Domain wall depinning from geometric notches using surface acoustic waves

The ability to move and pin magnetic domain walls (DWs) requires an understanding of the energy landscapes that pin them and the external forces that drive them. The technological implications of the ability to reproducibly and reliably drive DWs are significant. Magnetic fields, operating in the flow regime, can and do succeed at depinning but are energetically expensive and difficult to focus. Here, we use high frequency strain in the form of surface acoustic waves to substantially alter the depinning probability of magnetic DWs that are pinned at lithographically patterned notches in thin films of Co/Pt heterostructures. Strain alters the pinning energies in a distinctly different manner than magnetic fields, altering only the energy contained in a DW and not the Zeeman energy. The interplay and efficiency of strain-assisted and magnetic field driven depinning depend sensitively on the details of the patterned pinning sites. Our data show that the presence of strain waves can result in a 100% probability of depinning even at low magnetic fields. This, together with the ability to focus and/or pattern the strain wave amplitudes via careful design, makes for a novel and technologically feasible method of controlling DW motion.