Simulated experiment

Neutrons from the reactor are moderated in the graphite hot source so that the maximum flux is at a short wavelength.

• Hot neutrons enter beam tube H4 and go to the polarising monochromator which diffracts only neutrons with a given wavelength and spin polarisation.
• The guide-field maintains the polarisation state of this beam.
• The cryoflipper reverses alternately the polarisation state of the beam.
• The sample - a ferromagnetic or paramagnetic single crystal - is in a magnetic field and is cooled down or warmed up in a cryostat.
• For each Bragg reflection, the peak intensity depends on each polarisation state of the beam. A Fourier component of the magnetisation distribution in the crystal is obtained from the two intensities.

• The sample is lowered through the variable temperature insert of the cryomagnet into the beam.
• It is rotated so that a given set of crystal planes diffracts the beam.
• The detector is rotated and lifted towards the diffracted beam.
• The magnetisation distribution shown in the corner is derived from the ratio of the intensities measured with the two polarisations.