This title appears in the Scientific Report :
2009
Please use the identifier:
http://hdl.handle.net/2128/14524 in citations.
Ultrafast vortex core dynamics investigated by finite-element micromagnetic simulations
Ultrafast vortex core dynamics investigated by finite-element micromagnetic simulations
The investigations carried out in this thesis concern the ultrafast dynamics of a fundamental micromagnetic conguration: the vortex. Over the past decade, a detailed understanding of the dynamic and static properties of such magnetic nanostructures has been achieved as a result of close interplay be...
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Personal Name(s): | Gliga, S. (Corresponding author) |
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Contributing Institute: |
Elektronische Eigenschaften; IFF-9 |
Imprint: |
Jülich
Forschngszentrum Jülich Gmbh Zentralbibliothek, Verlag
2009
|
Physical Description: |
VI, 144 S. |
Dissertation Note: |
Universität Duisburg |
ISBN: |
978-3-89336-660-6 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Grundlagen für zukünftige Informationstechnologien |
Series Title: |
Schriften des Forschungszentrums Jülich : Energie & Umwelt / Energy & Environment
79 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
The investigations carried out in this thesis concern the ultrafast dynamics of a fundamental micromagnetic conguration: the vortex. Over the past decade, a detailed understanding of the dynamic and static properties of such magnetic nanostructures has been achieved as a result of close interplay between experiments, theory and numeric simulations. Here, micromagnetic simulations were performed based on the nite-element method. The vortex structure arises in laterally-conned ferromagnets, in particular in thin-lm elements, and is characterized by an in-plane curling of the magnetic moments around a very stable and narrow core. In the present study, a novel process in micromagnetism was found: the ultrafast reversal of the vortex core. The possibility of easily switching the core orientation by means of short in-plane eld pulses is surprising in view of the very high stability of the core. Moreover, the simulations presented here showed that this reversal process unfolds on a time scale of only a few tens of picoseconds, which leads to the prediction of the fastest and most complex micromagnetic reversal process known to date. Indeed, the vortex core is not merely switched: it is destroyed and recreated in the immediate vicinity with an opposite direction. This is mediated by a rapid sequence of vortex-antivortex pair creation and annihilation subprocesses and results in a sudden burst-like emission of spin waves. Equally fascinating is the ultrafast dynamics of an isolated magnetic antivortex, the topological counterpart of the vortex. The simulations performed here showed that the static complementarity between vortices and antivortices is equally re ected in their ultrafast dynamics, which leads to the reversal of the antivortex core. A promising means for the control of the magnetization on the nanoscale consists in exploiting the spin-transfer torque eect. The study of the currentinduced dynamics of vortices showed that the core reversal can be triggered via two distinct routes. The rst is the resonant excitation by means of weak inplane alternating currents. In this case, the reversal occurs rather slowly, after several nanoseconds. The simulations demonstrated a second route, namely, that short unipolar electrical excitations applied in the plane of the sample can equally lead to the reversal of the core within only a few hundreds of picoseconds. Despite this dierence in switching times, the simulations showed that the micromagnetic details of the reversal are the same in both routes. By comparing these two switching paths, the origin of the core switch, i.e. the physical parameter responsible for the reversal, was identied. The analysis demonstrated the existence of an energy barrier, which corresponds to the energy required to create a new vortex-antivortex pair. In the simulations, such pairs were spontaneously produced once a specic local energy density was reached. This nding predicts that vortex-antivortex pairs can be created by applying a strong, localized magnetic eld. |