Magnetisation dynamics in ferromagnetic continuous and patterned films: microwave current injection ferromagnetic resonance, propagating spin waves, and a ferromagnetic resonance-based hydrogen gas sensor

Crosby Soon Chang

    Research output: ThesisDoctoral Thesis

    219 Downloads (Pure)

    Abstract

    [Truncated abstract] In recent years, microwave magnetisation dynamics in thin ferromagnetic metallic films, multi-layers, and nano-structures has attracted a lot of attention due to possible future applications in microwave signal processing, magnetic logic, and magnetic sensors. In this work, magnetisation dynamics were studied for ferromagnetic continuous and patterned films using inductive broadband spin wave spectroscopy techniques in three projects: a.) A microwave current injection ferromagnetic resonance (FMR) technique using a sub-millimetre coplanar probe was demonstrated on a continuous Permalloy film and a periodic array of Permalloy nano-stripes. It was found that the first standing spin wave mode (SSWM) with odd symmetry across the material thickness was efficiently excited in the nano-stripe array. On the contrary, in spin wave resonance spectra measured with conventional techniques the higher-order SSWMs are often lacking due to symmetry reasons. However, they are of great importance since they carry important information about the exchange constant for the material. Calculations of microwave current distributions by the current injection method were used to explain the spin wave resonance spectra. The suggested current injection FMR technique is fast and simple. On top of the efficient excitation of the higher-order SSWMs, it also allows spatial mapping of magnetisation dynamics with spatial resolution determined by the size of the coplanar probe tip. b.) Magnetostatic spin wave modes in the Damon-Eshbach geometry were systematically studied for a series of Permalloy micro-stripes over a wide range of aspect ratios using a highly sensitive custom-made microwave detector. The use of the detector allowed tracking the spin wave dispersion over a wide range of wave numbers using the simple phase method. It was found that over the range of aspect ratios and wave numbers studied, the dynamic effects can be neglected and the surface mode dispersions can be modelled by including an effective static demagnetising field term in the continuous film dispersion case. The group velocities were found to increase with thickness and were width invariant over the aspect ratios considered. The attenuation and relaxation parameters were found to be typical for the material. It was also found that the non-reciprocity parameter is largely invariant over the range of aspect ratios studied...
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2013

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