Curvature-driven ac-assisted creep dynamics of magnetic domain walls

The dynamics of micrometer-sized magnetic domains in ultrathin ferromagnetic films is so dramatically slowed down by quenched disorder that the spontaneous elastic tension collapse becomes unobservable at ambient temperature. By magneto-optical imaging we show a weak zero-bias ac field can assist such curvature-driven collapse, making area bubble to reduce measurable rate, spite negligible effect same curvature has on average creep motion driven comparable dc field. An analytical model explains this phenomenon quantitatively.