[abstract] In the process of nucleation, the decay of a metastable state is initiated by the formation of a spatially localised region called a nucleus of critical size. In many realistic situations nucleation is initiated at an impurity or defect; such as a dust particle, an irregularity in a sample, or a crack in the wall of a container. The aim of this thesis is to identify and understand the fundamental changes different types of defect make to nucleation by studying a one-dimensional continuum model used to describe solitons. A well established theory due to Langer is extended to calculate the rate of decay of a metastable state due to the nucleation of solitons at defects. Results are used to find the rate of thermally activated magnetisation reversal for a ferromagnetic nanowire with defects in the uniaxial anisotropy. Defects which are narrower than the soliton width (point-like defects) and wider than the soliton width (step defects) are both modelled. An attractive defect breaks the translational symmetry of a soliton and leads to pinning. The pinning of solitons is found to reduce the activation energy required for nucleation, reduce the critical field above which a metastable state becomes unstable, alter the mechanism by which a metastable state decays, and modify the prefactor for the rate of decay. Changes to the prefactor are interpreted in terms of entropy and the dynamics of metastable decay when a defect is present.
| Identifer | oai:union.ndltd.org:ADTP/221358 |
| Creators | Loxley, Peter |
| Publisher | University of Western Australia. School of Physics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Peter Loxley, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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