  In conducting ferromagnetic materials, a moving domain wall induces eddy
currents in the sample which give rise to an effective retarding pressure on
the domain wall. We show here that the pressure is not just proportional to the
instantaneous velocity of the wall, as often assumed in domain wall models, but
depends on the history of the motion. We calculate the retarding pressure by
solving the Maxwell equations for the field generated by the eddy currents, and
show how its effect can be accounted for by associating a negative effective
mass to the magnetic wall. We analyze the dependence of this effect on the
sample geometry and discuss the implications for Barkhausen noise measurements.
