Scattering from a helix

It is clear from eq. (13) that for non-resonant magnetic scattering the different polarization states of the scattered beam contains information on the spin- and orbital-magnetization densities. To develop this further, and to derive useful expressions that may allow us to separate these components experimentally, requires a description of the polarization characteristics of the incident and scattered beams. The detailed analysis required to do this has been developed elsewhere (see, for example, Blume and Gibbs (1988) and references therein), and here we make use of only those steps that are needed for our example of the scattering from a helix. 

In the limit P —> 1, the a-polarized component of the magnetic scattering from a helix depends only on the spin magnetization density, I oc while the r-polarized component depends on the sum of the orbital and spin densities I oc (i + sY- Thus, it is in this sense that the spin and orbital contributions to the total moment may be separated. Semi-quantitative experiments to demonstrate these ideas in a helix have been performed on Ho (Gibbs et al. 1988, Gibbs et al. 1991). Both jt- and a-polarized scattered beams were observed. It was demonstrated that the nr-component is dominant, consistent with the large orbital moment in Ho, and that the Q dependence of the orbital and spin form... 

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