DNS

With the increased flux and efficiency delivered by the FRM II, DNS becomes ideal for the studies of complex spin correlations, such as in highly frustrated magnets and strongly correlated electrons, as well as of the structures of soft condensed matter systems, such as the nanoscale confined polymers and proteins, via polarisation analysis. The exploration of unusual magnetic properties can also be efficiently undertaken on single-crystal samples by reciprocal space mapping. In addition to the separation of magnetic cross section from nuclear and spin-incoherent ones, polarisation analysis also allows to distinguish in detail the anisotropy of spin correlations. It has also been well demonstrated that polarised powder diffraction on DNS is complementary to standard neutron powder diffraction and may be extremely useful for magnetic structure refinements, particularly in case of small moments by improving the signal to background ratio. DNS also represents a powerful instrument for the soft condensed matter community for the separation of nuclear coherent scattering from often dominating spin incoherent scattering background. The main applications can be summarised:

• Application of polarisation analysis: uniaxial-, longitudinal-, and vector-PA
• Magnetic, lattice, and polaronic correlations: geometrically frustrated magnets, strongly correlated electrons, emergent materials
• Single-crystal and powder time-of-flight spectroscopy: single-particle excitations, magnons and phonons
• Soft condensed matters: separation of coherent scattering from hydrogenous materials, polymer, liquids and glasses

• Top-loading CCR
• Closed-cycle cold head
• Orange-type cryostat
• Cryo-furnace
• Dilution ³He/ ⁴He cryostat insert (~20 mK)
• Cryomagnet (self-shielding, vertical field up to 5 T)

Monochromator

• Neutron guide NL6-S
  • Horizontally and vertically adjustable, double-focusing
• PG(002), d = 3.355 Å
• Crystal dimensions: 2.5 × 2.5 cm² (5 × 7 crystals)
• Wavelength range: 2.4 Å < λ < 6 Å

Neutron velocity selector

• Minimum wavelength: 1.5 Å @ 22000 rpm
• Resolution Δλ/λ: 30 – 40%

Chopper

• Chopper frequency: ≤ 300 Hz
• Repetition rate: ≤ 900 Hz
• Chopper disc: Titanium, 3 slits, Ø = 420 mm

Flux at sample

• Non-polarised: ~ 10⁸ n cm^-2 s^-1
• Polarised: ~ 5·10⁶ – 10⁷ n cm^-2 s^-1
  • (polariser: m = 3 supermirror benders)

Detector banks for non-polarised neutrons

• 128 position sensitive ³He tubes
  • Ø = 1.27 cm, height ~100 cm
• Total solid angle covered: 1.9 sr
• Covered scattering angles in the horizontal plane: 0° < 2θ ≤ 135°

Detector banks for polarised neutrons

• 24 detection units:
  • Polarisation analysis by m = 3 supermirror benders
  • ³He detector tubes, Ø = 2.54 cm, height 15 cm
• Covered scattering angle in the horizontal plane: 0° < 2θ ≤ 150°
• Q_max
  • λi = 2.4 Å (E_i = 14.2 meV): 4.84 Å^-1
  • λi = 6 Å (E_i = 2.28 meV): 1.93 Å^-1

Energy resolution

• λi = 2.4 Å (E_i = 14.2 meV): 1 meV
• λi = 6 Å (E_i = 2.28 meV): 0.1 meV