Layer resolved magnetization dynamics in coupled magnetic films using time-resolved x-ray magnetic circular dichroism with continuous wave excitation

Time-resolved x-ray magnetic circular dichroism was used to investigate ferromagnetically coupled CoFe/Ru/NiFe bilayers. The magnetization dynamics was driven by a continuous wave excitation. The precessional motion of the individual layers was detected separately by tuning the x-ray photon energy to the L3 absorption edge of either Ni or Co. Using two different waveguide stack geometries in-phase and antiphase excitation could be selected showing its effect in the measured precessional signal of the individual layers. In exchange-coupled bilayer two precessional modes were observed for each layer. The relative phase angles of the magnetic response between the two layers were found to be 8° and 133°, for the two modes revealed their quasiacoustic and quasioptic character.