Ultrafast internal dynamics of chiral domain walls probed by time-resolved x-ray resonant magnetic scattering

We measure the picosecond dynamics of labyrinthine stripe domains with chiral Néel-type domain walls using time-resolved x-ray resonant magnetic scattering (XRMS). At the stripe-domain wavevector, the helicity-summed signal shows ultrafast demagnetization and recovery together with a weak oscillatory contribution attributed to laser-launched coherent surface phonons. In contrast, the dichroic signal, which is sensitive to the in-plane magnetization within the Néel domain walls, exhibits a pronounced oscillatory response. Interestingly, the observed frequency of domain wall dynamics decreases with increasing pump fluence. We associate this frequency decrease with a transient softening of the domain-wall restoring potential following optical excitation. This finding highlights that time-resolved XRMS isolates internal domain-wall dynamics and provides reciprocal-space access to wall-specific degrees of freedom in disordered stripe textures on picosecond time scales.