Element-specific detection of magnetization dynamics using Scanning Transmission X-ray Microscopy

In this thesis, the magnetization dynamics of micro- and nanometer-sized samples were element specifically and spatially resolved (< 50 nm) measured by Scanning Transmission X-ray Microscopy detected Ferromagnetic Resonance (STXM-FMR), which offers time-resolved measurements at < 20 ps.

STXM-FMR has clarified the origin of resonances in a Py/Co disk/stripe bilayer mi- crostructure (2.5 μm × 30 nm/2 μm × 0.5 μm × 30 nm) detected by conventional Fer- romagnetic Resonance (FMR). Uniform resonances in Py and Co and an exchange coupled resonance of both constituents are revealed. The element-specific measure- ments at the Ni L3 and Co L3 X-ray absorption edges showed an angular momentum transfer from Py to Co and vice versa at the Py and Co resonance, respectively. At the coupled resonance, an enhanced precession cone of the magnetization could be shown. Due to an amplitude and phase analysis of the STXM-FMR data at the Co L3 edge, an inhomogeneous excitation of the stripe due to the stray field influence at the stripe edges could be revealed. Uniform and non-uniform spin waves have been investigated by STXM-FMR for a single Py stripe (5 μm × 1 μm × 30 nm) and for two stripes with the same dimensions in T- and L- shaped geometries, showing a di- rected oscillatory behavior of the modes. These unexpected observations are con- firmed by micromagnetic simulations. They are attributed to the stray field distri- bution, which results in the excitation of additional resonant modes at the stripe edges, which generate a phase gradient of the magnetization causing the spin wave modes’ directed oscillation.

STXM-FMR measurements of Yttrium Iron Garnet nanoparticles revealed a distribu- tion of excitations with different phase in the investigated YIG particle agglomerate. For the first time the resonant response of segments of a bi-segmented Fe3O4 nano- particle chain with a spatial resolution of < 50nm could be element-specifically and spatially resolved measured.


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