Phase and amplitude of element-specific moment precession in Ni81Fe19Ni81Fe19

We present a time and element-resolved measurement of magnetization dynamics during ferromagnetic resonance (FMR) in a single layer of Ni81Fe19Ni81Fe19. Small-angle (<1∘<1∘) precession of elemental Ni, Fe moments could be measured directly and quantitatively using time-resolved X-ray magnetic circular dichroism (XMCD) in transmission. The high temporal and rotational sensitivity of this technique has allowed quantification of the phase and amplitude of driven FMR motion at 2.3 GHz, verifying basic expectations for a driven resonance.