Measurement of domain wall dynamics in response to ultrafast optical pumping by use of coherent X-ray scattering at the Linac Coherent Light Source*

We used coherent X-ray resonant magnetic scattering at the Linac Coherent Light Source to study the dynamic response of a nanoscale magnetic domain network in a [Co90Fe10/Ni] multilayer after ultrafast optical pumping. The signal to noise was sufficient for us to observe both the first and third order magnetic diffraction rings produced by the domain network, allowing us to interrogate how ultrafast optical pumping affects details of the domain wall structure. We found that the first and third order diffraction rings exhibit different dynamics. Our results suggest that the magnetization dynamics of magnetic features depends on their size, and that the ultrafast dynamics of the domains and domain walls are different when subject to ultrafast optical pumping. We will present an analysis of the data in terms of ultrafast generation of spin currents that flow between the domains.