  Using a time-resolved detection scheme in scanning transmission X-ray
microscopy (STXM) we measured element resolved ferromagnetic resonance (FMR) at
microwave frequencies up to 10\,GHz and a spatial resolution down to 20\,nm at
two different synchrotrons. We present different methods to separate the
contribution of the background from the dynamic magnetic contrast based on the
X-ray magnetic circular dichroism (XMCD) effect. The relative phase between the
GHz microwave excitation and the X-ray pulses generated by the synchrotron, as
well as the opening angle of the precession at FMR can be quantified. A
detailed analysis for homogeneous and inhomogeneous magnetic excitations
demonstrates that the dynamic contrast indeed behaves as the usual XMCD effect.
The dynamic magnetic contrast in time-resolved STXM has the potential be a
powerful tool to study the linear and non-linear magnetic excitations in
magnetic micro- and nano-structures with unique spatial-temporal resolution in
combination with element selectivity.
