VErsatile Intense Triple-Axis Spectrometer

VERITAS |  HB-1A | HFIR

HB-1A Triple-Axis Spectrometer

Mission Statement

Diffraction studies of structural and magnetic phase transitions or parametric studies of low-lying magnetic excitations in novel materials.

Instrument Description

The VERITAS triple-axis spectrometer (HB-1A) at the High Flux Isotope Reactor operates at a fixed incident energy of Ei = 14.5 meV (wavelength λ = 2.37 Å) by employing a double-bounce pyrolytic graphite monochromator system. The first monochromator is flat, while the second monochromator is fixed vertically focused. A highly-oriented pyrolytic graphite filter is placed after each monochromator to reduce λ/2 contamination (~0.01%). This configuration gives VERITAS an intense, clean monochromatic beam nearly free of higher-order contamination neutrons. The double-bounce monochromator system, combined with an analyzer for energy discrimination, ensures that the instrument has a low background and an excellent signal-to-noise ratio. The instrument also utilities a four-circle goniometer option which allows data collection in extended reciprocal space for investigating magnetic orders and determining magnetic structures. The instrument is well-suited for investigating the magntic properties of quantum materials, and particularly useful in probing weak scattering signals from single crystals, powders and thin films, covering a wide variety of sample environments, including high-temperature furnaces (≤ 1500°C), ultra-low temperature cryostats (≥ 0.03K), vertical field cryomagnets (≤ 6T), pressure cells (≤ 2GPa), electric field sticks (≤ 10kV), and uniaxial pressure stick (force up to 300 lbs).

Applications

VERITAS serves the condensed matter and materials science communities. The instrument is primarily used for diffraction study of the magnetic properties of bulk/thin film materials, including the following:

  • Quantum materials
  • High-Tc superconducting materials
  • Frustrated magnets
  • Multifunctional materials
  • Topological materials

VERITAS is also optimized for parametric study of low-lying magnetic excitations (up to ~ 9 meV). 

Specifications

Beam Spectrum Thermal
Monochromator PG(002), double-bounce monochromator system
  M1 is flat, M2 is fixed vertically focused
Monochromator angle 2Θ M = 41.3° Ei ≈ 14.5 meV
Analyzers PG(002), fixed vertically focused
Sample angles

±180°
Scattering angle -5 to 130°
Analyzer angles -60° < 2ΘA < 120°
Detector Single 3He gas counter
Collimations Premonochromator: 40′
Monochromator-sample: 20′, 40′
Sample-analyzer: 20′, 40′ 
Analyzer-detector: 20′, 80′
Filters Sapphire pre-monochromator
2 pyrolytic graphite filters each mounted after
M1 and M2, respectively (λ/2 ≈ 10-4 λ)
Flux at sample ~4.2 × 107 n/cm2/s
Momentum range 0.2 to 4.8 Å-1 (elastic configuration)