  We study a system of Dirac electrons with finite density of charge carriers
coupled to an external electromagnetic field in two spatial dimensions, with a
domain wall (DW) mass term. The interface between a thin-film ferromagnet and a
three-dimensional topological insulator provides a condensed-matter realization
of this model, when an out-of-plane domain wall magnetization is coupled to the
TI surface states. We show how, for films with very weak intrinsic in-plane
anisotropies, the torque generated by the edge electronic current flowing along
the DW competes with an effective in-plane anisotropy energy, induced by
quantum fluctuations of the chiral electrons bound to the wall, in a mission to
drive the internal angle of the DW from a Bloch configuration towards a N\'eel
configuration. Both the edge current and the induced anisotropy contribute to
stabilize the internal angle, so that for weak intrinsic in-plane anisotropies
DW motion is still possible without suffering from an extremely early Walker
breakdown.
