Graduate Thesis Or Dissertation


Ultrafast Dynamics of Magnetic Multilayer Films: Magneto-Optical Spectroscopy and Resonant Scattering in the Extreme Ultraviolet and Soft X-Ray Spectral Regions Public Deposited
  • This thesis focuses on studying ferromagnetic thin films with high temporal and spatial resolution using tabletop extreme ultraviolet (EUV) light sources based on high harmonic generation (HHG) and ultrafast soft X-rays from a free-electron laser. In Chapter 4, a new magneto-optical technique is developed. It allows a direct measurement of the full resonant complex EUV magneto-optical permittivity on a tabletop and thus, through a comparison with first principles calculations, is capable of capturing the microscopic mechanisms of ultrafast laser-induced demagnetization. It is found that, in Co, the demagnetization response is dominated by magnon excitations with possible smaller contributions from other mechanisms. Chapter 5 discusses the development of an efficient approach for resonant magnetic scattering (RMS) with a tabletop HHG source. This approach is used to study magnetic textures with spatial resolution. In an external magnetic field, a transition from a disordered network of stripe domains to an ordered lattice of magnetic vortices is observed in an Fe-Gd thin film. Chapter 6 presents the results of a dynamic soft X-ray RMS experiment on a disordered domain network performed at the Linear Coherent Light Source (LCLS). By directly applying the experimental data to a carefully simulated domain pattern, laser-induced transient changes in the domains are captured in real space, and strong non-uniformities in the demagnetization across the sample are observed. These non-uniformities are attributed to a combined effect of ultrafast spin-polarized currents and a gradient in the pump absorption throughout the thickness of the sample. Chapter 7 provides an outlook towards time-resolved lensless magnetic spectro-microscopy with HHG sources.
Date Issued
  • 2018
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Last Modified
  • 2019-11-15
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