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FMR spectroscopy is widely used for the characterization of many types of magnetic materials for use in an extensive range of applications. It is a powerful tool for probing both the magnetic properties and physical aspects of a material. In recent years in particular, there has been some interest in its use to study commercial recording media. However, there are a number of limitations inherent in the conventional method of observing FMR that restricts its usefulness and popularity as a research technique. The high, single frequency operation of the spectrometer makes broadband, frequency dependent measurements and studies of the unsaturated state of materials impractical. It also severely limits the quantity of data available making the analysis and interpretation difficult and prone to error. Additional complexities are encountered since the swept field technique means that a sample is subjected to a constantly changing magnetic environment which may not be ideal, especially for broad linewidth materials. A need, therefore, has been identified for an FMR technique capable of producing both swept field and swept frequency spectra over a wide range of frequencies. The design and development of a novel broadband FMR spectrometer is described in this thesis. The new technique has several advantages over similar methods presented in the literature. It can be applied over a very wide frequency range, dependent on the types of materials, for a variety of different FMR studies. The spectrometer itself is straightforward and easy to use and the resulting spectra (which show excellent agreement with equivalent conventional data) may be interpreted using the same models already used in FMR research. Most importantly, the simplicity of this spectrometer design means that it can be readily implemented in any reasonably equipped magnetics or microwave laboratory without the need for specific expertise or equipment. A preliminary broadband FMR study of magnetic recording media demonstrates the potential of the new technique both for more detailed characterizations of magnetic materials and for greater understanding of the ferromagnetic resonant effect itself. |
