ABSTRACT
Laser-driven non-local electron dynamics in ultrathin magnetic samples on a sub-10 nm length scale is a key process in ultrafast magnetism. However, the experimental access has been challenging due to the nanoscopic and femtosecond nature of such transport processes. Here, we present a scattering-based experiment relying on a laser-induced electro- and magneto-optical grating in a Co/Pd ferromagnetic multilayer as a new technique to investigate non-local magnetization dynamics on nanometer length and femtosecond timescales. We induce a spatially modulated excitation pattern using tailored Al near-field masks with varying periodicities on a nanometer length scale and measure the first four diffraction orders in an x-ray scattering experiment with magnetic circular dichroism contrast at the free-electron laser facility FERMI, Trieste. The design of the periodic excitation mask leads to a strongly enhanced and characteristic transient scattering response allowing for sub-wavelength in-plane sensitivity for magnetic structures. In conjunction with scattering simulations, the experiment allows us to infer that a potential ultrafast lateral expansion of the initially excited regions of the magnetic film mediated by hot-electron transport and spin transport remains confined to below three nanometers.
ABSTRACT
We present experimental data and a complete theoretical description of the magneto-optical contributions to the complex refractive index in the extreme ultraviolet (XUV) range covering the 3p resonances of Fe, Co, and Ni. The direct comparison of the two allows us to conclude that many-body corrections to the ground state and local field effects are crucial for an accurate description of M-edge spectra. Our results are relevant for investigation of static magnetization, via XUV spectroscopy of multielement systems, as well as the dynamics of magnetization, as needed in the study of femtomagnetism and spintronics.
