Surface acoustic waves (SAW) and pinning of magnetic domain walls in a ferromagnetic multilayer.

The pinning of magnetic domain walls (DW) results in reduced velocities and non-deterministic motion of domain walls. Perpendicular anisotropy (PMA) materials display narrow, stable DWs but the pinning barriers have a significant effect due to the small width. We investigate the effects of SAW on pinning and motion of domain walls in films of Cr(2nm)/Pt(2nm)/[Co(0.3nm)/Pt(0.6nm)]₅ that are patterned into micron wide stripes between a pair of inter-digital transducers (IDTs), all on a 128 -Y cut LiNbO₃ substrate. Measurements were made using a magneto-optical Kerr effect microscope. Preliminary measurements of DW motion using magnetic field pulses, varying both the width and the height of the pulse identified the location, pinning potential and critical field of highly reproducible strong pinning sites. The effect of SAW on these well characterized pinning sites indicate that SAW are able to depin DW even from deep pinning potentials. The standing wave generated by the IDT pair allows for measurements at both the and antinodes of the SAW. Between these deep pinning sites, DW motion is consistent with creep behavior, with increasing SAW amplitude increasing the DW velocity.