Layer resolved magnetization dynamics in coupled ferromagnetic bilayers using time resolved X-ray magnetic circular dichroism

Two ferromagnetic layers antiferromagnetically coupled by interlayer exchange, usually called a synthetic antiferromagnet, evolve to important layer systems for storage applications, e.g. as free layer in toggle-switching magnetic random access memory or as storage medium in hard disk drives. Because of the growing operation speed of such devices, the investigation of the magnetization dynamics in interlayer exchange coupled magnetic bilayers with layer resolution is of interest. Here, interlayer exchange coupled Co90Fe10/Ru/Ni81Fe19 bilayers are investigated using time resolved X-ray magnetic circular dichroism in transmission. By detecting the dichroic signal at the Ni or Co L3 absorption edge with time resolution, the magnetization dynamics of the individual magnetic layers is observed separately. Two different waveguide stack geometries allow for in-phase and anti-phase excitation of both layers using both, pulsed and continuous wave (cw) excitation. Using cw-excitation the layer resolution allows the direct observation of in-phase or anti-phase precession for acoustical and optical mode, respectively. With pulsed excitation we were able to observe a phase shift of the precessional signal due to coupling