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Magnetic-field tunability of the vortex translational mode in micron-sized permalloy ellipses: Experiment and micromagnetic modeling
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 6, 064404- p.Article in journal (Refereed) Published
Abstract [en]

A magnetic vortex confined in a magnetically soft ferromagnet with micron-sized dimensions possesses a characteristic dynamic excitation known as a translational mode that corresponds to spiral-like precession of the vortex core around its equilibrium position. We report micromagnetic modeling and experimental detection using a microwave reflection technique of the magnetic field tunability of this mode in 40 nm thick, 3x1.5 mu m(2) and 2x1 mu m(2) permalloy ellipses. At remanence the translational modes are detected at 77 and 118 MHz. The frequency shows a strongly anisotropic dependence on magnetic field applied in the plane of the ellipse. The frequencies more than double when a static field is applied along the hard (short) axis, whereas they are almost field-independent when the field is aligned with the easy (long) axis. Micromagnetic calculations reveal that the observed behavior is governed by the shape of the energy potential well that is influenced mainly by magnetostatic and Zeeman energies.

Place, publisher, year, edition, pages
2006. Vol. 74, no 6, 064404- p.
National Category
Physical Sciences Engineering and Technology
URN: urn:nbn:se:uu:diva-94727DOI: 10.1103/PhysRevB.74.064404ISI: 000240238500040OAI: oai:DiVA.org:uu-94727DiVA: diva2:168687
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2016-07-12Bibliographically approved
In thesis
1. On Some Properties and Applications of Patterned Ferromagnetic Thin Films
Open this publication in new window or tab >>On Some Properties and Applications of Patterned Ferromagnetic Thin Films
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A microwave reflection method has been used to measure the spin excitations corresponding to the translational mode of magnetic vortices in samples containing either one or two vortices. Experimental findings are complemented by micromagnetic simulations.

One-vortex systems are investigated in micron-sized circular and elliptical cylinders. For ellipses, the resonance frequency can effectively be tuned by applying static magnetic fields and the field dependence of the frequency is significant for fields applied along the short axes but negligible when applied along the long axes of the ellipses. This is contrary to the circular case, where virtually no field dependence was found. This can be understood by considering the shape of the vortex potential well. Further, it is found that the resonance frequency is independent on the direction of the excitation field for the one-vortex systems.

Ellipses containing two interacting vortices are also investigated. It is shown that the relative vortex core polarizations dominate the vortex translational mode and cause, in the case of opposite polarizations, a dependence on the excitation field direction. For parallel core polarizations, no dependence on the excitation field direction is found. The dependence of the resonance frequencies on applied static fields along the long and short axes are also experimentally mapped out and compared with micromagnetic simulations, where the possible eigenmodes are determined.

Another section of the thesis introduces the dawning of a device based on patterned magnetic elliptical elements for the manipulation and movement of magnetic particles on a surface. The controlled movement and separation of individual particles are successfully demonstrated.

Contributions to micromagnetic standard problems and simulations on magnetization switching in nanoscale particles have also been performed. The standard problems highlight some important aspects of choosing the discretization cell sizes and the finite temperature simulations show that thermal fluctuations can alter the magnetization reversal paths.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 93 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 204
Materials science, micromagnetics, vortex, spin dynamics, domains, MFM, microwave, patterned, permalloy, Materialvetenskap
National Category
Materials Engineering
urn:nbn:se:uu:diva-7091 (URN)91-554-6624-9 (ISBN)
Public defence
2006-09-28, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:00 (English)
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2009-03-27Bibliographically approved

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