Domain-Wall Pinning and Depinning at Soft Spots in Magnetic Nanowires

The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni₈₀Fe₂₀ nanowires is used to cause a local reduction of the saturation magnetization Ms and thus a decrease of the energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.