Energetic Transitions of Magnetic Vortices

• Author / Creator

  Burgess, Jacob A.J.

• 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.

• Subjects / Keywords

  • Time Resolved STM
  • Scanning Tunneling Microscopy
  • Deformable Vortex Pinning Model
  • Micromagnetics
  • Magnetic Vortex
  • Metallic Glass
  • Spin Polarized STM
  • Magneto-optical Kerr Effect
  • Magnetic Pinning
  • Vortex Core Pinning
  • Magnetism
  • Torsional Magnetometry

• Graduation date

  Spring 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3V091

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.