Observation of asymmetrical pinning of domain walls in notched Permalloy nanowires using electron holography

Field-driven domain-wall motion and pinning in notched Permalloy nanowires have been observed using electron holography and Lorentz microscopy. Transverse domain walls (TDWs) were identified and different aspects of their behavior, including nucleation, injection, pinning, and depinning, were studied. The relative chirality (i.e., sense of field rotation) of the notch and the nucleation pad had a major influence in determining the TDW propagation: the walls were preferentially pinned for a notch of opposite chirality, but simply passed through when the notch had the same chirality. This asymmetrical TDW pinning accounts for the observed asymmetrical hysteresis hoop.