Sub-15-fs X-ray pump and X-ray probe experiment for the study of ultrafast magnetization dynamics in ferromagnetic alloys

Abstract

In this paper, we present a new setup for the measurement of element-specific ultrafast magnetization dynamics in ferromagnetic thin films with a sub-15-fs time resolution. Our experiment relies on a split and delay approach which allows us to fully exploit the shortest X-rays pulses delivered by X-ray Free Electrons Lasers (close to the attosecond range), in an X-ray pump – X-ray probe geometry. The setup performance is demonstrated by measuring the ultrafast elemental response of Ni and Fe during demagnetization of ferromagnetic Ni and Ni80Fe20 (Permalloy) samples upon resonant excitation at the corresponding absorption edges. The transient demagnetization process is measured in both reflection and transmission geometry using, respectively, the transverse magneto-optical Kerr effect (T-MOKE) and the Faraday effect as probing mechanisms.

Symmetry-dependent ultrafast manipulation of nanoscale magnetic domains

“…For the anisotropic scattering, we observed a larger quench of the demagnetization with increase in pump fluence. These results are in agreement with previous works [14,16,17,[27][28][29] and validates the 2D fitting approach.…”

All-optical switching on the nanometer scale excited and probed with femtosecond extreme ultraviolet pulses

“…On the other hand, the observed quantitative agreement between micro-and nanoscale gratings, suggests that we have not yet reached the fundamental spatial limits for AOS. Secondly, while high intensity XUV photon-matter-interaction is a novel and not well explored area of research, it is generally assumed that electron-electron scattering very rapidly thermalizes the initially strongly non-equilibrium electron distributions, leading to comparable demagnetization and AOS processes as observed in the optical regime 36,37 . Finally, we would like to point out that significantly smaller optically reversed domains then given by Λ TMG can be achieved by taking advantage of the well-defined fluence window for which AOS is observed.…”

The soft X-ray and XUV split-and-delay unit at beamlines FL23/24 at FLASH2

“…The requirements to perform such experiments are demanding and the key parameter to access the dynamics under investigation is the time evolution of the system. In the past many experiments have been carried out to examine the dynamics in atoms (Radcliffe et al, 2012;Ding et al, 2019), molecules (Krikunova et al, 2012a;Schnorr et al, 2014;Liekhus-Schmaltz et al, 2015;Lehmann et al, 2016;Hollstein et al, 2019;Rebholz et al, 2021), clusters (Krikunova et al, 2012b;Ferguson et al, 2016;Oelze et al, 2017;Asmussen et al, 2022), hot dense matter (Zastrau et al, 2014) and condensed matter systems (Inoue et al, 2016;Pardini et al, 2018;Roseker et al, 2018;Vinko et al, 2020;Liu et al, 2021). Results on time-resolved imaging (Gu ¨nther et al, 2011;Rath et al, 2014), spectro-temporal characterization of XUV pulses (Ding et al, 2021) and stimulated X-ray emission (Kroll et al, 2020) have also been reported.…”