Role of impurity clusters for the current-driven motion of magnetic skyrmions

Abstract

We study how impurities influence the current-induced dynamics of magnetic skyrmions moving in a racetrack geometry. For this, we solve numerically the generalized Landau-Lifshitz-Gilbert equation extended by the current-induced spin transfer torque. In particular, we investigate two classes of impurities, nonconducting and magnetic impurities. The first are magnetically rigid objects and yield to an inhomogeneous current density over the racetrack, which we determine separately by solving the fundamental electrostatic equations. In contrast, magnetic impurities leave the applied current density homogeneous throughout the stripe. Depending on the parameters, we observe four different scenarios of skyrmion motions in the presence of disorder, the skyrmion decay, the pinning, the creation of additional skyrmions, and ordinary skyrmion passage. We calculate and discuss phase diagrams in the dependence of the impurity concentration and radii of the impurities.

Skyrmion bound state and dynamics in an antiferromagnetic bilayer racetrack

“…where i and j sum over the horizontal and vertical directions of m-layer, and η k,m = S 2k,m − S 2k+1,m 2 is the Néel vector. Thereby, the position of the skyrmion center of mass in the m-layer, r sk,m = (x sk,m , y sk,m ), is given by [59,61]:…”

“…The investigation of disordered systems plays an essential role in skyrmion dynamics because these imperfections can change drastically its movement. For example, magnetic defects can alter the SHE angle expressively in FM media [61]. Additionally, there are some theoretical and experimental shreds of evidence that skyrmions can be created, annihilated, and pinned by magnetic impurities [18,28,61,[64][65][66].…”

“…For example, magnetic defects can alter the SHE angle expressively in FM media [61]. Additionally, there are some theoretical and experimental shreds of evidence that skyrmions can be created, annihilated, and pinned by magnetic impurities [18,28,61,[64][65][66]. In this way, after analyzing the dynamical properties of coupled skyrmions in a bilayer without impurities or defects, we study the dynamics of the SBS in a disordered system.…”

Micromagnetic manipulation and spin excitation of skyrmionic structures

“…The disorder in the above two works was simulated as a granular structure, in which the local anisotropy varied randomly from grain to grain. In 2021, Stier et al [122] investigated two classes of impurities: nonconducting and magnetic impurities. The first were magnetically rigid objects which yield to an inhomogeneous current density while the second leave the current density homogeneous throughout the nanotrack.…”

Creating arbitrary sequences of mobile magnetic skyrmions and antiskyrmions

“…Particularly for the use of racetrack devices, SKs are typically moved by electrical currents [24] while also magnetic fields [25,26] or a edgeinduced pushing [15] may be used. Notable obstacles for precise SK dynamics in terms of technical usability are the topological SK Hall effect [27][28][29] or material impurities [30,31]. It is also important to spatially separate the logical bits within a memory device which lead to the proposal of two-lane racetracks [3,29,32] or the simultaneous use of two different data carriers as domain walls and SKs [15].…”