New soft magnetic materials for high frequency applications

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University of Alabama Libraries

Soft magnetic materials are widely used in devices such as inductors, transformers, antennas, magnetic hard drives, etc. Some of those devices will benefit greatly from operating at high frequencies. Thus fundamental study on finding the materials that have better soft magnetic properties is essential for improving the performance of those devices. Fe alloys have been proved to be promising candidates for high frequency applications. In this dissertation, an extensive study of magnetic properties of FeAl, (FeCo)-Al and (FeCo)-Si alloy thin films and their dependence on the film thickness and growth temperature has been presented. These films have body-centered cubic structure and columnar growth morphology. It is shown that the thickness of the film, which has an influence on the stress inside the film, may affect the coercivity through the magnetic-elastic coupling. The same mechanism is observed in the growth temperature dependence study, where reduced stress caused by increased growth temperature leads to a decrease in coercivity. The effective damping parameter shows a huge increase at small thickness due to the spin pumping effect. In-plane rotation ferromagnetic resonance measurements unveil the existence of four-fold anisotropy in (FeCo)-Si films. In addition, a four-fold symmetry is observed in the FMR linewidth vs. in-plane angle plot, which indicates anisotropic damping caused by the two-magnon scattering contribution. The film thickness dependence of FMR linewidth caused by the two-magnon scattering suggests that the origin of the two-magnon scattering is not pure interfacial.

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