Depinning Field at Notches of Ferromagnetic Nanowires With Perpendicular Magnetic Anisotropy

In this paper, we experimentally characterize the domain-wall depinning mechanism at notches of ferromagnetic nanowires with perpendicular magnetic anisotropy. A time-resolved magneto-optical Kerr effect detection reveals that the depinning time is exponentially proportional to the strength of external magnetic field. From an analysis based on Neacuteel-Brown theory, the depinning field and the activation volume are quantitatively determined for several notches with different gap distances. Interestingly, both the depinning field and the activation volume are proportional to the inverse of the gap distance. This is explained by the sizeable extrinsic effect from geometric constrictions in contrast to the intrinsic properties of the films.