Date of Award
Open Access Thesis
Paul G. Huray
Ultrafast time-domain measurements are made on collections of Fe3O4 magnetic nanoparticles using an inductive measurement technique. The 10nm particles are placed directly on a coplanar waveguide (CPW) situated in an adjustable external magnetic bias field. A fast-rising step current in the CPW quickly changes the orientation of the local magnetic field causing the magnetization to align in the new field configuration. This rapidly changing magnetization induces a voltage in the CPW that is detected by a sampling oscilloscope. Magnetization dynamics predicted by the Landau-Lifshitz (LL) equation including magnetic precession and phenomenological damping are observed. The time-domain data are fitted to damped sinusoidal solutions of the LL equation. Frequency analysis is done using a Fast Fourier transform on the time-domain data. Two prominent frequency peaks are observed centering around 1.3 GHz and 3.5 GHz. The frequency data are then fitted to the general Kittel equation for ferromagnetic resonance. The demagnetization factors are found to be those of very nearly spherical objects, rather than the collective shape of the overall sample. Fitted gfactors for samples are found to be in excellent agreement with previously published values. Low frequency damping generally decreases with increasing bias field, a result in qualitative agreement with published pulsed inductive detection on magnetic films. High frequency damping reaches a minimum at sample-dependent field values.
Egenriether, B.(2016). Time-Domain Measurement Of Ultrafast Magnetization Dynamics In Magnetic Nanoparticles. (Master's thesis). Retrieved from https://scholarcommons.sc.edu/etd/3439