X-ray specular and off-specular diffuse scattering of magnetic interface structures at XFEL sources - investigating ultrafast spin transport processes
Final Report Abstract
In this project studies have been performed pioneering experiments at the FEL sources FERMI and FLASH and demonstrated the feasibility of resonant magnetic reflectivity experiments at FEL sources. At the first stage of this project, the reflectivity setup at FERMI was constructed and was performed the test experiments at FERMI in collaboration with the FERMI team. After successfully completing this stage, we analyzed data with regards to spin and interface morphology information and compare the different interface systems with regards to difference in the spin transport properties In those experiments we achieved the following milestones: X-ray resonant magnetic reflectivity. We measured ultrafast resonant magnetic X-ray reflectivities as a function of the surface-normal wavevector transfer Qz yielding depth-resolved information about spin and charge density profiles. In this experiment, we demonstrated the reliable switching of polarization states between left and right-handed light at a FEL source and used this to measure the magnetic asymmetry of a magnetic multilayer system. Furthermore, we were able to measure at selected points in reciprocal space ultrafast IR pump XUV probe reflectivities with a temporal resolution of 100 fs. Ultrafast magnetic scattering experiments. Making use of the surface sensitivity of X-rays under shallow angles, we investigated the spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We observed a magnetization-reversal close to the domain wall boundaries that becomes more pronounced closer to the Al/FM film interface. This magnetization-reversal is driven by the different transport properties of the majority and minority carriers through a magnetically disordered domain network. Its finite lateral extension has allowed us to determine the ultrafast spindiffusion coefficients and ultrafast spin velocities for the majority and minority carriers upon IR excitation. Fluence dependent resonant X-ray reflectivity. Superradiant resonant effects may reduce the intensity necessary for observing nonlinear processes such as X-ray induced transparency or stimulated emission by many orders of magnitude, especially for photon energies in the XUV regime. We measured the fluence dependence of ultrafast XUV resonant reflectivities of a Permalloy(Py)/Ta/Permalloy(Py) trilayer system with the FEL photon energy resonantly tuned to the Ni M2,3 edge. The experiment revealed a lower bound for the threshold fluences at which superradiant non-linear processes play a dominant role in the fluence dependence of XUV reflectivities at the M-edges.
Publications
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Scientific Reports 7, 15064 (2017)
T. Sant et al.
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Structural Dynamics 4, 055101 (2017)
C. Gutt et al.
