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978-3-8439-1186-3, Reihe Physik
Three-Dimensional Tubular Spin-Wave Resonator Systems
136 Seiten, Dissertation Universität Hamburg (2013), Softcover, A5
This thesis studies the spin-wave eigenmodes in three-dimensional tubular spin-wave resonator systems with typical diameters of d = 3µm. The employed experimental techniques were broadband microwave absorption spectroscopy and time-resolved scanning Kerr microscopy. The detected modes are explained by constructive azimuthal spin-wave interference. The corresponding resonance frequencies can be tailored by changing the geometry of the magnetic structures, the orientation of the external magnetic field and the orientation of the excitation fields with respect to the specimen.
In particular, three core topics are investigated:
• Azimuthal spin-wave interference in rolled-up permalloy microtubes
In rolled-up permalloy films with spiral-shaped cross sections which were fabricated by a self-rolling mechanism, characteristic resonances are found which are explained by azimuthal spin-wave interference. The resonances occur both in longitudinally and transversally magnetized samples and can be well described by an analytical model. Therein, periodic boundary conditions along the azimuthal direction and an effective thickness parameter are introduced to model the coupling effects between the overlapping sections in the rolled-up structure. By transversely magnetizing the sample, the degeneracy of the first order mode is lifted. This behavior is found to be tuneable.
• Azimuthal spin-wave interference in permalloy coated needles
In experiments on permalloy coated needles, which consist of only one magnetic layer and do not show the spiral-shaped cross section of rolled-up films, characteristic modes are found which resemble the data obtained from rolledup permalloy films. The resonance spectra obtained from needles with different radii are well described by the analytical model for azimuthal spin-wave interference using the actual thickness of the coated permalloy.
• Spin-wave confinement in rolled-up permalloy microstripes
Arrays of multiple and identical rolled-up permalloy stripes of the width w are investigated and the obtained resonance frequencies are modeled analytically. These resonance frequencies are found to be dependent on the width of the rolled-up stripes. For stripe arrays with widths above w = 1.5 µm, the mode frequency of the azimuthal modes is found to be shifted to lower frequencies by the stripes’ transversal demagnetization influence.