ISBN 9783843928052

978-3-8439-2805-2, Reihe Physik

Matthias Pues
Magnetic microscopy and spectroscopy of excitations in nanostructured ferromagnetic alloys

129 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5

Zusammenfassung / Abstract

Research of micromagnetism and the effects of micro- and nanoscopic structures is vital for the realisation of new magnetic data-storage devices and new concepts of data-processing.

In this thesis ferromagnetic absorption spectroscopy as well as several imaging methods are used for the investigations on magnetic phenomena in two ferromagnetic alloys. Magnetic force microscopy and optical wide-field Kerr microscopy are complementary for the investigation of magnetic thin films with different spatial dimensions, whereas magnetic X-ray transmission microscopy is used for additional element specific information. The dynamics of isolated magnetic antivortices are studied by high-frequency absorption spectroscopy. To be able to perform this kind of ensemble measurement, a method for the reliable generation of the magnetic singularities is devised with a specially formed microstructure and a two-dimensional sequence of a magnetic field. The experiments show that the resonance frequency of antivortices is lower than for comparable vortices. Similarly to the spectroscopy on vortices, a characteristic absorption cone signal is found for antivortices for high excitation powers. This indicates the continuous switching of the antivortex core. The deflection of the antivortices by an external field reveals strong deviations from a confining harmonic potential, as well as very low annihilation fields.

Furthermore, the effects of lateral patterning on thin films with a perpendicular magnetic anisotropy are investigated. The coercive field of the perpendicularly magnetised films is found to be sensitive to lateral patterning. Sharp tips of nanowires facilitate a switching at low fields compared to blunt or bulbous end geometries. This knowledge is applied in a method to generate magnetic bubble domains in circular structures by external field pulses. These magnetic singularities in out-of-plane magnetised materials are of an emerging interest as possible candidates for data storage, similar to vortices and antivortices in in-plane films.