  The geometry and morphology of magnetic domain walls (DWs) are closely
related to their dynamics when driven by external forces. Under some reliable
approximations DWs can be considered self-affine interfaces, so universal laws
govern their behavior. On the other hand, large-scale DW structure has been
less explored so far. Recently, it has been shown that bubble-like magnetic
domains can be strongly deformed on a large scale by applying alternating (ac)
magnetic field pulses. In the present work, we conduct a comprehensive analysis
of DW structure at both small and large length scales in bubble-like domains
present in ferromagnetic thin films with perpendicular anisotropy, focusing on
its initial evolution under the application of ac magnetic pulses. Results
obtained from the widely used roughness correlation function B(r) and its
corresponding structure factor, are consistent with those obtained from the
spatial autocorrelation function of DW fluctuations. Whereas the roughness
exponent slightly increases during the ac evolution, a strong deformation is
observed at a large scale, where a striking periodicity (statistically
speaking) is observed. This period is probably determined by the boundary
conditions and a characteristic intrinsic length.
