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Author: Schick, Daniel × DDC: 500 ×

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    Optical inter-site spin transfer probed by energy and spin-resolved transient absorption spectroscopy
    ([London] : Nature Publishing Group UK, 2020) Willems, Felix; von Korff Schmising, Clemens; Strüber, Christian; Schick, Daniel; Engel, Dieter W.; Dewhurst, J. K.; Elliott, Peter; Sharma, Sangeeta; Eisebitt, Stefan
    Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems.
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    Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity
    (Melville, NY : AIP Publishing LLC, 2021) Chardonnet, Valentin; Hennes, Marcel; Jarrier, Romain; Delaunay, Renaud; Jaouen, Nicolas; Kuhlmann, Marion; Ekanayake, Nagitha; Léveillé, Cyril; von Korff Schmising, Clemens; Schick, Daniel; Yao, Kelvin; Liu, Xuan; Chiuzbăian, Gheorghe S.; Lüning, Jan; Vodungbo, Boris; Jal, Emmanuelle
    During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm (≃310 eV), we were able to probe close to the Fe L3 edge (706.8 eV) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.