Magnetization Dynamics in Ultrathin Films and Multilayers

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University of Alabama Libraries

Robust understanding of magnetization dynamics is very crucial to design and fabricate novelmaterials for next generation spintronic applications. A combination of experimental techniques and theoretical modeling facilitates fundamental research to establish new concepts. This dissertation discusses the magnetization dynamics of ultrathin films and multilayers using broadband ferromagnetic resonance (FMR) techniques and micromagnetic simulations. Chapter one includes the theoretical background on magnetization dynamics, the explanation of FMR experiments with schematic diagrams and data analysis, and insight in micromagnetic simulations using the in-house developed MATLAB-based code M^3. All simulations are performed with M^3. Chapter one also includes a summary of various publications which I co-authored during my time as a graduate student in the Mewes’ Magnetics Laboratory at UA. Chapter two discusses the limitations of the macrospin model of materials with inhomogeneous perpendicular anisotropy. This is a micromagnetic study motivated from experimental FMR measurements of [Co/Ni]_N multilayers. Chapter three is devoted to experimental FMR measurements carried out on FeGa thin films. These results show significantly lower Gilbert damping and linewidth in comparison to previous publications in similar structures, indicating the high quality of these thin films. This is also confirmed by X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements. These films are particularly interesting because of their well known superior magnetostrictive behavior. Motivated from previous FMR experiments in IrMn/CoFe and MnN/CoFeB exchange bias systems, we investigated the anisotropic damping in multilayer spintronic devices using micromagnetic simulations in chapter four. With the introduction of a damping tensor in the Landau-Lifshitz- Gilbert (LLG) equation, this study explains the observed unidirectional relaxation in IrMn/CoFe bilayers and co-existence of unidirectional and uniaxial relaxation in MnN/CoFeB bilayers .

Electronic Thesis or Dissertation
Ferromagnetic Resonance, Magnetization dynamics, Micromagnetics, Multilayers, Spintronics, Thin films