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Soliton-pair dynamics in patterned ferromagnetic ellipses


Confinement alters the energy landscape of nanoscale magnets, leading to the appearance of unusual magnetic states, such as vortices, for example. Many basic questions concerning dynamical and interaction effects remain unanswered, and nanomagnets are convenient model systems for studying these fundamental physical phenomena. A single vortex in restricted geometry, also known as a non-localized soliton, possesses a characteristic translational excitation mode that corresponds to spiral-like motion of the vortex core around its equilibrium position. Here, we investigate, by a microwave reflection technique, the dynamics of magnetic soliton pairs confined in lithographically defined, ferromagnetic Permalloy ellipses. Through a comparison with micromagnetic simulations, the observed strong resonances in the subgigahertz frequency range can be assigned to the translational modes of vortex pairs with parallel or antiparallel core polarizations. Vortex polarizations play a negligible role in the static interaction between two vortices, but their effect dominates the dynamics.

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Figure 1: MFM and simulations of the two-vortex remanent states.
Figure 2: Experimentally measured vortex-pair resonance frequencies.
Figure 3: Diagrams of the magnetization configurations and dynamic modes for two magnetic vortices confined in an ellipse.
Figure 4: Micromagnetic simulation results showing the excitation frequencies as a function of H.


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We thank Y. Otani and J. Pearson for stimulating discussions and R. Divan for lithography support. This work was supported by the US Department of Energy, Basic Energy Sciences, Material Sciences under Contract No. W-31-109-ENG-38. K.S.B. thanks NSERC of Canada for a fellowship. P.E.R. acknowledges support from the Swedish Research Council and Swedish Foundation for Strategic Research.

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Correspondence to Valentyn Novosad.

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Buchanan, K., Roy, P., Grimsditch, M. et al. Soliton-pair dynamics in patterned ferromagnetic ellipses. Nature Phys 1, 172–176 (2005).

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