Excitation of magnetic materials by powerful femtosecond laser pulses leads to magnetization dynamics on the timescale of exchange interactions. The emerging dynamics can be probed using conventional magneto-optical methods when the ferromagnet is composed of only one magnetic element [1].
Many ferromagnets, such as permalloy (Py) or yttrium iron garnets (YIG), can exhibit rather complex magnetic structures and are composed of more than one element. For those cases, X-ray circular magnetic dichroism (XMCD) measurements allow to access the individual dynamics of the different elements in the alloy.