Vortex Domain Wall Formation in Permalloy Nanowires with Geometric Pinning Sites

An optimal geometric pinning site on Permalloy nanowires of varying widths has been investigated and applied in a magnetic memory scenario using micromagnetic simulations. Minimal limits on two key factors; the applied field length and the domain wall formation length are established such that vortex domain walls are reliably formed in the structures to facilitate lower powered domain wall movement using spin-polarised current. The symmetric wires with the nanoconstrictions at both sides have been found to favour the formation of the vortex domain wall compared with the asymmetric wires with the nanoconstrictions at only one side of the wires. The detailed micromagnetic simulations show that the domain wall formation length and the applied field length are optimal to form the vortex domain walls when they are equal to the nanowire width.