Browsing by Author "Wang, M"
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- ItemElectron doping evolution of the anisotropic spin excitations in BaFe(2-x)NixAs2(Americal Physical Society, 2012-07-10) Luo, HQ; Yamani, Z; Chen, YC; Lu, XY; Wang, M; Li, SL; Maier, TA; Danilkin, SA; Adroja, DT; Dai, PCWe use inelastic neutron scattering to systematically investigate the Ni-doping evolution of the low-energy spin excitations in BaFe(2-x)NixAs2 spanning from underdoped antiferromagnet to overdoped superconductor (0.03 <= x <= 0.18). In the undoped state, BaFe2As2 changes from paramagnetic tetragonal phase to orthorhombic antiferromagnetic (AF) phase below about 138 K, where the low-energy (<=similar to 80 meV) spin waves form transversely elongated ellipses in the [H, K] plane of the reciprocal space. Upon Ni doping to suppress the static AF order and induce superconductivity, the c-axis magnetic exchange coupling is rapidly suppressed and the momentum distribution of spin excitations in the [H, K] plane is enlarged in both the transverse and longitudinal directions with respect to the in-plane AF ordering wave vector of the parent compound. As a function of increasing Ni-doping x, the spin excitation widths increase linearly but with a larger rate along the transverse direction. These results are in general agreement with calculations of dynamic susceptibility based on the random phase approximation (RPA) in an itinerant electron picture. For samples near optimal superconductivity at x approximate to 0.1, a neutron spin resonance appears in the superconducting state. Upon further increasing the electron doping to decrease the superconducting transition temperature T-c, the intensity of the low-energy magnetic scattering decreases and vanishes concurrently with vanishing superconductivity in the overdoped side of the superconducting dome. Comparing with the low-energy spin excitations centered at commensurate AF positions for underdoped and optimally doped materials (x <= 0.1), spin excitations in the overdoped side (x = 0.15) form transversely incommensurate spin excitations, consistent with the RPA calculation. Therefore, the itinerant electron approach provides a reasonable description to the low-energy AF spin excitations in BaFe(2-x)NixAs2. © 2012, American Physical Society.
- 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.
- ItemMagnetic 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, MWe 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
- ItemNeutron scattering studies on ionic diffusion behaviors of superionic α-Cu2−δ Se(AIP Publishing, 2022-10-10) Li, L; Liu, H; Avdeev, M; Yu, DH; Danilkin, SA; Wang, MWe present studies on crystal structure and ionic diffusion behaviors of superionic Cu2−δ Se (δ = 0, 0.04, and 0.2) by utilizing neutron powder diffraction and quasi-elastic neutron scattering. In the superionic phase, the structural model with Cu ions occupying the Wyckoff sites of 8c and 32f provides the best description of the structure. As the content of Cu increasing in Cu2−δ Se, the Cu occupancy increases on the 32f site but decreases on the 8c site. Fitting to the quasi-elastic neutron scattering spectra reveals two diffusion modes: the localized diffusion between the 8c and 32f sites and the long-range diffusion between the adjacent 8c sites using the 32f site as a bypass. Between 430 and 650 K, we measured that the compound with more Cu content exhibits a larger long-range diffusion coefficient. Temperature in this range does not affect the long-range diffusion process obviously. Our results suggest the two diffusion modes cooperative and, thus, provide a microscopic understanding of the ionic diffusion of the Cu ions in superionic Cu2−δ Se. © 2024 AIP Publishing LLC
- ItemA novel multi-scale modelling approach for determining the bulk properties of difficult-to-characterise composites(Australian Institute of Physics, 2013-02-05) Mignone, PJ; Wang, M; Finlayson, TR; Echlin, MP; Mottura, A; Pollock, TM; Riley, DP; Franks, GVA multi-scale modelling approach is presented for determining the bulk properties of copper-infiltrated Tungsten (W-Cu). A three-dimensional (3D) data-set of the W-Cu microstructure was generated using a novel serial-sectioning instrument. The image data were then reconstructed into a 3D Finite Element (FE) mesh. This made it possible to determine the bulk properties of W-Cu by simulating a representative volume of the microstructure.
- ItemThree-dimensional characterization of the permeability of W–Cu composites using a new “triBeam” technique(Elsevier, 2014-02) Echlin, MP; Mottura, A; Wang, M; Mignone, PJ; Riley, DP; Franks, GV; Pollock, TMLarge three-dimensional microstructural datasets have been gathered for two W–Cu composites of 10 and 15 wt.% Cu using the TriBeam system via in situ femtosecond laser sectioning in a scanning electron microscope. Laser ablation was performed on W–Cu samples along a 90 ° edge, milling parallel with the imaging surface. Secondary electron images for 1000 two-dimensional slices were segmented into binary images representing Cu and W components using EM/MPM (expectation–maximization/maximization of the posterior marginals) image-processing algorithms. A statistically random volume sampling approach has been employed to evaluate the microstructural and property volume element sizes necessary for the assessment of volume fraction, surface-area to volume ratio and permeability, respectively. This approach also characterizes the mean values and variability in microstructure and properties for volume elements ranging from 10 μm to 160 μm on edge. The converged values of the volume fractions of Cu closely match experimental values measured by the Archimedes technique.© 2013 Acta Materialia Inc.