Domain walls in ring-shaped nanowires under rotating applied fields

摘要

We present a study of the motion of domain walls confined to 1D propagating energy minima in ferromagnetic nanowires. The energy minima are defined by the combination of the geometry of a ring-shaped planar nanowire and the influence of an external magnetic field, and may be controllably propagated via rotation of this field. Focused magneto-optic Kerr effect measurements are used to characterize the walls' behavior at a range of field amplitudes and frequencies. Combining these measurements with simple models allows us to demonstrate that the domain walls propagate by thermally assisted "hopping" between defect sites and that the relative smoothness of their motion can be controlled by variation of the applied field strength. Frequency-domain analysis indicates that the nanowires retain domain wall structure, rather than form quasi-saturated states, over a large range of applied magnetic fields and including fields that result in smooth wall motion. Our results are important to applications where tight control of domain wall position takes precedent over speed, for example, where domain walls are used to trap and transport magnetized particles.