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978-3-8439-1299-0, Reihe Physik
Hauke H. Langner
High-Frequency Detection of Magnetic Vortices
101 Seiten, Dissertation Universität Hamburg (2013), Softcover, A5
The dynamics of vortices in thin soft-magnetic films are investigated. Squared microstructures are used as examination objects in which so-called Landau-domain patterns are formed. With high-frequency magnetic fields vortices are forced into a gyrotropic motion. The vortices are studied by means of spectroscopic methods as well as via transmission X-ray microscopy.
In an analytic treatment the vortex can be understood as quasiparticle for which an equation of motion can be formulated. The calculations for squared microstructures are performed via parabolic potentials with fourth order corrections. Resonantly excited vortices, deflected by static external magnetic fields to the border of the microstructure, have ellipse-like trajectories. The trajectories are measured with time-resolving X-ray transmission microscopy. The shapes of the trajectories give information about the confining potential of the vortex. The coincidence between measured trajectories and trajectories calculated from the predicted potential justify the use of the quasiparticle model.
The frequency of the magnetic field that excites the vortex resonantly is determinable by spectroscopic measurements. A method in which the Faraday's law of induction is utilized to examine single microstructures spectroscopically is presented. The change of the stray fields of the magnetization pattern is detected with a micrometer scaled induction loop. With the help of inductive measurements on single elements influences on the resonance frequency of the vortex, originating from irregularities in the microstructure, are resolved. The measured spectra are described analytically.
The implantation of foreign atoms leads to an increase of magnetic damping in the microstructure. As consequence of the higher damping vortex trajectories are observed that exhibit an eccentricity. The equation of motion for the vortex predicts the observed phenomenon. Two inclinations of the elliptical vortex trajectories exist that depend on the polarization of the vortex core. Further local modifications are prepared by material implantation on another squared microstructure. Beside changed magnetic parameters the implantation is accompanied by a slight reduction of the film thickness. The microstructure is prepared so that at resonant excitation the vortex passes both the implanted and the non-implanted region in one cycle. With time-resolving transmission X-ray microscopy a drastic change of the vortex velocity is observed.