Geometric tailoring of domain wall traps and diodes in ferromagnetic nanostripes
Geometric tailoring of magnetic responses is a central theme in modern magnetism. By employing cross-sectional geometric modulation, we investigate how geometric variations influence the dynamics of field-driven domain walls. This approach enables the realization of a domain-wall trap, achieved through a nanostripe constriction, and a domain-wall diode, realized via a wedge-shaped expansion. We demonstrate that domain walls can be efficiently pinned by cross-sectional modulation, with the depinning field exhibiting strong dependence on the cross-sectional gradient. Under weak applied fields, the domain wall undergoes localized oscillations near the pinning site; under strong fields, this pinning breaks down, reproducing the typical diode characteristics. Theoretical calculations based on a biaxial ferromagnet model and a collective-variable approach are in excellent agreement with micromagnetic simulations. Finally, we delineate the parameter regime for realistic samples in which these predicted effects are most pronounced.