Paper detail

Nucleation and high-density packing of 360° domain walls on planar ferromagnetic nanowires by using circular magnetic fields

We propose a mechanism for nucleation and high-density packing of 360° domain walls (DWs) on planar ferromagnetic nanowires, of 100 nm width, by using circular magnetic fields. The extent of the stray field from a 360° DW is limited in comparison to 180° DWs, which allows them to be packed more densely than 180° DWs in a potential data storage device. We use micromagnetic simulations to demonstrate high-density packing of 360° DWs, using a series of rectangular 16 x 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 result in the adjacent walls breaking into 180° DWs and annihilating.