Browsing by Author "Winn, B"

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    Spin exchange optical pumping based polarized He-3 filling station for the hybrid spectrometer at the spallation neutron source
    (American Institute of Physics, 2013-06-01) Jiang, CY; Tong, X; Brown, DR; Culbertson, H; Graves-Brook, MK; Hagen, ME; Kadron, B; Lee, WT; Robertson, JL; Winn, B
    The Hybrid Spectrometer (HYSPEC) is a new direct geometry spectrometer at the Spallation Neutron Source at the Oak Ridge National Laboratory. This instrument is equipped with polarization analysis capability with 60 degrees horizontal and 15 degrees vertical detector coverages. In order to provide wide angle polarization analysis for this instrument, we have designed and built a novel polarized He-3 filling station based on the spin exchange optical pumping method. It is designed to supply polarized He-3 gas to HYSPEC as a neutron polarization analyzer. In addition, the station can optimize the He-3 pressure with respect to the scattered neutron energies. The depolarized He-3 gas in the analyzer can be transferred back to the station to be repolarized. We have constructed the prototype filling station. Preliminary tests have been carried out demonstrating the feasibility of the filling station. Here, we report on the design, construction, and the preliminary results of the prototype filling station. © 2013, American Institute of Physics.
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    Stripy order in buckled honeycomb lattice antiferromagnet Ba2NiTeO6
    (International Conference on Neutron Scattering, 2017-07-12) Asai, S; Soda, M; Kasatani, K; Ono, T; Avdeev, M; Garlea, VO; Winn, B; Masuda, T
    Ba NiTeO is a rare experimental realization of a buckled honeycomb lattice antiferromagnet. The nearest-neighbor and next-nearest-neighbor interactions in the honeycomb lattice are comparative due to the buckled geometry, leading to magnetic frustration. A magnetic transition is observed at 8.6 K in the susceptibility and heat capacity measurements [1]. The frustration parameter /T is 18.6, where is Weiss temperature and is the magnetic transition temperature. In order to investigate the low temperature state we performed neutron scattering experiments. In the diffraction profile magnetic Bragg peaks are observed at < , and the propagation vector is identified as (0, 1/2,1). Combination of the representation analysis and Rietveld refinement reveals that a collinear stripy structure [2] is realized [3]. Our calculation suggests that the stabilization of the stripy structure instead of spiral structure is ascribed to the competition between magnetic frustration and easy-axis type anisotropy. In the inelastic neutron spectrum at 2 K a magnetic excitation with an energy gap of 2 meV is observed. Spin-wave calculation based on two-dimensional frustrated honeycomb lattice antiferromagnet having easy-axis anisotropy reproduces the experimental data. The obtained parameters are consistent with Weiss temperature estimated from the bulk magnetic susceptibility measurement.