  We find that dipolar interactions favor ferromagnetic ordering of elongated
crystals of Mn12 Acetate below 0.8 K. Ordered crystals must possess domain
walls. Motion of the wall corresponds to a moving front of Landau-Zener
transitions between quantum spin levels. Structure and mobility of the wall are
computed. The effect is robust with respect to inhomogeneous broadening and
decoherence.
