Unraveling Femtosecond Spin and Charge Dynamics with EUV T-MOKE Spectroscopy

von Henrike Probst
Dissertation
Datum der mündl. Prüfung:2023-08-21
Erschienen:2023-12-15
Betreuer:Prof. Dr. Stefan Mathias
Gutachter:Prof. Dr. Stefan Mathias
Gutachter:Prof. Dr. Martin Wenderoth
Zum Verlinken/Zitieren: http://dx.doi.org/10.53846/goediss-10256

 

 

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Englisch

In this thesis, a novel transverse magneto-optical Kerr effect (T-MOKE) setup with extreme ultraviolet light from high-harmonic generation between 30 and 72 eV is used to study the spectrally-resolved spin and charge dynamics of the 3d ferromagnets Ni, Co and Fe after femtosecond (fs) laser excitation. The focus of the study is on the dynamics that occur during or shortly after the optical excitation (<100 fs), when the electron system is in a far-from-equilibrium state. In particular, an intriguing effect is studied, where under almost identical experimental conditions, apparently contradictory dynamics are observed in the spectrally-resolved analysis of the transient T-MOKE asymmetry of Ni. As a consequence, it is shown that the commonly analyzed magneto-optical asymmetry may show time-dependent behavior that is not directly related to the magnetic properties of the sample. To overcome this critical observation and to gain access to the true spin dynamics, a method is introduced to retrieve the time-dependent dielectric tensor as the property linking optical spectroscopy measurements to the electronic structure, allowing a direct comparison between experimental T-MOKE data and time-dependent density functional theory (TDDFT) calculations of electron and spin dynamics. Finally, differences and similarities in the spectrally-resolved spin and charge dynamics of the 3d ferromagnets are investigated, suggesting a classification of the dynamics in the context of strong and weak ferromagnetism.
Keywords: transverse magneto-optical Kerr effect; ultrafast magnetism; 3d ferromagnets; spin dynamics; electron dynamics; dielectric tensor; extreme ultraviolet light; TDDFT
 
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