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978-3-8439-2938-7, Reihe Physik
Control of spin-wave propagation
125 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5
In this thesis the redirection and manipulation of spin waves by means of refraction and diffraction are investigated experimentally and by micromagnetic simulations. The particular propagation anisotropy of spin waves leads to unique effects and is exploited to control the propagation of spin waves.
Spin waves at step like thickness variations in ferromagnetic permalloy films were investigated experimentally. Upon impinging onto a thickness step, spin waves are either subject to refraction or reflection at the step. The generalized Snell’s law is employed to describe both cases. By changing the orientation of an in-plane external magnetic field the anisotropy axis can be tilted, hence enabling switching from refraction to total reflection. Furthermore, a new type of confined spin wave is observed and explained by gradual refraction at a gradient of the internal magnetic field.
Based on refraction at thickness steps, a focusing spin-wave lens is designed, constructed and experimentally investigated. Due to the spin-wave anisotropy a particular lens shape is required. A numerical procedure was devised to find the according lens shape. Due to the anisotropy, three different geometries qualify as focusing lenses. Of these geometries, one design was realized and the focusing character experimentally validated. Importantly, the developed lens-design procedure is transferable to other waves in anisotropic media.
The concept of refraction was applied to temporal variations of the medium, specifically variations of an external magnetic field. By breaking the time invariance, the energy conservation for spin waves is lifted and the spin-wave frequency can be altered. By means of micromagnetic simulations the stopping and rebound of Backward-Volume spin-wave packets is demonstrated. The application of the concept is proposed to arbitrarily and remotely control the propagation of spin-wave packets.
A design for a spin-wave bandpass-filter based on the Talbot effect for spin waves is investigated experimentally and by micromagnetic simulations. In addition to spin-waves guided by refraction, dipole-dipole coupling across the filter as well as a non-propagating oscillation of the magnetization and spin waves excited at the filter are identified as contributions to the measured signal behind the filter.