Four-circle single-crystal neutron diffractometer at the High Flux Isotope Reactor

Abstract

A four‐circle neutron diffractometer with a new multi‐wafer 331 Si monochromator has been installed and commissioned on a thermal beamline at the High Flux Isotope Reactor at Oak Ridge National Laboratory. The instrument is well suited to studies of nuclear and magnetic structures as a function of composition and temperature, resolving symmetry changes (lattice distortions and local structural changes), mapping the evolution of complex magnetic phases, determining hydrogen bonding, analyzing nuclear and spin densities, mapping diffuse scattering, and exploring fiber diffraction. Three incident wavelengths are available, 1.000, 1.536 and 2.540 Å, with intensities of 2.5 × 106, 2.2 × 107 and 8.0 × 106 neutrons cm−2 s−1, respectively. Either high‐resolution or high‐intensity modes are possible by horizontal bending of the monochromator. With increased bending of the monochromator, the incident flux on the sample passes through a maximum, increasing by ×2.0 for 1.000 Å, by ×3.5 for 1.536 Å and by ×3.5 for 2.540 Å, as compared to the flat condition. The flux increases because the lattice strain in the silicon crystals increases. The ω‐scan peak width increases with monochromator curvature and this width versus scattering angle flattens. Given these effects, the monochromator bending can be adjusted to deliver high intensity primarily for crystal structure refinements or high resolution for resolving symmetry changes. In addition to the traditional step‐scanning mode, a more efficient continuous‐scanning mode was developed, and both these are implemented through a LabView‐based control program, i.e. a modified version of the SPICE software package. A 4 K closed‐cycle helium refrigerator is permanently mounted on the χ‐circle of the goniometer to provide temperature control between 4 and 450 K.

Role of magnetism in superconductivity ofBaFe2As2: Study of5dAu-doped crystals

“…The neutron wavelength of 1.542 Å was used from a Si-220 monochromator. 44 Results are shown in Fig. 5a and b.…”

Low-temperature crystal and magnetic structure ofα−RuCl3

“…Single crystal neutron diffraction was performed at the HB-3A Fourcircle Diffractometer equipped with a 2D detector at the High Flux Isotope Reactor(HFIR) at ORNL. Neutron wavelengths of 1.005Å and 1.546Å were used from a bent perfect Si-331 and Si-220 monochromator [42]. Neutrons with a short wavelength of 1.005Å enabled a large reciprocal space coverage and were used to measure the nuclear structure.…”

Complex magnetic phase diagram with multistep spin-flop transitions in La0.25Pr0.75CoTan1, Garlea2, Kovnir3 et al. 2017Phys. Rev. BSelf Cite10130View full textAdd to dashboardCite

“…Powder and single-crystal neutron diffraction experiments on La 0.25 Pr 0.75 Co 2 P 2 were carried out using the HB-2A high-resolution powder diffractometer [18] and the HB-3A four-circle diffractometer [19] at the High Flux Isotope Reactor at Oak Ridge National Laboratory. For the powder diffraction measurements we employed 1.536 Å and 2.410 Å neutron wavelengths that were produced by (115) and (113) reflections, respectively, from a vertically focusing Ge monochromator.…”