N, M in quad. - Pi // Oy
The incident polarisation vector is chosen parallel to the Y axis, i.e. perpendicular to the scattering vector Q. The direction of the scattered polarisation is shown in red.
When N and M (in green) are in quadrature, the polarisation rotates around the magnetic interaction vector M, i.e. no rotation in the example shown. The angle of rotation, when Pi is not parallel to M, depends on the ratio of the amplitudes of N and M (e.g. π/2 when M=N). We can see that the cross-section does not necessarily depend on the relative amplitudes of the nuclear and magnetic structure factors.