Geometry dependence of magnetization vortices in patterned submicron NiFe elements

When the magnetization is switched in patterned submicron ${\mathrm{Ni}}_{\mathrm{80}}{\mathrm{Fe}}_{\mathrm{20}}$ thin-film elements, magnetization vortices, local micromagnetic structures with a core size of 10 nm, are often trapped. This lowers the magnetostatic self-energy of the elements. Trapped vortices can cause anomalous switching during spin reversal between stable magnetization states. To expel trapped vortices, a large external magnetic field, the vortex exit field, is required. The dependence of the vortex exit field on lateral dimensions of the patterned elements is measured. In the limit where the lateral dimensions of the patterned elements are much larger than the vortex core size, smaller structures are more prone to the formation of trapped vortices.