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Search Publications

NIST Authors in Bold

Displaying 776 - 800 of 902

Phonon softening and anomalous mode near the x c = 0.5 quantum critical point inCa 2-x Sr x RuO 4

May 4, 2009
Author(s)
R. G. Moore, M. D. Lumsden, M. B. Stone, Jiandi Zhang, Ying Chen, Jeffrey Lynn, R. Jin, D Mandrus, E. W. Plummer
Inelastic neutron scattering is used to measure the temperature-dependent phonon dispersion in Ca2−xSrxRuO4(x=0.4,0.6). The in-plane Σ4 octahedral tilt mode softens significantly at the zone boundary of the high-temperature tetragonal (HTT) I41/acd

Itinerant spin excitations near the hidden order transition in URu2Si2

April 22, 2009
Author(s)
J. A. Janik, H. D. Zhou, Y.-J. Jo, L. Balicas, G. J. MacDougall, G. M. Luke, J. D. Garrett, K. J. McClellan, E. D. Bauer, J. L. Sarrao, Yiming Qiu, John R. Copley, Z. Yamani, W. J. Buyers, C. R. Wiebe
By means of neutron scattering we show that the high-temperature precursor to the hidden order state of the heavy fermion superconductor URu 2Si 2 exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of

Measuring 6LI(N,T) and 10B(N,A) Cross Sections Using the NIST Alpha-Gamma Device

April 15, 2009
Author(s)
Maynard S. Dewey, David M. Gilliam, Jeffrey S. Nico, G.L. Green, A. Laptev, A. Yue
The 6LI(N,T) and 10B(N,A) cross sections are important neutron cross section standards. Precise knowledge of these cross sections is essential because they are often used as reference standards for obtaining the neutron fluence in investigations of the

A New Evaluation of the Half-life of 241Pu

April 14, 2009
Author(s)
Roger Wellum, Andre Verbruggen, Ruediger Kessel
A new evaluation of the half-life of 241Pu has been made by developing earlier methods and techniques and employing further measurements of the isotopic ratio of an initially enriched 241Pu material. A correction to the previous value has had to be made

International NMR-based Environmental Metabolomics Intercomparison Exercise

April 7, 2009
Author(s)
Daniel W. Bearden, Mark Viant, Jacob Bundy, Ian Burton, Tim Collette, Drew Ekman, Tobias Karakach, Ching Y. Lin, Simone Rochfort, Jeff de Ropp, Quincy Teng, Ron Tjeerdema, John Walter, Huifeng Wu
Several fundamental requirements must be met so that NMR-based metabolomics can be formally adopted into environmental monitoring and chemical risk assessment. Here we report an intercomparison exercise which has evaluated the accuracy, precision and

Use of Neutron Imaging for PEMFC Performance Analysis and Design

March 1, 2009
Author(s)
T Trabold, Jon P. Owejan, Jeffrey J. Gagliardo, David L. Jacobson, Daniel S. Hussey, Muhammad D. Arif
Efficient water management is one of the key design objectives for proton exchange membrane fuel cells (PEMFCs), due to the influence of water on material selection, hardware configuration, and stack operating conditions. Neutron imaging has proven to be

Study of hydrogen diffusion in superprotonic ionic conductors, MHXO4, by m+SR and QENS

February 21, 2009
Author(s)
Yutaka Ikedo, Hiroshi Nozaki, Masashi Harada, Jun Sugiyama, Taku J. Sato, Yasumitsu Matsuo, Kusuo Nishiyama, James S. Lord, Yiming Qiu, John R. Copley
In order to clarify the mechanism of high proton conductivity (σH+) for superprotonic ionic conductors, MHXO4, where M=Cs and Rb, X=S and Se, muon-spin rotation and relaxation (μ+SR) and quasi-elastic neutron scattering (QENS) measurements have been

Surface Dynamics of "Dry" Homopolymer Brushes

February 10, 2009
Author(s)
Bulent Akgun, Gokce Ugur, Jianqiang Zhang, Suresh Narayanan, Sanghoon Song, Heegu Lee, William J. Brittain, Hyunjung G. Kim, Sunil K. Sinha, Mark Foster
The dynamics of the surface height fluctuations on layers of covalently tethered, nearly monodisperse polymer chains synthesized by atom transfer radical polymerization were studied using x-ray photon correlation spectroscopy. The data reveal that both

Pulse Shape Discrimination for a Fast Neutron Detector

February 9, 2009
Author(s)
Kevin J. Coakley, Dominic F. Vecchia, Jeffrey S. Nico, B Fisher
We are developing a detector that uses liquid scintillator loaded with Li-6 for the efficient measurement of fast neutrons and their energy. Such a detector would have both scientific applications such as quantification of neutron energy spectra in

Radiative Beta Decay of the Free Neutron

February 2, 2009
Author(s)
R L. Cooper, T E. Chupp, Maynard S. Dewey, Thomas R. Gentile, Hans Pieter Mumm, Jeffrey S. Nico, Alan Keith Thompson, B M. Fisher, I Kremsky, F E. Wietfeldt, E J. Beise, H Breuer, K G. Kiriluk, J Bryne, Kevin Coakley, Changbo Fu
The theory of quantum electrodynamics predicts that the beta decay of the neutron into a proton, electron, and antineutrino is accompanied by a continuous spectrum of emitted photons described as inner bremsstrahlung. While this phenomenon has been

Structure and Degeneracy of Vortex Lattice Domains in Pure Superconducting Niobium: A Small-Angle Neutron Scattering Study

January 27, 2009
Author(s)
Mark Laver, E M. Forgan, C Bowell, C D. Dewhurst, S Ramos, A B. Abrahamsen, D. K. Christen, D Fort, S Muhlbauer, J Kohlbrecher, R Cubitt
High-purity niobium exhibits a surprisingly rich assortment of vortex lattice (VL) structures for fields applied parallel to a fourfold symmetry axis, with all observed VL phases made up of degenerate domains that spontaneously break some crystal symmetry

3:1 Magnetization Plateau and Suppression of Ferroelectric Polarization in an Ising Chain Multiferroic

January 26, 2009
Author(s)
Y.-J. Jo, Seoungsu Lee, E. Choi, H. Yi, William D. Ratcliff, Y. Choi, V. Kiryukhin, S.-W. Cheong, L. Balicas
Ferroelectric Ising chain magnet Ca3Co2−xMnxO6 (x≃0.96) was studied in magnetic fields of up to 33 T. Magnetization and neutron-scattering measurements reveal successive metamagnetic transitions from the zero-field ↑↑↓↓ spin configuration to the ↑↑↑↓ state

Origin and Tuning of the Magnetocaloric Effect in the Magnetic Refrigerant Mn1.1Fe0.9(P0.8Ge0.2)

January 26, 2009
Author(s)
Danmin Liu, Ming Yue, Jiuxing Zhang, T. M. McQueen, Jeffrey Lynn, Xiaolu Wang, Ying Chen, Jiying Li, R. J. Cava, X. Liu, Zaven Altounian, Qingzhen Huang
Neutron-diffraction and magnetization measurements have been carried out on a series of samples of the magnetorefrigerant Mn1+yFe1−yP1−xGex. The data reveal that the ferromagnetic and paramagnetic phases correspond to two very distinct crystal structures

Spin Correlations in the Geometrically Frustrated Pyrochlore Tb 2 Mo 2 O 7

December 31, 2008
Author(s)
D. K. Singh, J. S. Helton, S. Chu, T. Han, C. Bonnoit, Sung Chang, Hye J. Kang, Jeffrey W. Lynn, Y. S. Lee
We report neutron scattering studies of the spin correlations of the geometrically frustrated py- rochlore Tb 2Mo 2O 7using single crystal samples. Elastic diffuse peaks are observed at low temperatures, indicating short-range ordering of the Tb 3+ moments

Neutron-Diffraction Measurements of Magnetic Order and a Structural Transition in the Parent BaFe2As2 Compound of FeAs-Based High-Temperature Superconductors

December 17, 2008
Author(s)
Qingzhen Huang, Yiming Qiu, Wei Bao, Mark Green, Jeffrey Lynn, Y. C. Gasparovic, T. Wu, G. Wu, X. H. Chen
The recent discovery of superconductivity in (Ba,K)Fe2As2, which crystallizes in the ThCr2Si2 (122) structure as compared with the LnFeAsO (Ln is lanthanide) systems that possess the ZrCuSiAs (1111) structure, demonstrates the exciting potential of the

Neutron Transmission of Single-Crystal Magnesium Fluoride

November 27, 2008
Author(s)
John Barker, David F. Mildner, Jose Rodriguez Rivera, P. Thiyagarajan
The neutron attenuation through single-crystal magnesium fluoride has been measured as a function of wavelength at both room temperature and 77 K. These data confirm a total cross section that is lower than MgO for wavelengths greater than 0.2 nm. MgF 2

Pressure-induced volume-collapsed tetragonal phase of CaFe 2 As 2 as seen via neutron scattering

November 24, 2008
Author(s)
A. Kreyssig, Mark Green, Y. Lee, G. D. Samolyuk, Pawel Zajdel, Jeffrey Lynn, S. L. Bud'ko, M. S. Torikachvili, N. Ni, S. Nandi, Juscelino Leao, Sarah Poulton, D. N. Argyriou, B. N. Harmon, R. J. McQueeny, P. C. Canfield, A. I. Goldman
Recent investigations of the superconducting iron-arsenide families have highlighted the role of pressure, be it chemical or mechanical, in fostering superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced transition to a nonmagnetic

Unusual Heavy-mass Nearly Ferromagnetic State with a Surprisingly Large Wilson Ratio in Double Layered Ruthenates (Sr 1-x Ca x ) 3 Ru 2 O 7

November 14, 2008
Author(s)
Z Qu, L Spinu, H Q. Yuan, V Dobrosavljevic, Wei Bao, Jeffrey Lynn, M Nicklas, J Peng, T J. Liu, F Fobes, E Flesch, Z Q. Mao
We report a very unusual heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio Rw (e.g., Rw 700 for x = 0.2) in double layered ruthenates (Sr 1- xCa x) 3Ru 2O 7. This state does not evolve into a long-range ferromagnetic order

Phase and Valence Transitions in Ba^2^LnSn x Nb 1-x O 6-d

November 1, 2008
Author(s)
Paul J. Saines, Brendan J. Kennedy, Bernt Johannessen, Sarah Poulton
The structures of compounds in the perovskite series Ba2LnSnxNb1−xO6−δ (Ln=Pr and Tb and x=0, 0.1, 0.2, ..., 1.0) have been examined using synchrotron X-ray and neutron diffraction. It was found that niobate members of both series feature full B-site

Structural and magnetic phase diagram of CeFeAsO1- xFx and its relation to high-temperature superconductivity

October 26, 2008
Author(s)
Jun Zhao, Qingzhen Huang, Clarnia dela Cruz, Shiliang Li, Jeffrey Lynn, Ying Chen, Mark Green, G. F. Chen, Z. C. Li, J. L. Luo, N. L. Wang, Pengcheng Dai
Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO1−xFx (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO1−xFx as
Displaying 776 - 800 of 902
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