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Ultrafast demagnetization dominates fluence dependence of magnetic scattering at Co M edges

Schneider, Michael; Pfau, Bastian; Günther, Christian M.; Korff Schmising, Clemens von; Weder, David; Geilhufe, Jan; Perron, Jonathan; Capotondi, Flavio; Pedersoli, Emanuele; Manfredda, Michele; Hennecke, Martin; Vodungbo, Boris; Lüning, Jan; Eisebitt, Stefan

Inst. Optik und Atomare Physik

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 M3,2 absorption resonances using the FERMI@Elettra free-electron laser. We report quantitative data over 3 orders of magnitude in fluence, covering 16  mJ/cm2/pulse to 10 000  mJ/cm2/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 M3,2 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.