Steering of magnetic domain walls by single ultrashort laser pulses

We present a magnetic domain-imaging study by x-ray magnetic circular dichroism photoelectron emission microscopy on a $\mathrm{Co}/{\mathrm{Fe}}_{75}{\mathrm{Gd}}_{25}$ bilayer under exposure to single focused ultrashort (100 fs) infrared laser pulses. Magnetic domain walls experience a force in the intensity gradient of the laser pulses away from the center of the pulse, which can be used to steer domain walls to move in a certain direction. Maximum domain-wall displacements after individual laser pulses close to $1\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ in zero external field are observed. Quantitative estimates show that electronic spin currents from the spin-dependent Seebeck effect are not strong enough to explain the effect, which we thus attribute to the torque exerted by magnons from the spin Seebeck effect that are reflected at the domain wall.