X-Ray Magnetic Dichroism (XMCD) is a differential absorption spectroscopy that exploits the interaction of x-ray circular polarized radiation with magnetic samples. It combines the information of the local sensitivity of core level excitation with the magnetic one. This spectroscopy provides the spin and the orbital magnetic moments of the atoms by means of the application of sum-rules.
In a single particle scenario, a two-step model provides an insight into the physical meaning:
1) electrons excited from core levels by circularly polarized light display an average spin momentum depending on the helicity,
2) spin-polarized electrons probes in a different way the spin-resolved density of states above the Fermi level of the magnetized sample. The difference between the absorption taken at different helicity is related to the difference of the spin up and down branches of the density of empty states projected on the absorbing atoms and hence to the spin momentum of the absorbing atom.
XMCD spectroscopy efficiently probes the magnetic properties in the transition L2,3 metal edges (p → d transition) and the rare-earths M4,5 edges (d → f transition) because of the favorable optical selection rules which select the magnetic band as final state.
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