Magnetization Dynamics in Thin Film and Multilayer Structures
2022-06
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Magnetization Dynamics in Thin Film and Multilayer Structures
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2022-06
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Abstract
Spintronics is a field of research that seeks to exploit the spin rather than the charge ofthe electron for information-technology applications, with the promise of computational
devices that use less energy while being faster and more powerful. A major challenge
in this field has been the understanding and control of how the energy contained in a
system of electron spins is transferred, and ultimately lost, to the rest of the material.
This thesis presents experimental measurements of magnetization damping using ferromagnetic
resonance in a variety of different thin films and multilayer structures, along
with unique ways of understanding the physical mechanisms that cause damping.
First, the effect of an extrinsic two-magnon scattering mechanism on the magnetization
damping is demonstrated in a series of Heusler alloy thin films. A model of
two-magnon scattering is developed to fit the data, and particular emphasis is placed
on the mechanisms which cause the effect to be stronger in the Heusler films. It is then
shown how two-magnon scattering can shift the resonance frequency, an effect that is
almost always neglected, which is important due to the ubiquity of using ferromagnetic
resonance measurements to extract magnetic anisotropy energies. The following portion
of the thesis deals primarily with magnon-phonon coupling and its effect on damping.
A mechanism of magnetization damping due to magnon-phonon coupling is shown to
dominate the overall damping in a series of Fe0.7Ga0.3 alloy thin films. The mechanism
causes a giant anisotropy of the damping, with the damping coefficient varying
by as much as a factor of 10 depending on the orientation of the magnetization. This
mechanism is extrinsic, and so it is important to account for when measuring the intrinsic
damping of a material. Finally, a phonon pumping mechanism is demonstrated
in a series of Co/Pd multilayers. Phonon pumping causes a resonant damping of the
magnetization dynamics, at a frequency that is determined by the total thickness of
the multilayer. The temperature dependence is much stronger than expected, which
underscores the importance of magnetic boundary conditions in the problem. There is
also a resonance frequency shift that accompanies the resonant damping, which can be
predicted accurately using linear response theory.
Description
University of Minnesota Ph.D. dissertation. June 2022. Major: Physics. Advisor: Paul Crowell. 1 computer file (PDF); viii, 109 pages.
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Peria, William. (2022). Magnetization Dynamics in Thin Film and Multilayer Structures. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/241608.
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