Polarisation optimisation for ferromagnetic diffraction: A case study of iron

The magnetic effect from a ferromagnet can be measured in a non-resonant X-ray diffraction experiment by controlling the polarisation of the incident beam with a phase retarder. However, the results strongly depend on the parasitic polarisation caused by fluctuations of the orbit. We found that by inserting a Si (333) channel-cut polariser with a Bragg angle close to 45 degrees in front of the diamond phase-plate, most of the unwanted polarisation was rejected and the magnetic effect was enhanced. We demonstrate the performance of this experimental configuration for non-resonant ferromagnetic diffraction with the example of iron. The ratio of magnetic to charge scattering from ferromagnetic iron was increased up to three times for the (220) reflection of Fe by combining the channel-cut crystal and the phase-plate. Also, by setting the psi angle of the phase retarder to 11 degrees rather than 45 degrees, the measurements of the magnetic effect were less affected by the presence of multiple reflections occurring in the diamond phase-plate. (c) 2006 Elsevier B.V. All rights reserved.