Nucleation and interactions of 360∘ domain walls on planar ferromagnetic nanowires using circular magnetic fields

We propose a mechanism for nucleation of 360∘ domain walls (DWs) on planar ferromagnetic nanowires, of 100 nm width, by using circular magnetic fields, and find the minimal spacing possible between 360∘ DWs. The extent of the stray field from a 360∘ DW is limited in comparison to 180∘ DWs, allowing 360∘ DWs to be spaced more closely without interactions than 180∘ DWs, which is potentially useful for data storage devices. We use micromagnetic simulations to demonstrate the positioning of 360∘ DWs, using a series of rectangular 16 × 16 nm2 notches to act as local pinning sites on the nanowires. For these notches, the minimum spacing between the DWs is 240 nm, corresponding to a 360∘ DW packing density of 4 DWs per micron. Understanding the topological properties of the 360∘ DWs allows us to understand their formation and annihilation in the proposed geometry. Adjacent 360∘ DWs have opposite circulation, and closer spacing results in the adjacent walls breaking into 180∘ DWs and annihilating.