ISBN 978-3-8439-3561-6

978-3-8439-3561-6, Reihe Physik

Markus Rollinger
Investigation of magnetic and magneto-plasmonic effects via photoemission electron microscopy

154 Seiten, Dissertation Technische Universität Kaiserslautern (2018), Softcover, A4

Zusammenfassung / Abstract

This thesis transfers the concept of using magnetic circular dichroism (MCD) in the x-ray regime to image magnetic domain structures in the visible part of the electromagnetic spectrum with photoemission electron microscopy (PEEM). For TbCo, a rare earth - transition metal alloy, which is known for all-optical switching of magnetic domains, the MCD of a bare film is well understood. From a technological point of view, however, the capping layer must stay intact. The additional capping layer on top of the magnetic layer preserves the shape of the magnetic domains but inverts its contrast. This is contrary to the conventional assumption that an increasing capping layer without inherent MCD only decreases the overall asymmetry. We investigate the energy-resolved MCD spectra with capping layers of different thicknesses and materials, e.g. Al, Pt or MgO. It turns out that the MCD magnitude is almost energy independent for the capped samples and they hardly differ from each other quantitatively. Based on FDTD calculations the electric field profile of light and its absorption within the multilayer stack of the sample is simulated. Differences emerge between a model which adequately describes pure optical MCD measurements and one that takes into account that photoemitted electrons with a finite escape depth are used as a probe for MCD. It even allows to reproduce the inversion of the contrast upon comparison of capped and uncapped samples.

For the magneto-plasmonic sample, PEEM has the capability to image micro- and nanostructured samples in real space as well as their electric near-field distribution. The latter can be significantly modified by the excitation of propagating or localized plasmons. Here, an amorphous Ni film with a hexagonal array of holes is investigated. Precise correlations between the observable amplification of the electric near-field of microstructured surfaces due to plasmons and the enhanced rotation measured in polar magneto-optical Kerr effect (MOKE) measurements are conducted for varying polarization states and wavelengths of light. It is shown that the enhanced Kerr rotation cannot be explained by the drop in reflectivity alone.

Combining both parts of the thesis leads to the possibility to measure magnetic and plasmonic properties within the same experiment for such magneto-plasmonic structures. It paves the way to investigate dynamically how the excitation of plasmons influences the magnetic system or vice versa.