Domain Wall Depinning in the Presence of Multiple Paths and Multiple Pinning Sites

The stochastic behavior of magnetic domain walls (DW) may be an impediment to their use in racetrack memories. Here, we investigate the path of DWs in Co/Pt multilayers with perpendicular anisotropy, after depinning from photolithographically patterned notches that act as strong pinning sites. We focus on the effects of strain in the form of surface acoustic waves with a frequency of 244.75 MHz. Measurements were performed using a scanning MOKE stage focused on the notches. This allowed for measurements of the domain wall transit time after depinning over a range of strain values. The corresponding probabilities indicate that the DWs could traverse a variety of paths, each of which consisted of multiple pinning sites. Strain altered the pinning landscape, with increasing strain resulting in shorter characteristic depinning time for all paths. Hence, paths with short depinning times, showed little to no discernible pinning as strain increased, whereas paths with very long characteristic times (and thus, small probabilities) instead became more visible at higher strain.