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Static and dynamic properties of vortex pairs in asymmetric nanomagnets
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0002-9993-4748
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2016 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, no 5, 056406Article in journal (Refereed) PublishedText
Abstract [en]

Stacked spin-vortex pairs in magnetic multilayered nanopillars, with vertical separation between the vortices small compared to the vortex core size and pure magnetostatic coupling, exhibit spin dynamics absent in individual vortices. This dynamics is nonlinear and is due to the strong direct core-core coupling in the system, dominating energetically for small-signal excitation. We observe and explain the appearance of spin resonance modes, forbidden within linear dynamics, and discuss how they depend on the magnetic and morphological asymmetries in the samples.

Place, publisher, year, edition, pages
American Institute of Physics Inc. , 2016. Vol. 6, no 5, 056406
Keyword [en]
Spin dynamics, Dynamic property, Linear dynamics, Magneto-static couplings, Multi-layered, Signal excitation, Spin resonance, Vertical separation, Vortex cores, Vortex flow
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-186979DOI: 10.1063/1.4944515ISI: 000377962500262ScopusID: 2-s2.0-84961589525OAI: diva2:929909
13th Joint Magnetism and Magnetic Materials (MMM)/Intermag Conference, Jan 11-15, 2016, San Diego, CA
Swedish Research Council, 2014-4548

QC 20160520

Available from: 2016-05-20 Created: 2016-05-16 Last updated: 2016-07-18Bibliographically approved
In thesis
1. Static and dynamic properties of uniform- and vortex-states in synthetic nanomagnets
Open this publication in new window or tab >>Static and dynamic properties of uniform- and vortex-states in synthetic nanomagnets
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Synthetic antiferromagnets (SAFs) consist of two thin ferromagnetic particles separated by a thin nonmagnetic spacer. The magnetic moments of the two particles couple antiparallel via dipolar interactions, with the interlayer exchange interaction suppressed by a suitable choice of the spacer material. The SAF system studied in this thesis contains thin elliptical-in-the-plane permalloy particles magnetized uniformly and mutually antiparallel in the ground state. A SAF can also exhibit long-lived metastable nonuniform magnetization states, such as spin-vortex pairs. The thesis explores hysteresis and spin dynamics in: (i) uniformly magnetized SAFs and (ii) SAFs in the vortex-pair state.

The uniformly magnetized antiparallel ground state of a symmetrical SAF, having identical ferromagnetic particles, is double  degenerate. The resonance modes are in-phase (acoustical) and out-of-phase (optical) oscillations of the magnetic moments. Asymmetry between the two magnetic layers is shown to lift the degeneracy of the antiparallel ground state, which in the static regime results in unequal stability of the two states. In the dynamic regime, the asymmetries are shown to result in a splitting of the resonance frequency of the new non-degenerate ground states. The resulting resonant-mode splitting can be used to selectively switch between the antiparallel ground states by resonant microwave or thermal activation of the system.

The static and dynamic properties of the vortex pairs in SAFs were found to be strongly dependent on the relative orientation of the vortex chiralities and vortex-core polarizations in the two ferromagnetic particles of the SAF. For parallel core polarizations, a strong monopole-like core-core interaction is found to dominate the magnetic properties of the system, increasing the characteristic resonance frequency by an order of magnitude.  Analytical theory and numerical micromagnetic simulations are used to explain the measured responses.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. 74 p.
National Category
Condensed Matter Physics
Research subject
urn:nbn:se:kth:diva-187473 (URN)978-91-7729-018-6 (ISBN)
Public defence
2016-06-15, FB54, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Swedish Research Council, 2014-4548Stiftelsen Olle Engkvist Byggmästare, 2014-STE

QC 20160524

Available from: 2016-05-24 Created: 2016-05-24 Last updated: 2016-05-25Bibliographically approved

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Koop, Björn C.Descamps, ThomasKorenivski, Vladislav
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