Dynamics of Functional Magnetic Microstructures

Holländer, Rasmus Bahne

This work is about the dynamics of functional magnetic microstructures. In the beginning it contains research on numerical modeling the motional response of superparamagnetic microbeads on top of patterned ferromagnetic surfaces. At first, an expression for the potential energy of the system is derived. After this, the details of the numerical modeling are explained, followed by a comparison to experimental data. Furthermore, a specialized microscope setup is discussed, which allows for performing stroboscopic measurements with picosecond time resolution. Based on this experimental setup the possibility of dynamic vector microscopy was investigated for the differential measurement of localized individual magnetization components. Then, switchable magnetization dynamics via magnetic domain states at zero-field is investigated. An asymmetric structure is used, which breaks the symmetry of the two remanent states by field history along the hard and easy axis of uniaxial anisotropy. In particular, the utilized specimen is investigated by pulsed inductive microwave magnetometry and dynamic magneto-optical vector microscopy. Here, switchable high-frequency properties result from local ferromagnetic resonances. The last part is then about the excitation of magnetostatic spin waves and elastic waves, visible in the dynamic magnetization. Here, a simplified two dimensional micromagnetic model is used for comparison to the high frequency experiments. The observed magnetostatic spin waves coincide for experiment and model. The experimentally observed elastic waves coincide with the phase velocity, calculated under assumption of literature values.

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Holländer, Rasmus: Dynamics of Functional Magnetic Microstructures. 2019.

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