Breakdown of the X-Ray Resonant Magnetic Scattering Signal during Intense Pulses of Extreme Ultraviolet Free-Electron-Laser Radiation

We present results of single-shot resonant magnetic scattering experiments of $\mathrm{Co}/\mathrm{Pt}$ multilayer systems using 100 fs long ultraintense pulses from an extreme ultraviolet (XUV) free-electron laser. An x-ray-induced breakdown of the resonant magnetic scattering channel during the pulse duration is observed at fluences of $5\mathrm{J}/{\mathrm{cm}}^2$. Simultaneously, the speckle contrast of the high-fluence scattering pattern is significantly reduced. We performed simulations of the nonequilibrium evolution of the $\mathrm{Co}/\mathrm{Pt}$ multilayer system during the XUV pulse duration. We find that the electronic state of the sample is strongly perturbed during the first few femtoseconds of exposure leading to an ultrafast quenching of the resonant magnetic scattering mechanism.

Figure 1

Detector images showing the resonant magnetic scattering signal from a $\mathrm{Co}/\mathrm{Pt}$ magnetic multilayer film in which the magnetic domains have been partially aligned beforehand. The FEL has been tuned to the magnetodichroic transition of cobalt at 20.8 nm. (a) The sum of 1000 low-fluence images with a total flux of $7.5\mathrm{J}/{\mathrm{cm}}^2$. (b) Single-shot image using a high incident x-ray fluence of $5\mathrm{J}/{\mathrm{cm}}^2$. In both cases the color bar indicates the total number of scattered photons. The parasitic signal in the right-hand image originates from the explosion of the sample and is different in each single shot. The regular grid structure is due to a nickel-mesh stabilized aluminum filter protecting the camera from any visible light.

Figure 2

Probability density functions of the speckle intensity for the low- (blue) and high-fluence (red) speckle pattern from Fig. 1. The black solid lines are fits with Eq. (S1) (in the Supplemental Material) giving the number of modes $M$ contributing to the speckle image (see Supplemental Material [21]).

Figure 3

The azimuthally integrated resonant magnetic scattering signals from Fig. 1 normalized to the incident photon flux. The blue line represents the low-fluence measurement with $7.5\mathrm{mJ}/{\mathrm{cm}}^2$ and the red line the high-fluence measurement with $5\mathrm{J}/{\mathrm{cm}}^2$.

Figure 4

Simulation results of the evolution of the $\mathrm{Co}/\mathrm{Pt}$ multilayer system during the exposure to a 100 fs long FEL pulse. Fraction of differently charged cobalt ions at (a) low and (b) high FEL pulse fluences.

Figure 5

Simulation results of the kinetic temperature evolution of the free electrons of a $\mathrm{Co}/\mathrm{Pt}$ multilayer system during the exposure to a 100 fs long FEL pulse at the fluences used in the experiment.