Browsing by Author "Patton, Carl E., advisor"
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Item Open Access Nonlinear spin wave instability processes in manganese substituted zinc y-type hexagonal ferrites(Colorado State University. Libraries, 2010) Cox, Richard Garner, author; Patton, Carl E., advisor; Eykholt, Richard Eric, 1956-, committee member; Kabos, Pavel, committee member; Leisure, Robert Glenn, 1938-, committee member; Menoni, Carmen S., committee member; Robinson, Raymond S., committee memberThe large magnetocrystalline anisotropy observed in hexagonal ferrites makes these materials ideally suited for high frequency millimeter-wave applications. However, the large microwave losses observed at low-power levels and the high-power handling capabilities of hexagonal ferrites need to be addressed prior to their wide acceptance in real devices. In order to address the above issues, measurements and analyses of the microwave field amplitude (hcrit) required to parametrically excite nonlinear spin wave amplitude growth were performed on single crystal easy plane disks of Mn substituted Zn Y-type hexagonal ferrites at 9 GHz and room temperatures. Plots of the hcrit dependence on the static magnetic field, termed "butterfly curves," were obtained and analyzed for the resonance saturation (RA), subsidiary absorption (SA), and parallel pumping (PP) configurations. In order to obtain the butterfly curve data and perform the analyses: (1) a state-of-the-art computer-controlled high-power microwave spectrometer was constructed, (2) the classical spin wave instability theory, originally developed by Suhl and Schloemann, was extended, and (3) instability measurements were performed on multiple Zn Y-type hexagonal ferrites samples for several pumping configurations and static field settings. The measurements and analyses performed here constitute the first time RS, SA, and PP spin wave instability butterfly curve analysis have all been performed in planar hexagonal ferrite samples. This work also corresponds to the first time that resonance saturation measurements and analyses were performed for static magnetic fields both at and in the vicinity of the ferromagnetic resonant field in a hexagonal ferrite. The data obtained as part of this work show that the microwave field amplitude required to parametrically excite nonlinear spin wave amplitude growth in hexagonal ferrites is similar to polycrystalline cubic ferrites, which are currently in use in microwave devices. Follow-up measurements, motivated by this work, revealed that hcrit can be varied by manipulating the sample dimensions. The analyses performed here indicate that two-magnon scattering is likely not the dominant source of the large low-power microwave losses observed in these hexagonal ferrites; rather that these losses may be an intrinsic property of the material. The theoretical work performed here identified a sign problem with the anti-Larmor uniform mode complex damping terms in several past publications and provides an improved methodology of treating the uniform mode anti-Larmor complex frequency damping.Item Open Access Oblique pumping, resonance saturation, and spin wave instability processes in thin Permalloy films(Colorado State University. Libraries, 2008) Olson, Heidi M., author; Patton, Carl E., advisorThe study of nonlinear dynamics in metal films is of increasing importance as advancements are made in magnetic recording. In this dissertation, these interactions are examined by the study of first order spin wave instability (SWI) processes that occur for external static magnetic fields well below ferromagnetic resonance (FMR), and second order SWI processes that occur for static fields over the full FMR field range. This work is concerned specifically with the study of the high power resonance saturation and oblique pumping responses in thin Permalloy films, the microwave threshold amplitudes at which the instabilities occur, and the theoretical analysis of the relevant SWI processes. To greatly increase measurement accuracy and reduce measurement time, the high power FMR system has been modified and new calibration techniques implemented. The modifications to the system allow for fully automated and calibrated microwave threshold amplitude vs. static field measurements, termed butterfly curves. Resonance saturation butterfly curves have been measured for an in-plane field configuration for 35 - 123 nm thin Permalloy films. The butterfly curves show a jump on the low field side associated with a low field shift of the FMR profile and a foldover like asymmetry development. Apart from the jump, the second order Suhl SWI theory, suitably modified for thin films, provides good fits to the butterfly curve data through the use of constant spin wave relaxation rates that are on the same order as expected for intrinsic magnon-electron scattering processes. The FMR in-plane precession cone angles at threshold are small. Oblique pumping butterfly curves have been measured at different in-plane field configurations for 104 and 123 nm thin Permalloy films. The butterfly curves show thickness dependent high field cutoffs that agree with the field points at which the bottom of the spin wave band moves above one half the pump frequency. A combination of parallel and perpendicular first order SWI theory, suitably modified for thin films, shows good fits to the data except at low fields where the thin film approximation is not applicable. The damping trial functions used for the fits correspond to magnon-electron and three-magnon scattering processes.