DOMAIN WALL MOTION IN MAGNETIC NANOTUBES INDUCED WITH TIME-DEPENDENT FIELDS
The dynamics of vortex domain walls (VDWs) in ferromagnetic nanotubes induced with dc and ac magnetic fields is investigated theoretically. Such domain walls (DWs) are physical objects living in a fairly rich energy landscape with paths that can be tailored. In this way, two different Walker fields has been already predicted to appear in the tubes, a fact that was attributed to the breaking of left-right symmetry of the walls. The physical origin of such behavior is the interplay between the curvature of the ferromagnetic nanomembrane and the dipole field of the VDW. In this paper it is predicted that the excitation of such domain walls with time-dependent fields may be useful in a variety of situations. First, to avoid the Walker breakdown (and to increase the average velocity) a time-dependent field can be superimposed to a dc field, allowing to control the wall by trapping it in a potential well. This is achieved with a proper combination of dc and ac fields needed to avoid the wall to overcome the energy barriers associated to the Walker breakdown fields, frustrating then the precessional DW motion and increasing the average DW speed. The wall is further pumped with the time-dependent field in a breathing mode, near the top of the energy barrier. This pumping mechanism may be also useful for the generation of spin waves.