Geometrically Constrained Skyrmions

Abstract

Skyrmions are chiral swirling magnetization structures with nanoscale size. These structures have attracted considerable attention due to their topological stability and promising applicability in nanodevices, since they can be displaced with spin-polarized currents. However, for the comprehensive implementation of skyrmions in devices, it is imperative to also attain control over their geometrical position. Here we show that, through thickness modulations introduced in the host material, it is possible to constrain three-dimensional skyrmions to desired regions. We investigate skyrmion structures in rectangular FeGe platelets with micromagnetic finite element simulations. First, we establish a phase diagram of the minimum-energy magnetic state as a function of the external magnetic field strength and the film thickness. Using this understanding, we generate preferential sites for skyrmions in the material by introducing dot-like “pockets” of reduced film thickness. We show that these pockets can serve as pinning centers for the skyrmions, thus making it possible to obtain a geometric control of the skyrmion position. This control allows for stabilization of skyrmions at positions and in configurations that they would otherwise not attain. Our findings may have implications for technological applications in which skyrmions are used as units of information that are displaced along racetrack-type shift register devices.

Robust and Programmable Logic-In-Memory Devices Exploiting Skyrmion Confinement and Channeling Using Local Energy Barriers

“…These skyrmions are resilient against external stray magnetic fields and possess velocities, which are much higher than their ferromagnetic counterparts, making them good candidates for elementary building blocks in storage and logic. In addition to using magnetic configurations with zero topological charge, SKHE can also be suppressed with different confinement techniques [24][25][26][27][28][29]. In particular, we have shown that skyrmion channels can be defined by a local modification of the magnetic properties using light ion irradiation.…”

Skyrmion pinning by disk-shaped defects

“…Their non-trivial topology, small size and ultralow driving force make them promising information carriers [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Similar to the importance of magnetic domain wall (DW) pinning [22] in DWbased devices, skyrmion pinning by disorders and intentionally created nano-structures is important in skyrmionics [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Skyrmion pinning in nano-structures with different exchange stiffness, or DMI strength, or magnetic anisotropy, or saturation magnetization has been investigated [10,[26][27][28][29].…”

“…Skyrmion pinning in nano-structures with different exchange stiffness, or DMI strength, or magnetic anisotropy, or saturation magnetization has been investigated [10,[26][27][28][29]. Skyrmion pinning by atomistic spin vacancies or geometrical constrains like film thickness modulations and semicircular notches at lateral boundaries has also been studied [29][30][31]. It was found [29] that pinning by a small structure can occur at or away from the center of a nano-structure.…”

Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He+-Ion Irradiation

“…Previous attempts to control the localization of skyrmions include structural patterning of the magnetic film with notches ,, and discs as well as the introduction of defects , and nanopockets to define positions for skyrmion nucleation. However, all of these methods include significant structural or even geometrical modifications of the magnetic racetrack and render an unhampered motion of the skyrmion after creation difficult.…”