  Ultrafast optical pumping of spatially nonuniform magnetic textures is known
to induce far-from-equilibrium spin transport effects. Here, we use ultrafast
x-ray diffraction with unprecedented dynamic range to study the laser-induced
dynamics of labyrinth domain networks in ferromagnetic CoFe/Ni multilayers. We
detected azimuthally isotropic, odd order, magnetic diffraction rings up to 5th
order. The amplitudes of all three diffraction rings quench to different
degrees within 1.6 ps. In addition, all three of the detected diffraction rings
both broaden by 15% and radially contract by 6% during the quench process. We
are able to rigorously quantify a 31% ultrafast broadening of the domain walls
via Fourier analysis of the order-dependent quenching of the three detected
diffraction rings. The broadening of the diffraction rings is interpreted as a
reduction in the domain coherence length, but the shift in the ring radius,
while unambiguous in its occurrence, remains unexplained. In particular, we
demonstrate that a radial shift explained by domain wall broadening can be
ruled out. With the unprecedented dynamic range of our data, our results
provide convincing evidence that labyrinth domain structures are spatially
perturbed at ultrafast speeds under far-from-equilibrium conditions, albeit the
mechanism inducing the perturbations remains yet to be clarified.
