Edge-Soliton-Mediated Vortex-Core Reversal Dynamics

Ki-Suk Lee, Myoung-Woo Yoo, Youn-Seok Choi, and Sang-Koog Kim

Phys. Rev. Lett. 106, 147201 – Published 4 April 2011

Abstract

We report an additional reversal mechanism of magnetic vortex cores in nanodot elements driven by currents flowing perpendicular to the sample plane, occurring via dynamic transformations between two coupled edge solitons and bulk vortex solitons. This mechanism differs completely from the well-known switching process mediated by the creation and annihilation of vortex-antivortex pairs in terms of the associated topological solitons, energies, and spin-wave emissions. Strongly localized out-of-plane gyrotropic fields induced by the fast motion of the coupled edge solitons enable a magnetization dip that plays a crucial role in the formation of the reversed core magnetization. This work provides a deeper physical insight into the dynamic transformations of magnetic topological solitons in nanoelements.

Received 29 November 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.147201

Authors & Affiliations

Ki-Suk Lee, Myoung-Woo Yoo, Youn-Seok Choi, and Sang-Koog Kim^*

National Creative Research Initiative Center for Spin Dynamics & Spin-Wave Devices, Nanospinics Laboratory, Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea

^*To whom all correspondence should be addressed. sangkoog@snu.ac.kr

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Vol. 106, Iss. 14 — 8 April 2011

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Images

Figure 1
Schematic illustration of model system. (a) Free-standing Py disk of indicated dimensions. (b) Spatial distribution of strength of OHs induced by current flow of the indicated density $j_{0}$ . The wide arrow and color-coded bar indicate the in-plane rotation sense (here, CCW for $i_{p} = + 1$ ) and the strength, respectively.Reuse & Permissions
Figure 2
Representative distinct vortex excitations driven by out-of-plane dc currents in different regions of $j_{0}$ . For each region we chose $j_{0} = 1.5$ (a), 2.0 (b), and $3.0 \times 10^{6} A / {cm}^{2}$ (c), respectively. Top of each $j_{0}$ : snapshot perspective images of temporal evolution of vortex dynamics. The height of the surface indicates the out-of-plane components of the local magnetizations, and the streamlines with arrows indicate the in-plane components. Bottom of each: trajectories of in-plane motions of upward (red) VC and its reversed downward (blue) core, or coupled edge solitons (purple).Reuse & Permissions
Figure 3
Comparison of two different dynamic behaviors associated with two coupled edge solitons: (a) in-plane persistent rotation of two edge solitons at disk boundary and (b) transformation to VC of reversed orientation. The color coding indicates the out-of-plane components of the local magnetizations, while the streamlines with arrows indicate the in-plane components. The dotted red arrows represent the directions of the motion of the coupled edge solitons. The right column shows the exchange ( $E_{ex}$ ), demagnetization ( $E_{de}$ ) energies and their sum ( $E_{tot}$ ), and velocity ( $υ$ ) variations, where the vertical lines are drawn at the indicated times shown in the corresponding snapshot images (left). The orange horizontal lines represent the value of $υ = 350 m / s$ .Reuse & Permissions
Figure 4
(a) Spatial distributions of magnetization deformation $m_{z}$ (left) and normal component of associated out-of-plane gyrotropic field $h_{z}$ (right), for indicated $j_{0}$ values, as indicated by corresponding color codes. The streamlines with arrows indicate the in-plane local magnetizations. (b) Plots of magnetization dip $m_{z, dip} = M_{z, dip} / M_{s}$ and minima of local $h_{z}$ as functions of $j_{0}$ along with the velocity of motion of coupled edge solitons and associated energy variation. The vertical dotted line indicates the boundary above which value VC reversals occur through the two coupled edge solitons. Above $j_{0}$ marked by the dotted vertical line, each value was estimated at the time when the reversed VC starts to gyrate with the characteristic damping motion.Reuse & Permissions

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