| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | Daniel Higley, SLAC National Accelerator Laboratory |
| Authors: | D.J. Higley, SLAC National Accelerator Laboratory K. Hirsch, SLAC National Accelerator Laboratory E. Yuan, SLAC National Accelerator Laboratory E. Jal, SLAC National Accelerator Laboratory G.L. Dakovski, SLAC National Accelerator Laboratory A.A. Lutman, SLAC National Accelerator Laboratory J. MacArthur, SLAC National Accelerator Laboratory A.H. Reid, SLAC National Accelerator Laboratory T. Liu, SLAC National Accelerator Laboratory J. Joseph, Lawrence Berkeley National Laboratory A. Tsukamoto, Nihon University H.A. Durr, SLAC National Accelerator Laboratory W.F. Schlotter, SLAC National Accelerator Laboratory |
| Correspondent: | Click to Email |
In the last twenty years, the field of ultrafast magnetization dynamics has seen tremendous growth and development. Ferromagnetic transition metals have been seen to demagnetize on a sub-picosecond time-scale when excited by ultrafast laser pulses, much faster than expected from dynamics close to equilibrium. The mechanism of this ultrafast magnetization quenching, almost twenty years after its discovery, is still a matter of active debate. Other materials exhibit ultrafast switching of the magnetization when excited similarly. The switching mechanism, however, is also still debated. To unravel the mysteries of these processes requires probes which can sensitively and reliably probe the transfer of angular momentum and energy between the electronic, electronic spin, and lattice systems.
X-ray magnetic circular dichroism spectroscopy (XMCD) directly and element-specifically probes the spin and orbital magnetic moments of electrons in matter and has proven invaluable in studies of static magnetism. This information is extracted from the difference in absorption of right- and left-circularly polarized x-rays at spin-orbit split resonances where core-level electrons are excited into unoccupied valence states.
XMCD with femtosecond time resolution is an ideal tool to investigate ultrafast magnetization dynamics. Femtoslicing beamlines at synchrotrons have been used to perform such measurements and make seminal contributions to the field of ultrafast magnetization dynamics. The low photon throughput of these sources, however, necessitates long integration times for measurements and restricts the possibility of systematic studies as well as measurement of small signals. X-Ray Free Electron Lasers (XFELs), which provide femtosecond pulses with a much increased flux compared to femtoslicing sources, give an important path to extending these results.
Here, we report on ultrafast XMCD spectroscopy measurements in the soft x-ray range at an XFEL utilizing a recently installed variable polarization undulator at the XFEL LCLS at the SLAC National Accelerator Laboratory. We are able to record static XMCD spectra of GdFeCo samples over the iron L-edges and gadolinium M5 edge which match those observed at synchrotrons. In addition, by monitoring the time-resolved XMCD at these edges we reproduce the classic observation of a transient ferromagnetic alignment of antiferromagnetically coupled spins in amorphous GdFeCo during ultrafast, laser-induced, switching. With the high-flux and intrinsically ultrafast pulses of XFELs, we are able to record this measurement in less than an hour, a fraction of the time required for the original measurement.