Browsing by Author "Zhao, Y"
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- ItemANSTO heavy ion ToF for analysis of light elements in thin films(Australian Institute of Nuclear Science and Engineering (AINSE), 2007-11) Ionescu, M; Zhao, Y; Siegele, R; Cohen, DD; Lynch, D; Garton, DB; Stelcer, E; Prior, MJThin films have various potential applications in electronic devices, and their performance is intricately linked with the electric and magnetic properties of the film, in which an important role is played by the presence of light elements, in particular Hydrogen, Oxygen and Nitrogen. The source of light elements, the form in which they are incorporated into the thin film, and how this is influencing the MgB2 thin film properties is currently under scrutiny by various research groups. Typically these films are grown on oxide ceramic substrates, such as Al2O3-C and it is possible that the source of Oxygen is the substrate itself or the growth atmosphere. Here we report on a study of light elements in MgB2 thin films grown on various substrates, using heavy ions recoil and a time-of-flight detector. A series of MgB2 thin film samples produced by PLD (pulsed laser deposition) were analyzed, including films produced in-situ on Al2O3-C substrates with an on-axis and off-axis geometry, one film produced in-situ with an off-axis geometry, and one film produced ex-situ, with a bulk-like Tc. We also analyzed one film produced with on-axis geometry under the same conditions on Si (001) substrate. The amount of Oxygen detected by ToF, appears to be correlated with the Tc of the films, the higher the Tc the lower the oxygen content. Also, the superconducting properties of the examined thin films are discussed in the context of the results.
- ItemComplex 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, HMonoclinic 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.
- ItemErratum: Magnetic structure and dzyaloshinskii-moriya interaction in the S=1/2 helical-honeycomb antiferromagnet α−Cu2V2O7 [Phys. Rev. B 92, 024423 (2015)](American Physical Society, 2017-03-10) Gitgeatpong, G; Zhao, Y; Avdeev, M; Piltz, RO; Sato, TJ; Matan, KNo abstract available. See the original item at: https://apo.ansto.gov.au/dspace/handle/10238/10250
- ItemHeavy ion ToF analysis of oxygen incorporation in MgB2 thin films(Elsevier, 2008-04) Ionescu, M; Zhao, Y; Siegele, R; Cohen, DD; Stelcer, E; Prior, MJOxygen incorporation in MgB2 thin films during their fabrication process has a strong influence on the future properties of the films, and was studied by Elastic Recoil Detection Analysis with heavy ions and a time-of-flight detection. A series of MgB2 thin film samples were analyzed, including films produced in situ on Al2O3-C and Si (0 0 1) substrates (with higher Tc and lower Tc) with an “on-axis” geometry, and films produced in situ with an “off-axis” geometry. The amount of oxygen detected in these films appears to be correlated with the Tc of the films, the higher the Tc the lower the oxygen content. The superconducting properties of the examined thin films are discussed in the context of the ERDA results. © 2008, Elsevier Ltd.
- ItemMagnetic field splitting of the spin resonance in CeCoIn5(American Physical Society, 2012-10-17) Stock, C; Broholm, C; Zhao, Y; Demmel, F; Kang, HJ; Rule, KC; Petrovic, CNeutron scattering in strong magnetic fields is used to show the spin resonance in superconducting CeCoIn(5) (T(c) = 2.3 K) is a doublet. The underdamped resonance ((h) over bar Gamma = 0.069 +/- 0.019 meV) Zeeman splits into two modes at E(+/-) = (h) over bar Omega(0) +/- mu(B mu 0)H with alpha = 0.96 +/- 0: 05. A linear extrapolation of the lower peak reaches zero energy at 11.2 +/- 0.5 T, near the critical field for the incommensurate "Q phase." Kenzelmann et al. [Science 321, 1652 (2008)] This, taken with the integrated weight and polarization of the low-energy mode (E(-)), indicates that the Q phase can be interpreted as a Bose condensate of spin excitons. © 2012, American Physical Society.
- ItemMagnetic properties and magnetic structure of the frustrated quasi-one-dimensional antiferromagnet SrCuTe2O6(American Physical Society, 2020-10-07) Saeaun, P; Zhao, Y; Piyawongwatthana, P; Sato, TJ; Chou, FC; Avdeev, M; Gitgeatpong, G; Matan, KMagnetization measurements on single-crystal cubic SrCuTe2O6 with an applied magnetic field along three inequivalent high symmetry directions [100], [110], and [111] reveal weak magnetic anisotropy. The fits of the magnetic susceptibility to the result from a quantum Monte Carlo simulation on the Heisenberg spin-chain model, where the chain is formed via the dominant third-nearest-neighbor exchange interaction J3, yield the intrachain interaction (J3/kB) between 50.12(7) K for the applied field along [110] and 52.5(2) K along [100] with about the same g factor of 2.2. Single-crystal neutron diffraction unveils the transition to the magnetic ordered state as evidenced by the onset of the magnetic Bragg intensity at TN1=5.25(9)K with no anomaly of the second transition at TN2 reported previously. Based on irreducible representation theory and magnetic space group analysis of powder and single-crystal neutron diffraction data, the magnetic structure in the Shubnikov space group P4132, where the Cu2+S=1/2 spins antiferromagnetically align in the direction perpendicular to the spin chain, is proposed. The measured ordered moment of 0.52(6)μB, which represents 48% reduction from the expected value of 1μB, suggests the remaining influence of frustration resulting from the J1 and J2 bonds. ©2020 American Physical Society
- ItemMagnetic properties of the S = 1/2 antiferromagnetic spin-chain α - Cu2V2O7(American Physical Society, 2015-03-06) Gitgeatpong, G; Zhao, Y; Avdeev, M; Piltz, RO; Sato, TJ; Matan, KMagnetic properties of the S = 1 / 2 antiferromagnetic spin-chain, α - Cu2V2O7, have been studied using magnetization and neutron scattering measurements on powder and single-crystal samples. Magnetic susceptibility reveals a Curie-Weiss temperature of Θ = -73.2(9) K with a magnetic phase transition at TN = 33 K while the Bonner-Fisher fit to the magnetic susceptibility for T >TN with magnetic field perpendicular to the crystallographic a - axis yields the intra-chain coupling of |J|/k = 46.0(2) K. Small ferromagnetism below TN is due to spin-canting caused by Dzyaloshinskii-Moriya interactions. Analysis of the neutron diffraction data reveals that the Cu2+ spins are coupled antiferromagnetically along zigzag chains, which run alternately along [011] and [01-1] directions. The ordered moment of 0.925(3) μB is predominantly along the a - axis. Our recent inelastic neutron scattering, which reveals atypical magnetic excitations centered at commensurate wave vectors (0, +/-0.25, 0) around the magnetic zone center, will also be discussed. © 2021 American Physical Society
- ItemMagnetic structure and dzyaloshinskii-moriya interaction in the S=12 helical-honeycomb antiferromagnet α−Cu2V2O7(American Physical Society, 2015-07-23) Gitgeatpong, G; Zhao, Y; Avdeev, M; Piltz, RO; Sato, TJ; Matan, KMagnetic properties of the S=12 antiferromagnet α−Cu2V2O7 have been studied using magnetization, quantum Monte Carlo (QMC) simulations, and neutron diffraction. Magnetic susceptibility shows a broad peak at ∼50K followed by an abrupt increase indicative of a phase transition to a magnetically ordered state at TN=33.4(1) K. Above TN, a fit to the Curie-Weiss law gives a Curie-Weiss temperature of Θ=−73(1) K suggesting the dominant antiferromagnetic coupling. The result of the QMC calculations on the helical-honeycomb spin network with two antiferromagnetic exchange interactions J1 and J2 provides a better fit to the susceptibility than the previously proposed spin-chain model. Two sets of the coupling parameters J1:J2=1:0.45 with J1=5.79(1) meV and 0.65:1 with J2=6.31(1) meV yield equally good fits down to ∼TN. Below TN, weak ferromagnetism due to spin canting is observed. The canting is caused by the Dzyaloshinskii-Moriya interaction with an estimated bc-plane component |Dp|≃0.14J1. Neutron diffraction reveals that the S=12Cu2+ spins antiferromagnetically align in the Fd′d′2 magnetic space group. The ordered moment of 0.93(9) μB is predominantly along the crystallographic a axis. ©2015 American Physical Society
- ItemRadiocarbon variations from the Southern Hemisphere, 10,350–9700 cal BP(Elsevier, 2004-08) Barbetti, M; Hua, Q; Zoppi, U; Fink, D; Zhao, Y; Thomson, BWe have made AMS measurements on a series of 10-ring samples from a subfossil Huon pine log found in western Tasmania (42°S, 145°E). The results show a pronounced rise in Δ14C over the first 200 years, and a decrease over the following 160 years. Tree-ring width measurements indicate that this log (catalogue SRT-447) can be cross-dated with another subfossil log (SRT-416) for which a series of high-precision radiometric 14C measurements have previously been made. When the two tree-ring series are thus aligned, SRT-447 is the older of the two logs, and there is a 139-year overlap. We then have a Huon pine floating chronology spanning 680 years, with 14C measurements attached. The 14C data sets agree well within the period of overlap indicated by the tree-rings. The 14C variations from Huon pine show excellent agreement with those from German oak and pine for the period 10,350–9670 cal BP. Aligning the Huon pine 14C series with that from German oak and pine allows us to examine the inter-hemispheric offset in 14C dates in the early Holocene. © 2004 Elsevier B.V.
- ItemSodium 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, FCThe 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
- ItemSpectroscopic identification of hydrogen spillover species in ruthenium-modified high surface area carbons by diffuse reflectance infrared fourier transform spectroscopy(American Chemical Society., 2012-12-27) Blackburn, JL; Engtrakul, C; Bult, JB; Hurst, K; Zhao, Y; Xu, Q; Parilla, PA; Simpson, LJ; Rocha, JDR; Hudson, MR; Brown, CM; Gennett, TIn recent years, carbon-based sorbents have been recognized for their potential application within vehicular hydrogen storage applications. One method by which sorbents have been reported to store appreciable hydrogen at room temperature is via a spillover process: where molecular hydrogen is first dissociated by metal nanoparticle catalysts and atomic hydrogen subsequently migrates onto the carbon substrate. Many reports have invoked the spillover mechanism to explain enhancements in reversible room temperature hydrogen uptake for metal-decorated sorbents. However, there is a lack of experimental evidence for the proposed chemical species formed as well as several differing theoretical explanations describing the process. In this report, we utilize diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify the various chemical species formed upon room temperature H-2 charging of ruthenium-decorated high surface area carbons. Room temperature H-2 loading of a control sample with no ruthenium nanoparticles (Ru NPs) leads to broad reversible peaks in the DRIFTS spectrum that correspond to the vibration-rotation transitions of weakly bound physisorbed hydrogen molecules. In contrast, the sample modified with Ru NPs shows a variety of reversible and irreversible peaks in addition to the physisorbed H-2 peaks. Rigorous experimental and theoretical analysis enables the assignment of the peaks to ruthenium-mediated formation of water, surface hydroxyl groups (R-OH, where R = carbon or ruthenium), and C-H bonds. The low-energy DRIFTS peaks assigned to spillover C-H bonds were additionally confirmed using inelastic neutron spectroscopy. Reversible vibrational peaks consistent with ruthenium-mediated formation of C-H bonds provide much-needed spectroscopic evidence for the spillover process. The results demonstrated here should facilitate future mechanistic investigations of hydrogen sorption on transition metal nanoparticles and high surface area activated carbons. © 2012, American Chemical Society.
- ItemStudy of oxygen incorporation in PLD MgB2 films by Rutherford backscattering spectroscopy(Institute of Electrical and Electronics Engineers (IEEE), 2007-06) Zhao, Y; Ionescu, M; Dou, SX; Liu, HKThe Rutherford backscattering (RBS) method has been employed to study the incorporation of oxygen into MgB2 films during their fabrication by pulsed-laser deposition (PLD). A series of MgB2 thin film samples were analyzed, including two films produced in situ on Al2O3 - c substrates (with higher T-c and lower T-c) with an on-axis geometry, one film produced in situ with an off-axis geometry, and one film produced ex situ, with a bulk-like T-c. The amount of oxygen detected by RBS, which is stable in the form of MgO, appears to be correlated with the T-c of the films, the higher the T-c the lower the oxygen content. The superconducting properties of the thin films are discussed in the context of the RBS results. © 2007, Institute of Electrical and Electronics Engineers (IEEE)
- ItemSuperconducting and microstructural properties of two types of MgB/sub 2/ films prepared by pulsed laser deposition(Institute of Electrical and Electronics Engineers, 2005-06) Zhao, Y; Ionescu, M; Roussel, M; Pan, AV; Horvat, J; Dou, SXSignificant differences in superconducting and microstructural properties between two types of MgB2 films prepared by pulsed laser deposition were determined. A very high Hc2 - T slope of 1.1 T/K was achieved in the in situ film. The Jc - H curves of the in situ film also show a much weaker field dependence than that of the ex situ film. The magneto-optical (MO) images show that at 4 K the flux penetrates the in situ MgB2 film through random paths, while for the ex situ film, the flux penetration pattern is mostly repeatable, indicating a defect-controlled flux penetration. Microstructural study (transmission electron microscopy and atomic force microscopy) revealed a relatively big grain size in the ex situ film. The correlation between the superconducting properties, microstructure and preparation conditions is discussed with regard to the two types of films. © 2005 IEEE.