We report a new method for studying magnetism at the atomic level with site selectivity. It is based on thecombination of the site-selective diffraction-based x-ray standing wave (XSW) technique and x-ray magneticcircular dichroism (XMCD), which provides the magnetic sensitivity. The use of the standing wave resultingfrom an interference between the incoming and the Bragg reflected electromagnetic waves ensures that the phaseinformation is not lost and thus brings information about the magnetism at a given site directly. In the paper, weprovide the theoretical foundations of such a method based on the dynamical theory of x-ray diffraction andtime-dependent perturbation theory. By means of computer simulations, the principle of the method is thuspresented in a rather accessible way. Finally, we demonstrate the results of a proof-of-principle experiment onsingle-crystalline yttrium-iron-garnet (YIG, Y₃Fe₅O₁₂). We show data exhibiting a clear variation in the XMCDsignal caused by the standing wave. A comparison with theoretical functions illustrates that the established theoryreliably describes the phenomena involved and allows to extract useful information about the magnetic momentsin YIG.
Kaminski et al. (Thu,) studied this question.