Graduate Thesis Or Dissertation
 

Determination of magnetoelastic parameters in magnetic thin films from FMR spectra

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9880w024r

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  • The ferromagnetic resonance (FMR) phenomenon serves as a sensitive probe of the effective internal fields in a magnetic material. FMR spectroscopy has consequently become a well-established technique, extensively employed in assessing material properties such as magnetic anisotropy, Landé g-factor, damping parameter, and the magnetoelastic constants of magnetic materials. Determining these material properties with high precision is required for the development of magnetic device technologies for radio frequency signal processing and magnetic data storage, as well as potential future applications in beyond-CMOS and quantum computation. In this work, we describe the development of a novel measurement system that combines angle-resolved FMR and strain-dependent FMR to accurately determine anisotropy and magnetoelastic constants of crystalline magnetic film samples. The capability to arbitrarily choose the angle of applied field with respect to the crystal axes allows for the determination of second-order and higher anisotropy constants while the application of strain to the sample enables the measurement of magnetoelastic effects. Uniquely in our approach, rotation of the sample in the strain fixture results in the introduction of shear strain in the sample, which is needed for full characterization of the magnetoelastic constants. Further, we describe an efficient fitting algorithm to extract the requisite set of material parameters from the FMR spectrometer data. The data are fit to a comprehensive model based on the Smit-Beljers equation, which calculates the FMR frequency for a given direction of magnetization, the material parameters, and the directions of applied field and strain. Since the orientation of the magnetization vector in the sample is unknowable until the material properties have been determined, this new approach iterates between estimation of internal magnetization and estimation of the material properties until a self-consistent solution is obtained. This integrated approach not only advances the understanding of anisotropy and magnetoelastic properties but also contributes to the broader goal of magnetic materials discovery to drive innovations in signal processing and computation devices. [N.B.: This thesis has been paraphrased and polished using the ChatGPT]
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