Surface Acoustic Waves and Magnetic Domain Wall Motion

The interest in domain wall based memories in materials with perpendicular magnetic anisotropy has motivated our study into how strain affects domain wall pinning. Specifically, we have investigated the effects of high frequency strain on domain wall motion in ferromagnetic stripes. A pair of interdigital transducers were lithographically patterned on 128° Y cut LiNbO₃, resulting in surface acoustic waves (SAW) at a resonance frequency of 244.75 MHz. Stripes with widths ranging from 2 to 5 μm of Co/Pt multilayers were patterned between the two IDTs, with notches at 8 um intervals serving as geometrically defined pinning sites. We characterized the pinning behavior of the notches using a scanning MOKE stage, for a range of magnetic fields and pulse widths, both with and without strain. The latter data allowed for us to extract the pinning potential and depinning field for each notch. Measurements of the depinning probabilities over a range of SAW amplitudes indicate that as the SAW amplitude increases, the characteristic depinning time decreases monotonically showing that strain assists in domain wall depinning by lowering the energy required.