ISBN 9783843938792

978-3-8439-3879-2, Reihe Physik

Carolin Behncke
Control of crystal properties in coupled vortex systems

144 Seiten, Dissertation Universität Hamburg (2018), Softcover, A5

Zusammenfassung / Abstract

Ferromagnetic disks in the vortex state are promising candidates for applications such as future signal processing, data storage, or logic devices. In this work, two- and three-dimensional arrangements of magnetic vortices are investigated. The static and dynamic behavior of the coupled vortex systems is studied using three complementary measurement methods, i.e., scanning transmission x-ray microscopy, magnetic force microscopy, and ferromagnetic absorption spectroscopy. The experimental findings are compared to calculations based on a rigid particle model for the magnetic vortex and to micromagnetic simulations. In the first part of this thesis, two-dimensional arrangements consisting of hundreds of vortices are investigated in the context of their behavior as magnonic crystals. Collective oscillations of the fundamental excitation mode of the vortices are examined. The resonance frequency of such an excitation of the so-called gyrotropic mode lies in the sub-gigahertz range. In different crystal lattices various crystal properties are determined, i.e., the dispersion relation, the magnetic ordering, and the emergence of geometrical frustration. The influence of the polarization state on these crystal properties is studied. As the polarization patterns can be tuned dynamically, the manipulation of the polarizations can be understood as a dynamic control of the crystal properties. In the second part of this work, three-dimensional arrangements of magnetic vortices are investigated. Higher-order excitations with frequencies in the gigahertz regime lead to the emission of spin-waves by the vortex cores. The spin waves have a linear dispersion relation with wavelengths down to the sub-100 nm range. In the investigated vortex systems, the spin-wave properties can be controlled including the wavelength, the propagation direction, and the spatial confinement. The experiments are in excellent agreement with micromagnetic simulations. The understanding and control of the spin-wave properties is crucial for the application of spin-waves in future spintronic devices.