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Energetic Transitions of Magnetic Vortices Open Access


Other title
Torsional Magnetometry
Magnetic Pinning
Scanning Tunneling Microscopy
Spin Polarized STM
Magneto-optical Kerr Effect
Vortex Core Pinning
Magnetic Vortex
Deformable Vortex Pinning Model
Time Resolved STM
Metallic Glass
Type of item
Degree grantor
University of Alberta
Author or creator
Burgess, Jacob A.J.
Supervisor and department
Freeman, Mark R. (Department of Physics)
Examining committee member and department
Hallin, Aksel (Department of Physics)
Mar, Arthur (Department of Chemistry)
Freeman, Mark R. (Department of Physics)
Heinrich, Bret (Simon Fraser University, Department of Physics)
Wolkow, Robert (Department of Physics)
Czarnecki, Andrzej (Department of Physics)
Department of Physics

Date accepted
Graduation date
Doctor of Philosophy
Degree level
The vortex state in a magnetic disk contains a zero-dimensional domain wall, and consequently, is a system of interest for the study of fundamental physics. In particular, the disk geometry presents a prototypical system to study the properties of vortex states and to construct proof-of-concept magnetic logic devices. Here, work was performed to elevate the understanding of this system so that device development and experiments may be performed in a truly quantitative fashion. In order to achieve this, hysteretic transitions of the vortex state in thin-film magnetic disks were studied using a variety of techniques. The annihilation transition and its statistics arising from thermal dynamics were studied using a novel tool, AC magneto-optical Kerr effect susceptometry, that permits rapid acquisition of transition statistics. Much smaller hysteretic transitions were studied using extremely sensitive torsional magnetometry. Strong interactions between the core of the vortex and inhomogeneities in the thin-film were studied in 1D and 2D. The bistable states participating in hysteresis were found to exhibit low speed stochastic dynamics that allowed quantitative analysis of transition barriers. To aid in this work an improved analytical model describing the evolution of the vortex state with applied field was developed. In particular this model was demonstrated to be capable of correctly accounting for both the non-monotonic evolution of the magnetization and the vortex core position of the vortex state under a changing magnetic field in the presence of a pinning site. The combination of the model with the torsional magnetometer creates a powerful scanning vortex probe microscope, capable of imaging the energy landscape of the disk with a high spatial resolution. Concurrently, a time-resolved STM equipped with spin polarized tips was successfully constructed, and applied to study in situ fabricated patterned magnetic disks. This attempt to observe magneto-dynamics on an unprecedented combination of spatial and temporal scales has not yet provided results, as magnetic contrast remains elusive. In developing novel high speed STM samples, cluster dynamics were discovered and studied in a metallic glass. In addition to equilibrium dynamics, the formation of a surface state of large clusters was directly observed as the film aged.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
J. A. J. Burgess, et al., Science 339, 1051 (2013).J. A. J. Burgess, J. E. Losby, M. R. Freeman, arXiv:1208.3797 [cond-mat.mes-hall] (2012).J. A. J. Burgess, et al., Physical Review B 82, 144403 (2010).

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File title: Introduction to Modern Magnetism
File title: Energetic Transitions of Magnetic Vortices, Ph. D. Thesis
File author: Jacob A. J. Burgess
Page count: 283
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