Dynamics of magnetic vortices and antivortices studied by ferromagnetic absorption spectroscopy and transmission x-ray microscopy

Magnetic singularities in micron-sized ferromagnetic elements have been proposed for new concepts of magnetic data storage and are an ideal model system for the investigation of magnetization dynamics. This thesis deals with the dynamics of magnetic vortices as well as antivortices at picosecond and nanosecond timescales. High frequency alternating fields and spin-polarized currents are used for the manipulation of the vortices' magnetic states. The special case of rotational excitation is investigated by time-resolved magnetic transmission x-ray microscopy, micromagnetic simulations, and analytical calculations. For magnetic antivortices we find an asymmetric response to field and current excitation that we can explain with the negative winding number of their domains. In addition, we study the dynamics of magnetic vortices in the frequency domain by means of ferromagnetic absorption spectroscopy. We find deviations from the linear dynamics that we assumed previously. These deviations are explained in the context of a nonparabolic confining potential and a critical maximum velocity of vortex motion. Absorption spectra are found to be crucially influenced by the continuous reversal of the vortex-core polarization for high amplitudes of excitation. The insight into vortex dynamics gained in this work is crucial for a successful application of vortices for data storage devices.

Magnetische Singularitäten in mikroskopisch kleinen, ferromagnetischen Dünnfilmelementen könnten in der Zukunft in magnetischen Speichermedien Verwendung finden. Des Weiteren stellen sie ein ideales Modellsystem für die Untersuchung der Magnetisierungsdynamik dar. Diese Arbeit behandelt die Dynamik magnetischer Wirbel, der sogenannten Vortizes und Antivortizes, auf Zeitskalen von wenigen Pikosekunden bis zu mehreren Nanosekunden. Hochfrequente magnetische Wechselfelder und spin-polarisierte Ströme werden genutzt um die magnetischen Zustände dieser Strukturen gezielt zu verändern. Mittels