Zero-field skyrmion creation via surface acoustic waves

We investigate the effect of high-frequency surface acoustic waves on skyrmion bubbles in Cr/Ta/Pt/CoFeB/Pt heterostructures on 128° Y cut lithium niobate. The as-deposited samples are in a single-domain state. Low-temperature annealing yields a multi-domain state, and a subsequent field sweep results in the nucleation of bubbles with significantly increased density in the presence of propagating or standing surface acoustic waves. This increase stems from the strain-driven modifications to the magnetic anisotropy that lowers the barriers to nucleation in pinning sites near the nucleation threshold.