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Demonstration of bi-directional microwave-assisted magnetic reversal in synthetic ferrimagnets
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0002-9993-4748
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 14, 142408- p.Article in journal (Refereed) Published
Abstract [en]

We study spin dynamics in synthetic ferrimagnets, in which two dipole-coupled magnetic nanoparticles are different in thickness or biased asymmetrically with an external field. We observe a splitting of the optical spin-resonance for the two antiparallel ground states of the system and demonstrate how this splitting can be used to deterministically select a particular ground state. The demonstrated resonant switching is a fast and low-field way of controlling the magnetic state of nanodevices currently used in such large scale applications as magnetic random access memory.

Place, publisher, year, edition, pages
2013. Vol. 103, no 14, 142408- p.
Keyword [en]
Random-Access Memory, Giant Magnetoresistance, Tunnel-Junctions, Multilayers, Mram
National Category
Other Physics Topics
URN: urn:nbn:se:kth:diva-133647DOI: 10.1063/1.4824016ISI: 000325488500057ScopusID: 2-s2.0-84885578329OAI: diva2:663321

QC 20131111

Available from: 2013-11-11 Created: 2013-11-08 Last updated: 2016-05-24Bibliographically 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.Korenivski, Vladislav
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