Electric-current-driven vortex-core reversal in soft magnetic nanodots

Kim, Sang‐Koog; Choi, Youn-Seok; Lee, Ki-Suk; Guslienko, K. Yu.; Jeong, Dong Seop

doi:10.1063/1.2773748

Cited by 94 publications

(80 citation statements)

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“…The final state is then a CCW circular vortex with negative polarity (see Supplemental Material MOVIE 4 for an example of the switching process at J MTJ =5MA/cm 2 ). This switching process is different from previous mechanisms reported in literature involving edge solitons [40], gyrotropic motion [41], or vortexantivortex pairs [42]. , where K B is the Boltzmann constant, ΔV is the volume of the computational cubic cell, Δt is the simulation time step, T is the temperature of the sample, and χ is a three-dimensional white Gaussian noise with zero mean and unit variance, and it is uncorrelated for each computational cell [5,6].…”

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confidence: 44%

Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque

et al. 2016

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Solitons are very promising for the design of the next generation of ultralow power devices for storage and computation. The key ingredient to achieve this goal is the fundamental understanding of their stabilization and manipulation. Here, we show how the interfacial Dzyaloshinskii-Moriya Interaction (i-DMI) is able to lift the energy degeneracy of a magnetic vortex state by stabilizing a topological soliton with radial chirality, hereafter called radial vortex. It has a non-integer skyrmion number S (0.5<|S|<1) due to both the vortex core polarity and the magnetization tilting induced by the i-DMI boundary conditions. Micromagnetic simulations predict that a magnetoresistive memory based on the radial vortex state in both free and polarizer layers can be efficiently switched by a threshold current density smaller than 10 6 A/cm 2 . The switching processes occur via the nucleation of topologically connected vortices and vortexantivortex pairs, followed by spin-wave emissions due to vortex-antivortex annihilations. 2Magnetic solitons, such as domain walls (DWs) [1,2,3,4], vortices [5,6,7,8,9,10,11] and skyrmions [12,13,14,15,16,17] From a fundamental point of view, the stabilization of a radial vortex gives rise to the possibility to create current densities with radial polarization for particle-trapping applications, such as skyrmion [22], analogously to what radially polarized beams can do in many optical systems [23].In order to show the main features and the possible applications of the radial vortex, extensive micromagnetic simulations have been performed. The first part of this letter focuses on the fundamental properties of the radial vortex, in terms of stability as a function of the i-DMI, 3 topology, nucleation as well as response to an in-plane field. The second part is dedicated to the analysis of the switching process of the radial vortex, underlining the differences with the circular vortex.We consider a CoFeB disk having a diameter d=250nm and a thickness t=1.0nm to have an in-plane easy axis at zero external field. To add the i-DMI, we consider the CoFeB coupled with a Pt (heavy metal) layer as already experimentally observed [24]. The study is carried out by means of a state-of-the-art micromagnetic solver which numerically integrates the Landau-Lifshitz-Gilbert (LLG) equation [25,26,27], that includes the i-DMI contribution Fig.4(a)). An H ext =5.0mT yields a uniform magnetic state. Fig.4(b) shows the results for the circular vortex (|D|=0.0mJ/m 2 ). The displacement occurs along the direction perpendicular to the external field (insets Fig.4(b)) [7,32,33,34,35]. Together with the qualitatively different vortex core shift, the field value that leads to the radial vortex core expulsion is twice the one of the circular vortex. This is ascribed to the i-DMI and, in particular, to its boundary conditions, in fact, the expulsion field increases as a function of |D|. The key reason for that is the need of a larger field to align the out-of-plane tilted spins at the sample edges 5 perpendicu...

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Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque

et al. 2016

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“…[9][10][11][12][13][14][15][16][17][18][19][20] For instance, the current-driven vortex gyrotropic oscillation [9][10][11][12][13] and vortex core ͑VC͒ M switching [14][15][16][17][18][19][20] in confined magnetic systems have been observed both experimentally [9][10][11]13,14 and numerically. 12,[15][16][17][18][19][20] Despite the several studies conducted on the STT effect on such vortex excitations, quantitative understanding of the Oersted field ͑OH͒ effect of the spinpolarized currents has been lacking, even though this type of field has been reported to make sizable contributions to M reversals 5,21,22 and VC oscillations. 9,10,13 In this letter, we report the observation of sizable shifts in the intrinsic eigenfrequency D = ͑1 / 2 ͒ , of vortex gyrotropic motions in a laterally confined thin-film nanodot.…”

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confidence: 99%

Understanding eigenfrequency shifts observed in vortex gyrotropic motions in a magnetic nanodot driven by spin-polarized out-of-plane dc current

Choi

Kim

Lee

2008

Applied Physics Letters

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“…The velocities of the defects do not typically exceed the core switching velocity of permalloy (340 ± 20 m/s) [37]. However, sometimes an exception occurs in antiparallel vortex-antivortex annihilations.…”

Section: B Defect Dynamics During Relaxationmentioning

confidence: 99%

Coarsening dynamics of topological defects in thin permalloy films

Rissanen

Laurson

2016

Phys. Rev. B

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We study the dynamics of topological defects in the magnetic texture of rectangular permalloy thin-film elements during relaxation from random magnetization initial states. Our full micromagnetic simulations reveal complex defect dynamics during relaxation towards the stable Landau closure domain pattern, manifested as temporal power-law decay, with a system-size-dependent cutoff time, of various quantities. These include the energy density of the system and the number densities of the different kinds of topological defects present in the system. The related power-law exponents assume nontrivial values and are found to be different for the different defect types. The exponents are robust against a moderate increase in the Gilbert damping constant and introduction of quenched structural disorder. We discuss details of the processes allowed by conservation of the winding number of the defects, underlying their complex coarsening dynamics.

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Electric-current-driven vortex-core reversal in soft magnetic nanodots

Abstract: Articles you may be interested inRadial-spin-wave-mode-assisted vortex-core magnetization reversals Appl. Phys. Lett. 100, 172413 (2012) Effect of the classical ampere field in micromagnetic computations of spin polarized current-driven magnetization processes

Cited by 94 publications

References 27 publications

Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque

Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque

Understanding eigenfrequency shifts observed in vortex gyrotropic motions in a magnetic nanodot driven by spin-polarized out-of-plane dc current

Coarsening dynamics of topological defects in thin permalloy films

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