Abrupt increase of stochastic behavior in domain-wall motion near depinning field

Abstract

The domain-wall motion in ferromagnetic films exhibits stochastic behavior due to thermal agitation with quenched disorders. The stochasticity is an obstacle in the sense of consistent repeatability of domain-wall position control in magnetic domain-wall devices. In general, the level of stochasticity is expected to decrease as driving force increases. This property suggests that the magnetic domain-wall devices are capable of simultaneously achieving both high operational speed and decrease in the level of stochasticity. However, we report here an observation of stochasticity anomaly, which involves a significant increase in relative speed dispersion near the depinning field. Domain-wall motion measurements were performed in ferromagnetic wires with perpendicular magnetic anisotropy over the same position to measure the relative speed dispersion. The stochasticity in domain-wall motion is intertwined with the number of pinning-depinning events throughout the domain-wall motion. The size of cluster events, which leads to the number of events, reflects the trend in the relative speed dispersion. The observed anomaly is provided by occurrence of large avalanches of cluster events. The anomaly occurs within the tech-relevant speed range of 1-100 m/s, signaling the necessity of material engineering to mitigate its effects.