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UBC Theses and Dissertations

Microwave responses of strongly demagnetized metallic samples Branch, Timothy William


The microwave magnetic responses of realistic, strongly-demagnetized hexagonal platelet samples were studied using numerical simulations in COMSOL Multiphysics®, in the context of cavity bolometric and cavity perturbation experiments. The effects of sample conductivity and edge rounding on this response are investigated in detail. Emphasis was placed on the specific sample geometries, material conductivities, and measurement frequencies of previously-performed cavity bolometric broadband measurements of palladium cobaltate (PdCoO₂) samples. Simulations of samples with finite conductivity in three dimensions presented numerical difficulties, which prevented the direct determination of the microwave responses of realistic hexagonal samples to sufficient accuracies. Therefore, a two-step approach was used to arrive at experimentally relevant results. As a first step, perfectly conducting, sharp-edged hexagonal platelet samples were simulated with geometry-necessitated three-dimensional models, as this case allowed the response within the sample bulk to be completely ignored; this in turn greatly reduced model complexities and enabled the response to be determined to high precision. As a second step, two-dimensional axisymmetric models were used to accurately simulate the responses of disks with both finite skin depths and finite edge radii. Comparing the responses of realistic disks to those of perfectly conducting, sharp-edged disks made it possible to estimate the relative reduction in sample power dissipation as a function of both the skin depth and of sample edge radius. By direct analogy between the disk and hexagonal samples, these two threads were woven to provide estimates of the power dissipation of the PdCoO₂ samples that were studied in the broadband experiments.

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