Novel Method for Reducing Operation Current in Magnetic Domain-Wall Motion by the Use of Curved Wedge Nanowire

We propose a method to reduce the operation current of domain-wall (DW) motion in ferromagnetic nanowires with perpendicular magnetic anisotropy. It is based on the phenomena that a DW placed in wedged nanowire geometry moves spontaneously without any external magnetic field by consumption of the DW energy. Based on energy consideration, we found that there exists a geometry-induced effective field, which depends solely on the radius of circular arc intersecting normal to both the nanowire edges. Geometry for a constant effective field is analytically given with a curved wedge shape, which keeps the radius unchanged irrespective of the DW position. The validity of the analytic prediction is confirmed by a micromagnetic simulation.