Ultrafast Dynamics of Magnetic Multilayer Films: Magneto-Optical Spectroscopy and Resonant Scattering in the Extreme Ultraviolet and Soft X-Ray Spectral Regions

Zusin, Dmitriy

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 Öffentlichkeit Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/k35694421

Abstract

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.

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