang, CW; Li, WH; Sankar, R; Chou, FC; Avdeev, M
    The electrical and magnetic properties of slightly Cu-deficient BiOCu0.96Se have been investigated using neutron and X-ray diffraction, ac magnetic susceptibility, magnetization and electric resistivity measurements. The layered BiOCu0.96Se crystallizes into a tetragonal lattice with a P4/nmm symmetry. Thermal profiles of the electrical resistivity reveal a semiconductor type behavior, but depart from its course at low temperatures when antiferromagnetic coupling becomes thermally loosened at 140 K. Positive magnetoresistances are obtained at all temperatures studied. With an applied magnetic field of 0.5 kOe, the magnetoresistance reaches 235% at 2 K. It decreases with increasing temperature, but stabilizes to 70% above 60 K. Both ferromagnetic and antiferromagnetic coupling are detected between the Cu spins in the SeCu4 pyramidal blocks, which results in a non-collinear spin arrangement at low temperatures. The antiferromagnetic component becomes disordered above TN = 140 K, whereas the ferromagnetic moment persists up to TC = 300 K. Interlayer charge transfer between the conduction and magnetic electrons gives rise to an anomaly in the magnetic order parameter. © 2013, Royal Society of Chemistry.
  • Thumbnail Image
    Item
    Long-range magnetic order in real icosahedral quasicrystals
    (Research Square, 2021-03-22) Tamura, R; Ishikawa, A; Suzuki, S; Kotajima, A; Tanaka, Y; Seki, T; Shibata, N; Yamada, T; Fujii, T; Wang, CW; Avdeev, M; Sato, T
    Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals (i QCs) Au–Ga–Gd and Au–Ga–Tb. The Au65Ga20Gd15 i QC exhibits a ferromagnetic transition at TC = 23 K, manifested as a sharp anomaly in both magnetic-susceptibility and specific-heat measurements. Quick magnetic saturation to almost the full moment (7μB/Gd3+) is observed under 100 Oe at 2 K. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviours observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e. for the Au65Ga20Tb15 i QC, a ferromagnetic behaviour is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15 i QC is significantly broadened upon Tb substitution, neutron-diffraction experiments clearly show the marked development of magnetic Bragg peaks below TC, indicating long-range magnetic order for the Au65Ga20Tb15 i QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with unprecedented highest global symmetry, i.e. icosahedral symmetry. © This work is licensed under a CC BY 4.0 License.
  • No Thumbnail Available
    Item
    Magnetic ordering and spin dynamics in the S = 5/2 staggered triangular lattice antiferromagnet Ba2MnTeO6
    (American Physical Society, 2020-09-09) Li, L; Narayanan, N; Jin, SJ; Yu, J; Liu, ZJ; Sun, HL; Wang, CW; Peterson, VK; Liu, Y; Danilkin, SA; Yao, DX; Yu, DH; Wang, M
    We report studies of the magnetic properties of a staggered stacked triangular lattice Ba2MnTeO6 using magnetic susceptibility, specific heat, neutron powder diffraction, inelastic neutron scattering measurements, and first-principles density functional theory calculations. Neutron diffraction measurements reveal Ba2MnTeO6 to be antiferromagnetically ordered with a propagation vector k=(0.5,0.5,0) and Néel transition temperature of TN≈20 K. The dominant interaction derived from the Curie-Weiss fitting to the inverse DC susceptibility is antiferromagnetic. Modeling of the inelastic neutron scattering data with linear spin wave theory yielded magnetic exchange interactions for the nearest intralayer, nearest interlayer, and next-nearest interlayer J1=0.27(3), meV J2=0.27(3) meV, and J3=−0.05(1) meV, respectively, and a small value of easy-axis anisotropy of Dzz=−0.01 meV. We derive a magnetic phase diagram that reveals a collinear stripe-type antiferromagnetic order that is stabilized by the competition between J1, J2, and J3. ©2020 American Physical Society
  • No Thumbnail Available
    Item
    Magnetic properties and noncollinear spin structure of the tin-rich stannide Ho5Co6Sn18
    (American Physical Society, 2022-03-28) Wang, CW; Karna, SK; Yanco, SI; Lee, CH; Avdeev, M; Lue, CS; Kuo, CN
    We have investigated the magnetic, structural, and thermodynamic properties of Ho5Co6Sn18 through x-ray and neutron diffraction, magnetization, and specific heat measurements. Ho5Co6Sn18 displays a magnetic transition at TM=3.4K and can be described with the magnetic space group I41/ac′d′. The two holmium sublattices Ho(1) and Ho(2) exhibit different magnetic behaviors. Ferromagnetic order on the Ho(1) site develops into a net magnetization along the c axis below TM. In contrast, the ordering of the Ho(2) site is determined by geometric magnetic frustrations. The Ho(2) spins order into the noncollinear, two-in-two-out antiferromagnetic pattern on the Ho(2)4 tetrahedron. At 60 mK, the ordered moment of Ho(2) reaches 4.01(8)μB, which is about half of the Ho(1) moment. Upon the application of a magnetic field, ferromagnetic components along the c axis are induced on Ho(2), along with the in-plane antiferromagnetic components, indicating the XY-like spin anisotropy of the Ho(2) spins. A magnetic quasielastic neutron scattering signal is observed above TM and significantly weakens with the magnetic ordering. ©2022 American Physical Society.
  • No Thumbnail Available
    Item
    Magnetic properties of the quasicrystal approximant Au65Ga21Tb14
    (American Physical Society, 2023-05-31) Nawa, K; Avdeev, M; Ishikawa, A; Takakura, H; Wang, CW; Tamura, R; Okuyama, D; Satao, TJ; Murasaki, R
    The magnetic properties of the quasicrystal approximant Au65Ga21Tb14 were investigated using magnetization and neutron diffraction experiments. The temperature dependences of the magnetic susceptibility and magnetization curve indicate dominant ferromagnetic interactions, whereas a whirling antiferromagnetic order was observed in neutron diffraction experiments. In the antiferromagnetic phase, the magnetic moments are aligned almost perpendicular to a pseudofivefold symmetry axis, which corresponds to the easy-axis direction of a Tb atom. Magnetic properties similar to those of Au72Al14Tb14 in spite of the substantial difference in the Au concentration suggest the robustness of the easy-axis anisotropy against the chemical environment. ©2023 American Physical Society
  • Thumbnail Image
    Item
    Magnetic structure and magnetocaloric properties of LaMn2Ge2
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Wang, JL; Cheng, ZX; Wang, WQ; Wang, CW; Hutchison, WD; Campbell, SJ
    The extensive set of ternary intermetallic RMn2X2 compounds (R = rare earth, T = transitional metal, X = Ge or Si) have been investigated extensively in the past few decades due to their interesting range of physical properties [e.g. 1-3]. Recently, significant attention has been paid to the magnetocaloric effect (MCE) of RMn2X2 compounds for their potential application in magnetic refrigeration. Their MCE properties are important as RMn2X2 compounds enable a wide range of structural and magnetic behaviours and related transitions to be controlled via substitution of R, Mn, and X atoms on the 2a, 4d, and 4e sites respectively [e.g. 4-7]. We have carried out a detailed investigation of the LaMn2Ge2 compound using neutron diffraction and magnetic measurements, focusing on the magnetic behaviour of the Mn-sublattice. With decreasing temperature, the magnetic state changes from paramagnetism to incommensurate canted antiferromagnetism AFfs at TN~ 360 K and then gives way to incommensurate canted ferromagnetism Fmi below TC ~ 323 K. No obvious magnetoelastic coupling were detected from refinement of the variable neutron diffraction patterns (5 K - 450K) while detailed analyses of magnetic data indicate that the magnetic phase transition is second order. Under magnetic field changes of 2 T and 8 T, the maximum values of the magnetic entropy change (-DELTASM max) around TC reach 1.65 J/kg K and 4.42 J/kg K, respectively.
  • No Thumbnail Available
    Item
    Neutron diffraction study of unusual magnetic behaviors in the Ho2Fe11Al6 intermetallic compound
    (American Chemical Society, 2019-09-30) Cao, Y; Lin, K; Liu, ZN; Hu, JY; Wang, CW; Avdeev, M; Li, Q; Deng, JX; Chen, J; Zhang, HJ; Xing, XR
    Knowledge of structure–property relationships is fundamental but significant in the exploitation of magnetic materials. Here we report that the high Al substitution for Fe transformed the crystal structure from a hexagonal Ho2Fe17 compound to a rhombohedral Ho2Fe11Al6 compound. Intriguingly, the latter shows unusual evolution of magnetization around 86 and 220 K compared with the former. Integrated investigations of the detailed structure analysis and magnetic performance on the Ho2Fe11Al6 compound demonstrate that the Ho2Fe11Al6 compound possesses a stable rhombohedral structure (R3̅m) from 5 to 430 K with preferred occupation of Al atoms and ferrimagnetic structure in which the magnetic moments of Ho and Fe lie antiparallel in the basal plane below the Curie temperature. The results of the temperature dependence of moments reveal that the disparate rates of change of the moments for Ho and Fe sublattices give rise to unusual evolution of magnetization around 86 and 220 K and then turn to paramagnetic above 280 K. This work provides clear structure and magnetization information on the Ho2Fe11Al6 compound, which may be beneficial to guiding the future development of magnetic materials. © 2019 American Chemical Society
  • Thumbnail Image
    Item
    NSRRC neutron scattering group at ACNS
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Yano, SI; Wang, CW; Peng, H; Wu, CM
    The National synchrotron radiation research centre (NSRRC) in Taiwan has a group of scientists stationed at the Australian Centre for Neutron Scattering (ACNS), ANSTO, Australia. Three Instrument Scientists were hired to operate neutron scattering instruments and to serve users; Chun-Min Wu works on Small angle neutron scattering instruments, Chin-wei Wang is a Powder diffractometer scientist and Shinichiro Yano works on the cold triple axis spectrometer SIKA. In addition, one staff member is a software engineer. Under this arrangement, we have built the cold triple axis spectrometer SIKA in the OPAL reactor beam hall at ANSTO. SIKA was designed to study dynamics in magnetic materials in the energy range of meV and below with high resolution. The Taiwan investment adds particular value to the area of materials science whereby Taiwan and Australia both benefit. Following 10 years of construc tion, SIKA has been in the user program since 2015 July with the number of scientific publications growing steadily since then. Taiwanese users now occupy about 20 percent of international proposals submitted to ACNS in the 2018-2 proposal round whilst the Taiwanese neutron scattering community is also growing. We hope for continued good relations between NSRRC and ANSTO with a view to expanding our col laboration. We are currently in the process of hiring an additional instrument scientist who would be working on a reflectometer at ACNS. In this talk, we will present scientific outcomes from the NSRRC neutron group and updates from SIKA. © The Authors.
  • No Thumbnail Available
    Item
    Polymorphism and temperature-induced phase transitions of Na2CoP2O7
    (American Chemical Society, 2019-12-04) Avdeev, M; Wang, CW; Barpanda, P; Fujii, K; Yashima, M
    Polymorphism and temperature-induced phase transitions of Na2CoP2O7 were studied by in situ neutron powder diffraction and complemented by ab initio calculations to reconcile previous reports of its three polymorphs. We show that the “blue” form prepared at 873 K exists at room temperature in the orthorhombic Pna21 (= P21cn) phase, which transforms via a first-order transition to the tetragonal form at the temperature close to room temperature (∼335 K). Just above the transition, the tetragonal form is likely incommensurately modulated with the modulation vanishing at ∼423 K. Above that temperature the phase remains in the unmodulated tetragonal state (P42/mnm) until melting at ∼900 K. Upon cooling after melting, Na2CoP2O7 crystallizes into the “rose” triclinic P1 form which persists while it cools to room temperature, apparently stabilized by the barrier of the reconstructive “rose”–“blue” transition. We also discuss the relationship between the tetragonal and orthorhombic structures, the driving forces of the orthorhombic distortion, and similarity to Na2ZnP2O7 and the melilite-type structural family. © 2019 American Chemical Society
  • Thumbnail Image
    Item
    Powder diffraction at the Australian Centre for Neutron Scattering: recent results and capabilities
    (International Conference on Neutron Scattering, 2017-07-12) Peterson, VK; Studer, AJ; Maynard-Casely, HE; Hester, JR; Avdeev, M; Wang, CW
    Powder diffraction is a core neutron scattering tool with a long history in Australia. The Australian Centre for Neutron Scattering at the OPAL reactor facility hosts two world-class constant-wavelength neutron powder diffractometers, which share the largest beam guide in any research reactor. ECHIDNA (high resolution) is optimised for complex atomic and magnetic structure determination. Data collection proceeds in a traditional step-scan type acquisition using 128 linear position sensitive detectors with a typical scan time of 1-6 h. WOMBAT (high intensity) is one of the fastest neutron powder instruments in the world, featuring a 120 ° area detector with position sensitive detection. WOMBAT routinely measures to 1 min and down to 20 ms time resolution, with 20 μs stroboscopic measurement. Experiments often use both instruments, with detailed structure examined at discrete parameter space points on ECHIDNA and over a greater range on WOMBAT. Research examples showcasing the instruments’ capabilities will be presented. For WOMBAT, these will include the non-equilibrium real time electric field response of piezoelectric materials up to 10 kHz with multiple time bins (with the University of New South Wales) and the determination of lithium location within lithium-ion battery electrodes during battery charge-discharge cycling (with researchers at the University of Wollongong). Example equilibrium studies on ECHIDNA will include porous materials loaded with gas (with the Universities of Sydney and Melbourne, also on WOMBAT), amongst others.
  • No Thumbnail Available
    Item
    Pressure-modulated magnetism and negative thermal expansion in the Ho2Fe17 intermetallic compound
    (American Chemical Society, 2023-05-25) Cao, YL; Zhou, H; Khmelevskyi, S; Lin, K; Avdeev, M; Wang, CW; Wang, B; Hu, F; Kato,; Hattori, T; Abe, J; Ohara, K; Kawaguchi, S; Li, Q; Fukuda, M; Nishikubo, T; Lee, K; Koike, T; Liu, Q; Miao, J; Deng, JX; Shen, B; Azuma, M; Xing, X
    Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in Ho2Fe17 on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level (EF), which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials. © 2024 American Chemical Society
  • Thumbnail Image
    Item
    Quantified zero thermal expansion in magnetic R2Fe17-based intermetallic compounds (R = rare earth)
    (American Chemical Society, 2023-06-13) Cao, YL; Matsukawa, T; Gibbs, A; Avdeev, M; Wang, CW; Wu, H; Huang, QZ; Ohoyama, K; Ishigaki, T; Zhou, H; Li, Q; Miao, J; Lin, K; Xing, XR
    Zero thermal expansion (ZTE) has been a fascinating task for the past few decades due to its great scientific and practical merits. To realize ZTE, negative thermal expansion is typically employed by chemical substitutions on tuning structure features, which often relies on trial and error. Here, we report on exploring quantification of thermal expansion with magnetic ordering in an intermetallic class of R2Fe17 (R = rare earth), which can accurately determine the ZTE composition using a documented database. It demonstrates that the magnetic ordering of the Fe-sublattice contributes to the thermal expansion anomaly through simultaneous examinations of magnetization and neutron powder diffraction. Alternative elements can be manipulated on a Fe-sublattice to control both the total ordered magnetic moments of the Fe-sublattice and Curie temperature, which tailors the temperature variation of the magnetic contributions on thermal expansion. The current work might point to a future for ZTE high throughput searches, anticipated to benefit applications. © 2023 American Chemical Society
  • No Thumbnail Available
    Item
    Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice
    (American Physical Society, 2017-03-08) Karna, SK; Zhao, Y; Sankar, R; Avdeev, M; Tseng, PC; Wang, CW; Shu, GJ; Matan, K; Guo, GY; Chou, FC
    The nature of Na ion distribution, diffusion path, and the spin structure of P2-type Na2Ni2TeO6 with a Ni honeycomb lattice has been explored. The nuclear density distribution of Na ions reveals a two-dimensional (2D) chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron-diffraction technique. The Na diffusion pathway described by the calculated isosurface of the Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni2+ spin ordering were examined in detail with the neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity, and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single-crystal sample through the k scan in the momentum space corresponding to the AFM peak of (12,0,1). © 2017 American Physical Society
  • No Thumbnail Available
    Item
    Spin 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, GJ
    The 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
  • Thumbnail Image
    Item
    Spin dynamics of quasi-one-dimensional spin-ladder system SrCa13Cu24O41 in the long-range magnetic ordering state
    (Australian Institute of Physics, 2018-01-31) Deng, GC; Yu, DH; Mole, RA; Yano, SI; Wang, CW; Rule, KC; Gardner, JS; Luo, H; Li, S; Ulrich, C; Imperia, P; Ren, W; Cao, SX; Pomjakushina, E; Conder, K; Kenzelmann, M; McIntyre, GJ
    Sr14-xCaxCu24O41 is a quasi-one-dimensional magnet, which consists of two sublattices: spin ladder and spin chain, forming an incommensurate crystal structure along the c axis, namely, the ladder leg or chain direction. The highly Ca-doped compounds undergo a superconducting phase transition under hydrostatic pressure ~ 3GPa, which is really intriguing since the hole-doped even-leg spin-ladder system was theoretically predicted as superconductors by charge-pairing mechanism through antiferromagnetic interaction on the rungs of spin ladders. In the previous study, we discovered that all compounds with different Ca content have a singlet ground state with a spin-gap ~ 32meV. In the highly Ca-doped sample SrCa13Cu24O41, a long-range magnetic ordering takes place at ~ 4.2K. Interestingly, the singlet spin-liquid state and the long-range magnetic ordering coexist in this compound. In this study, we further investigated its spin dynamics in the ordered phase by using inelastic neutron scattering on PELICAN and SIKA at OPAL. We observed the gapless spin-wave excitation, dispersive along the a and c axes but nondispersive along the b axis, indicating the nature of a 2D magnet. A dynamic model has been proposed to fit the experimental data, indicating three major exchange interactions along rungs (JR), legs (JL) and between neighbor ladders (JInter). This study helps us to understand the origin of the spin liquid ground state in this low-dimensional magnet, in which hole-doping should be attributed to induce the long-range magnetic ordering due to the disorder-induced order effect.