  Recent experimental studies of magnetic domain expansion under easy-axis
drive fields in materials with a perpendicular magnetic anisotropy have shown
that the domain wall velocity is asymmetric as a function of an external in
plane magnetic field. This is understood as a consequence of the inversion
asymmetry of the system, yielding a finite chiral Dzyaloshinskii-Moriya
interaction. Numerous attempts have been made to explain these observations
using creep theory, but, in doing so, these have not included all contributions
to the domain wall energy or have introduced additional free parameters. In
this article we present a theory for creep motion of chiral domain walls in the
creep regime that includes the most important contributions to the domain-wall
energy and does not introduce new free parameters beyond the usual parameters
that are included in the micromagnetic energy. Furthermore, we present
experimental measurements of domain wall velocities as a function of in-plane
field that are well decribed by our model, and from which material properties
such as the strength of the Dzyaloshinskii-Moriya interaction and the
demagnetization field are extracted.
