D3 - The Spin Polarised Hot Neutron Beam Facility
Reactor hall, hot neutron beam H4
Hot Source at 2000°C
7° < 2θM < 38°
0.42 Å < λ < 0.843 Å
polarising, high-flux, low resolution
Heusler Cu2MnAl (111)
polarising, less-flux, better resolution
non-polarised, high flux, high resolution
40mK < T < 300K
3He spin analyser
Neutron polarisation ≈ 70%-85%
0.01T < H < 0.6T
1.5K < T < 300K
-24° < ν < +5°
1.0T < H < 9.8T
1.5K < T < 750K
-24° < ν < +5°
Maximum sample size
Diameter: 12 mm
Height: 12 mm
The diffractometer uses readily exchangeable CoFe and Heusler polarising monochromators within removable shielded cassettes in symmetric Laue geometry. Wavelength change is an automatic on-line operation, including the insertion of the appropriate resonant harmonic filter. This is particularly useful when extinction or multiple scattering are present. The beam polarisation rate depends slightly on the inpile collimation (channel A or B), the monochromator and the wavelength used.
For mesurements carried out with an applied magnetic field, polarisation reversal is made with a cryoflipper for which the efficiency is wavelength and field independent. A pneumatic half-shutter system in front of the 5cm diameter single 3He detector facilitates the determination of the exact orientation matrix for the crystal. A layout of D3 with the 10 Tesla cryomagnet is presented here.
For polarimetric scattering measurements carried out with Cryopad, the scattered polarisation is analysed with a 3He neutron spin filter hosted by Decpol. Decpol is a compact detector shielding providing the homogeneous holding-field required for long relaxation time of the 3He polarisation.
Several options are available:
- Zero-field neutron polarimetry measurements with Cryopad: antiferromagnetic structures, form factors, etc. Polarisation analysis is made with a 3He neutron spin filter.
- Low-field measurements with the electromagnet: para-, ferro-and some antiferro-magnetic form factors, magnetisation distributions,etc.
- Mid-field/Low temperature measurements with a 2.5 Tesla cryomagnet hosting an ILL dilution insert: para-, ferro- and some antiferro-magnetic form factors, magnetisation distributions,etc.
- High-field measurements with the 10 Tesla cryomagnet: para-, ferro- and some antiferro-magnetic form factors, magnetisation distributions,etc.
Data can readily be analysed on the ILL computing system by a system of programs making use of the Cambridge Crystallography Subroutine Library (CCSL). These provide quick reduction, sorting and averaging of the various data sets already collected. Resulting magnetic struture factors are then Fourier-transformed for direct visualisation of the atomic magnetisation density maps (Maximum Entropy using MemSys code available), and then used to refine physical models for the magnetic electrons.