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ILL7 building, Cold neutron guide H15
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(Vertical cold source)
| Key Parameters
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Wavelength
λ [Å] | Takeoff angle
2θ [°] | Polarized Flux
Φ [n cm2 s-1] | Incident Energy
Ei [meV] | δE/E | Qmin/Qmax [Å-1] | 3.12 | 55.1 | 1.2 × 106 | 8.97 | - | 0.14/3.91 | 4.855 | 92.3 | 1.8 × 106 | 3.47 | 4 - 5 % | 0.09/2.5 | Maximum beam size at sample: 55 × 25 mm
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Technical Specifications
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Monochromator | Double focusing HOPG (002), 3 × 5 crystals (7.5 x 1.7 cm2) | Polarizer | Focusing bender supermirror (m=2.8) | Flipper | Adiabatic spin rotation filter (Mezei-type) | Chopper | Cd-coated Al Fermi chopper
Only available for uniaxial polarisation analysis | XYZ Coils | Cu single coil (X, Y), double coil (Z) | Analysers | 66 Schärpf-type bender supermirrors (m=2.8) | Detectors | 3 Banks × 44 detectors (Ø:25 mm (1°), Height: 255mm)
Total angular range: ± 4° < 2θ < ± 145° |
Sample Environment |
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Dedicated
| Orange cryostat: 1.2 - 300 K | Furnace: 300 - 800 K | Pool
| Cryomagnet: up to 5.5 T at sample position | Cryofurnace: 2 - 550 K | Dilution refrigerator: 0.05 - 1.3 K |
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UNDER CONSTRUCTION
Diffuse scattering, found beneath nuclear and magnetic Bragg peaks in a neutron diffraction pattern, yields detailed information on magnetic configurational disorder, and of the interplay between such disorder and local atomic defect structures. However, magnetic disorder scattering is generally small in amplitude and often coexists with nuclear disorder scattering and spin-incoherent scattering. In order to separate each of these components it is necessary to use polarized neutron techniques. D7 features a unique combination of 3-directional (XYZ) polarization analysis in a multidetector setup with the option of time-of-flight energy analysis, in order to examine this diffuse scattering.
A vertically and horizontally focusing pyrolytic graphite monochromator situated in the cold neutron guide H15, monochromates the neutrons with wavelengths of 3.1 Å or 4.8 Å. The beam is polarized using a focusing, m = 2.8 Schärpf bender-type supermirror polarizer. The neutron spins are manipulated using a Mezei-type π-flipper, followed by a set of orthogonal XYZ field coils situated around the sample position. There are currently 66 Schärpf bender-type, m = 2.8 supermirror analysers in the secondary spectrometer in front of 132 3He detectors, situated at 1.5 m from the sample position.
There are two modes of operation of D7:
XYZ Polarization analysis: used for separation of magnetic scattering in disordered/antiferromagnetic samples.
Uniaxial Polarization analysis: used for separation of coherent and spin-incoherent scattering in non-magnetic samples, or the separation of aligned and transverse spins in non-collinear ferromagnets.
The latter can be performed as a time-of-flight inelastic measurement with the addition of a Fermi chopper.
References:
O. Schärpf and H. Capellmann, Phys. Stat. Sol. A 135, 359 (1993)
The XYZ-difference method with polarized neutrons and the separation of coherent, spin incoherent, and magnetic scattering cross sections in a multidetector.
J. R. Stewart, et. al. J. Appl. Phys. 87, 5425, (2000)
Magnetic diffuse scattering in disordered systems studied by neutron polarization analysis
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