Surface acoustic waves assisted domain wall depinning from patterned notches in micron sized wires.

Surface acoustic waves (SAW) create high frequency strain fields that interact with ferromagnetic (FM) thin films via the magneto-strictive coefficients. SAW decrease the coercive field, change magnetization direction, boost domain wall (DW) velocities, drive precessional switching and substantially increase the depinning probability of DW from randomly distributed pinning sites. Here, we investigate SAW induced depinning of DWs in periodic notches, positioned at nodes and antinodes of the SAW, in a [Co(0.4nm)/Pt(0.6nm)]₅ multilayer using both magneto-optical Kerr effect (MOKE) microscopy and scanning MOKE. These notches act as pinning potential barriers for the DW motion. Characterizing the individual pinning parameters of each notch, specifically the energy barrier (E₀) and intrinsic critical field (H₀), we then turn to the effect of high frequency SAW on these well characterized pinning sites. We find the depinning probability doubles at SAW excitations of 2.5V (corresponding to a strain amplitude of ~1.4×10^-4) in most of the pinning sites and a 4-10 fold increase at 4V excitation. We model this behavior by taking into account the SAW induced changes in the anisotropy and the SAW induced effective magnetic field.