Physical Review Letters ( IF 8.385 ) Pub Date : 2020-09-15 , DOI: 10.1103/physrevlett.125.127201
Michael Schneider; Bastian Pfau; Christian M. Günther; Clemens von Korff Schmising; David Weder; Jan Geilhufe; Jonathan Perron; Flavio Capotondi; Emanuele Pedersoli; Michele Manfredda; Martin Hennecke; Boris Vodungbo; Jan Lüning; Stefan Eisebitt

We systematically study the fluence dependence of the resonant scattering cross-section from magnetic domains in Co/Pd-based multilayers. Samples are probed with single extreme ultraviolet (XUV) pulses of femtosecond duration tuned to the Co ${M}_{3,2}$ absorption resonances using the FERMI@Elettra free-electron laser. We report quantitative data over 3 orders of magnitude in fluence, covering $16\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{mJ}/{\mathrm{cm}}^{2}/\mathrm{pulse}$ to $10\text{\hspace{0.17em}}000\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{mJ}/{\mathrm{cm}}^{2}/\mathrm{pulse}$ with pulse lengths of 70 fs and 120 fs. A progressive quenching of the diffraction cross-section with fluence is observed. Compression of the same pulse energy into a shorter pulse—implying an increased XUV peak electric field—results in a reduced quenching of the resonant diffraction at the Co ${M}_{3,2}$ edge. We conclude that the quenching effect observed for resonant scattering involving the short-lived Co 3p core vacancies is noncoherent in nature. This finding is in contrast to previous reports investigating resonant scattering involving the longer-lived Co 2p states, where stimulated emission has been found to be important. A phenomenological model based on XUV-induced ultrafast demagnetization is able to reproduce our entire set of experimental data and is found to be consistent with independent magneto-optical measurements of the demagnetization dynamics on the same samples.

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