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Influence of interstitial Mn on magnetism in the room-temperature ferromagnet Mn1+δSb

Physical Review B 2015年第22期91卷 224418-224418页

作者： A. E. Taylor T. Berlijn S. E. Hahn A. F. May T. J. Williams L. Poudel S. Calder R. S. Fishman M. B. Stone A. A. Aczel H. B. Cao M. D. Lumsden A. D. Christianson Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Center for Nanophase Materials Sciences and Computer Science and Mathematics Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831-6494 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA

We report elastic and inelastic neutron-scattering measurements of the high-TC ferromagnet Mn1+δSb. Measurements were performed on a large, TC=434 K, single crystal with an interstitial Mn content of δ≈0.13. The neutron-diffraction results reveal that the interstitial Mn has a magnetic moment, and that it is aligned antiparallel to the main Mn moment. We perform density functional theory calculations including the interstitial Mn and find the interstitial to be magnetic, in agreement with the diffraction data. The inelastic neutron-scattering measurements reveal two features in the magnetic dynamics: (i) a spin-wave-like dispersion emanating from ferromagnetic Bragg positions (HK2n), and (ii) a broad, nondispersive signal centered at forbidden Bragg positions (HK2n+1). The inelastic spectrum cannot be modeled by simple linear spin-wave-theory calculations and appears to be significantly altered by the presence of the interstitial Mn ions. The results show that the influence of the interstitial Mn on the magnetic state in this system is more important than previously understood.

关键词： FERROMAGNETIC resonance MAGNETISM SINGLE crystals NEUTRON measurement MAGNETIC moments

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Depth data assisted structure-from-motion parameter optimization and feature track correction

Depth data assisted structure-from-motion parameter optimiza...

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Applied Imagery Pattern Recognition Workshop (AIPR)

作者： Shawn Recker Christiaan Gribble Mikhail M. Shashkov Mario Yepez Mauricio Hess-Flores Kenneth I. Joy Applied Technology Operation SURVICE Engineering Belcamp Maryland Institute of Data Analysis and Visualization University of California Davis Davis California

Structure-from-Motion (SfM) applications attempt to reconstruct the three-dimensional (3D) geometry of an underlying scene from a collection of images, taken from various camera viewpoints. Traditional optimization techniques in SfM, which compute and refine camera poses and 3D structure, rely only on feature tracks, or sets of corresponding pixels, generated from color (RGB) images. With the abundance of reliable depth sensor information, these optimization procedures can be augmented to increase the accuracy of reconstruction. This paper presents a general cost function, which evaluates the quality of a reconstruction based upon a previously established angular cost function and depth data estimates. The cost function takes into account two error measures: first, the angular error between each computed 3D scene point and its corresponding feature track location, and second, the difference between the sensor depth value and its computed estimate. A bundle adjustment parameter optimization is implemented using the proposed cost function and evaluated for accuracy and performance. As opposed to traditional bundle adjustment, in the event of feature tracking errors, a corrective routine is also present to detect and correct inaccurate feature tracks. The filtering algorithm involves clustering depth estimates of the same scene point and observing the difference between the depth point estimates and the triangulated 3D point. Results on both real and synthetic data are presented and show that reconstruction accuracy is improved.

关键词： Cameras Three-dimensional displays Cost function Image reconstruction Accuracy Solid modeling

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High-energy continuum of magnetic excitations in the two-dimensional quantum antiferromagnet Sr2CuO2Cl2

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Physical Review B 2014年第18期89卷 180410(R)-180410(R)页

作者： K. W. Plumb A. T. Savici G. E. Granroth F. C. Chou Young-June Kim Department of Physics University of Toronto Toronto Ontario Canada M5S 1A7 Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Center for Condensed Matter Sciences National Taiwan University Taipei 10617 Taiwan

We have measured the magnetic excitation spectrum of the model square-lattice spin-1/2 antiferromagnet Sr2CuO2Cl2 over a broad range of energies and momenta using high-resolution inelastic neutron scattering (INS). The magnon dispersion along the zone boundary was accurately measured to be a 43 meV between (1/2,0) and (3/4,1/4) indicating the importance of coupling beyond nearest neighbors in the spin Hamiltonian. We observe a strong momentum dependent damping of the zone-boundary magnons at (1/2,0) revealing a high-energy continuum of magnetic excitations. A direct comparison between our INS measurements and resonant inelastic x-ray scattering (RIXS) measurements shows that the RIXS spectrum contains significant contributions from higher energy excitations not previously considered. Our observations demonstrate that this high-energy continuum of magnetic fluctuations is an ubiquitous feature of insulating monolayer cuprates, apparent in both inelastic neutron and light scattering measurements.

关键词： ANTIFERROMAGNETIC materials QUANTUM theory NEUTRON scattering X-ray scattering SPECTRUM analysis

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Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffed Yb2Ti2O7

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Physical Review B 2015年第13期92卷 134420-134420页

作者： J. Gaudet D. D. Maharaj G. Sala E. Kermarrec K. A. Ross H. A. Dabkowska A. I. Kolesnikov G. E. Granroth B. D. Gaulin Department of Physics and Astronomy McMaster University Hamilton ON Canada L8S 4M1 Department of Physics Colorado State University Fort Collins Colorado 80523-1875 USA Brockhouse Institute for Materials Research Hamilton ON Canada L8S 4M1 Chemical and Engineering Materials Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Canadian Institute for Materials Research 180 Dundas Street West Toronto Ontario Canada M5G 1Z8

Time-of-flight neutron spectroscopy has been used to determine the crystalline electric field (CEF) Hamiltonian, eigenvalues and eigenvectors appropriate to the J=7/2 Yb3+ ion in the candidate quantum spin ice pyrochlore magnet Yb2Ti2O7. The precise ground state (GS) of this exotic, geometrically frustrated magnet is known to be sensitive to weak disorder associated with the growth of single crystals from the melt. Such materials display weak “stuffing,” wherein a small proportion, ≈2%, of the nonmagnetic Ti4+ sites are occupied by excess Yb3+. We have carried out neutron spectroscopic measurements on a stoichiometric powder sample of Yb2Ti2O7, as well as a crushed single crystal with weak stuffing and an approximate composition of Yb2+xTi2−xO7+y with x=0.046. All samples display three CEF transitions out of the GS, and the GS doublet itself is identified as primarily composed of mJ=±1/2, as expected. However, stuffing at low temperatures in Yb2+xTi2−xO7+y induces a similar finite CEF lifetime as is induced in stoichiometric Yb2Ti2O7 by elevated temperature. We conclude that an extended strain field exists about each local “stuffed” site, which produces a distribution of random CEF environments in the lightly stuffed Yb2+xTi2−xO7+y, in addition to producing a small fraction of Yb ions in defective environments with grossly different CEF eigenvalues and eigenvectors.

关键词： NEUTRON spectroscopy CRYSTALLINE electric field STOICHIOMETRY YTTERBIUM compounds HAMILTONIAN systems EIGENVALUES EIGENVECTORS

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High-energy magnetic excitations in overdoped La2−xSrxCuO4 studied by neutron and resonant inelastic x-ray scattering

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Physical Review B 2015年第18期91卷 184513-184513页

作者： S. Wakimoto K. Ishii H. Kimura M. Fujita G. Dellea K. Kummer L. Braicovich G. Ghiringhelli L. M. Debeer-Schmitt G. E. Granroth Quantum Beam Science Center Japan Atomic Energy Agency Tokai Ibaraki 319-1195 Japan SPring-8 Japan Atomic Energy Agency Hyogo 679-5148 Japan Institute of Multidisciplinary Research for Advanced Materials Tohoku University Sendai 980-8577 Japan Institute for Materials Research Tohoku University Katahira Sendai 980-8577 Japan CNR-SPIN and Dipartimento di Fisica Politenico di Milano Piazza Leonardo da Vinci 32 I-20133 Milano Italy European Synchrotron Radiation Facility 6 rue Jules Horowitz F-38043 Grenoble France Instrument and Source Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831USA Quantum Condensed Matter Division and Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

We have performed neutron inelastic scattering and resonant inelastic x-ray scattering (RIXS) at the Cu-L3 edge to study high-energy magnetic excitations at energy transfers of more than 100 meV for overdoped La2−xSrxCuO4 with x=0.25 (Tc=15 K) and x=0.30 (nonsuperconducting) using identical single-crystal samples for the two techniques. From constant-energy slices of neutron-scattering cross sections, we have identified magnetic excitations up to ∼250 meV for x=0.25. Although the width in the momentum direction is large, the peak positions along the (π,π) direction agree with the dispersion relation of the spin wave in the nondoped La2CuO4 (LCO), which is consistent with the previous RIXS results of cuprate superconductors. Using RIXS at the Cu-L3 edge, we have measured the dispersion relations of the so-called paramagnon mode along both (π,π) and (π,0) directions. Although in both directions the neutron and RIXS data connect with each other and the paramagnon along (π,0) agrees well with the LCO spin-wave dispersion, the paramagnon in the (π,π) direction probed by RIXS appears to be less dispersive and the excitation energy is lower than the spin wave of LCO near (π/2,π/2). Thus, our results indicate consistency between neutron inelastic scattering and RIXS, and elucidate the entire magnetic excitation in the (π,π) direction by the complementary use of two probes. The polarization dependence of the RIXS profiles indicates that appreciable charge excitations exist in the same energy range of magnetic excitations, reflecting the itinerant character of the overdoped sample. A possible anisotropy in the charge excitation intensity might explain the apparent differences in the paramagnon dispersion in the (π,π) direction as detected by the x-ray scattering.

关键词： X-ray scattering NEUTRONS ELECTROMAGNETIC waves SPIN excitations SPIN waves

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Frustrated fcc antiferromagnet Ba2YOsO6: Structural characterization, magnetic properties, and neutron scattering studies

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Physical Review B 2015年第7期91卷 075133-075133页

作者： E. Kermarrec C. A. Marjerrison C. M. Thompson D. D. Maharaj K. Levin S. Kroeker G. E. Granroth R. Flacau Z. Yamani J. E. Greedan B. D. Gaulin Department of Physics and Astronomy McMaster University Hamilton Ontario L8S 4M1 Canada Department of Chemistry McMaster University Hamilton Ontario L8S 4M1 Canada Department of Chemistry University of Manitoba Winnipeg Manitoba R3T 2N2 Canada Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Canadian Neutron Beam Centre AECL Chalk River Ontario K0J 1J0 Canada Brockhouse Institute for Materials Research Hamilton Ontario L8S 4M1 Canada Canadian Institute for Advanced Research 180 Dundas Street West Toronto Ontario M5G 1Z8 Canada

We report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2YOsO6. The Fm3¯m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ∼−700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN∼69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ∼3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. Time-of-flight inelastic neutron results reveal a large spin gap Δ∼17 meV, unexpected for an orbitally quenched, d3 electronic configuration. We discuss this in the context of the ∼5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ∼3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.

关键词： ANTIFERROMAGNETIC materials NEUTRON scattering BARIUM analysis MAGNETIC properties of metals TIME-of-flight spectrometry

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Quasi-two-dimensional spin and phonon excitations in La1.965Ba0.035CuO4

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Physical Review B 2015年第22期91卷 224404-224404页

作者： J. J. Wagman D. Parshall M. B. Stone A. T. Savici Y. Zhao H. A. Dabkowska B. D. Gaulin Department of Physics and Astronomy McMaster University Hamilton Ontario Canada L8S 4M1 NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Materials Sciences and Engineering University of Maryland College Park Maryland 20742 USA Brockhouse Institute for Materials Research McMaster University Hamilton Ontario Canada L8S 4M1 Canadian Institute for Advanced Research 180 Dundas St. W. Toronto Ontario Canada M5G 1Z8

We present time-of-flight inelastic neutron scattering measurements of La1.965Ba0.035CuO4 (LBCO), a lightly doped member of the high temperature superconducting La-based cuprate family. By using time-of-flight neutron instrumentation coupled with single crystal sample rotation we obtain a four-dimensional data set (three Q and one energy) that is both comprehensive and spans a large region of reciprocal space. Our measurements identify rich structure in the energy dependence of the highly dispersive spin excitations, which are centered at equivalent (12,12,L) wave vectors. These structures correlate strongly with several crossings of the spin excitations with the lightly dispersive phonons found in this system. These effects are significant and account for on the order of 25% of the total inelastic scattering for energies between ≈5 and 40 meV at low |Q|. Interestingly, this scattering also presents little or no L dependence. As the phonons and dispersive spin excitations centered at equivalent (12,12,L) wave vectors are common to all members of La-based 214 copper oxides, we conclude such strong quasi-two-dimensional scattering enhancements are likely to occur in all such 214 families of materials, including those concentrations corresponding to superconducting ground states. Such a phenomenon appears to be a fundamental characteristic of these materials and is potentially related to superconducting pairing.

关键词： PHONONS LANTHANUM compounds ELECTRONIC excitation SUPERCONDUCTIVITY TRANSITION metal compounds

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Highlights from the 5th Symposium on Biological data visualization: Part 2

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BMC proceedings 2015年第SUPPL 6 PROCEEDINGS OF THE 5TH SYMPOSIUM ON BIOLOGICAL DATA期9卷 S1页

作者： Jan Aerts G Elisabeta Marai Kay Nieselt Cydney Nielsen Marc Streit Daniel Weiskopf Visual Data Analysis Lab ESAT/STADIUS KU Leuven Kasteelpark Arenberg 10 3001 Leuven Belgium iMinds Medical IT KU Leuven Kasteelpark Arenberg 10 3001 Leuven Belgium. Electronic Visualization Lab University of Illinois at Chicago 851 S. Morgan St Chicago IL 60607 USA. Center for Bioinformatics University of Tübingen Sand 14 72076 Tübingen Germany. Department of Pathology and Laboratory Medicine University of British Columbia and British Columbia Cancer Agency 675 West 10th Avenue Vancouver British Columbia V5Z 1L3 Canada. Institute of Computer Graphics Johannes Kepler University Linz Altenberger Straße 69 4020 Linz Austria. VISUS University of Stuttgart Allmandring 19 70569 Stuttgart Germany.

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PhonMatrix: Visualizing co-occurrence constraints of sounds 51

PhonMatrix: Visualizing co-occurrence constraints of sounds

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51st Annual Meeting of the Association for Computational Linguistics, ACL 2013

作者： Mayer, Thomas Rohrdantz, Christian Research Unit Quantitative Language Comparison Philipps University of Marburg Data Analysis and Visualization Group University of Konstanz

This paper describes the online tool PhonMatrix, which analyzes a word list with respect to the co-occurrence of sounds in a specified context within a word. The co-occurrence counts from the user-specified context are statistically analyzed according to a number of association measures that can be selected by the user. The statistical values then serve as the input for a matrix visualization where rows and columns represent the relevant sounds under investigation and the matrix cells indicate whether the respective ordered pair of sounds occurs more or less frequently than expected. The usefulness of the tool is demonstrated with three case studies that deal with vowel harmony and similar place avoidance patterns. © 2013 Association for Computational Linguistics.

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Interaction Driven Subgap Spin Exciton in the Kondo Insulator SmB6

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Physical Review Letters 2015年第3期114卷 036401-036401页

作者： W. T. Fuhrman J. Leiner P. Nikolić G. E. Granroth M. B. Stone M. D. Lumsden L. DeBeer-Schmitt P. A. Alekseev J.-M. Mignot S. M. Koohpayeh P. Cottingham W. Adam Phelan L. Schoop T. M. McQueen C. Broholm Institute for Quantum Matter and Department of Physics and Astronomy The Johns Hopkins University Baltimore Maryland 21218 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA School of Physics Astronomy and Computational Sciences George Mason University Fairfax Virginia 22030 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Instrument Source Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA National Research Centre “Kurchatov Institute ” 123182 Moscow Russia National Research Nuclear University “MEPhI ” 115409 Moscow Russia Laboratoire Léon Brillouin CEA-CNRS CEA/Saclay 91191 Gif sur Yvette France Department of Chemistry The Johns Hopkins University Baltimore Maryland 21218 USA Department of Chemistry Princeton University Princeton New Jersey 08540 USA Department of Materials Science and Engineering The Johns Hopkins University Baltimore Maryland 21218 USA

Using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator SmB6 and describe its relation to the low energy insulating band structure. The resonant intensity is confined to the X and R high symmetry points, repeating outside the first Brillouin zone and dispersing less than 2 meV, with a 5d-like magnetic form factor. We present a slave-boson treatment of the Anderson Hamiltonian with a third neighbor dominated hybridized band structure. This approach produces a spin exciton below the charge gap with features that are consistent with the observed neutron scattering. We find that maxima in the wave vector dependence of the inelastic neutron scattering indicate band inversion.

关键词： INTERACTION model (Communication) NEUTRON scattering BRILLOUIN scattering EXCITON theory INELASTIC neutron scattering

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