Skyrmionics—Computing and memory technologies based on topological excitations in magnets

Abstract

Solitonic magnetic excitations such as domain walls and, specifically, skyrmionics enable the possibility of compact, high density, ultrafast, all-electronic, low-energy devices, which is the basis for the emerging area of skyrmionics. The topological winding of skyrmion spins affects their overall lifetime, energetics, and dynamical behavior. In this Perspective, we discuss skyrmionics in the context of the present-day solid-state memory landscape and show how their size, stability, and mobility can be controlled by material engineering, as well as how they can be nucleated and detected. Ferrimagnets near their compensation points are promising candidates for this application, leading to a detailed exploration of amorphous CoGd as well as the study of emergent materials such as Mn4N and inverse Heusler alloys. Along with material properties, geometrical parameters such as film thickness, defect density, and notches can be used to tune skyrmion properties, such as their size and stability. Topology, however, can be a double-edged sword, especially for isolated metastable skyrmions, as it brings stability at the cost of additional damping and deflective Magnus forces compared to domain walls. Skyrmion deformation in response to forces also makes them intrinsically slower than domain walls. We explore potential analog applications of skyrmions, including temporal memory at low density—one skyrmion per racetrack—that capitalizes on their near ballistic current–velocity relation to map temporal data to spatial data and decorrelators for stochastic computing at a higher density that capitalizes on their interactions. We summarize the main challenges of achieving a skyrmionics technology, including maintaining positional stability with very high accuracy and electrical readout, especially for small ferrimagnetic skyrmions, deterministic nucleation, and annihilation and overall integration with digital circuits with the associated circuit overhead.

Size-dependent mobility of skyrmions beyond pinning in ferrimagnetic GdCo thin films

“…Since n corresponds to the skyrmion topological number, it is independent of the skyrmion size (n " ˘4π depending on the skyrmion core polarity). The integral d is similar to the micromagnetic exchange integral [31,42], and…”

Mechanism of Topology Change of Flat Magnetic Structures

“…[ 1 , 2 ]. The most promising in this respect are the devices based on magnetic films, in which vortex-like magnetic inhomogeneities can originate (for example, magnetic vortices, skyrmions, bimerons, and magnetic bubbles [ 3 , 4 , 5 , 6 , 7 , 8 ]). There are certain difficulties, however, which stand in the way of creating such devices.…”

Structural transition of skyrmion quasiparticles under compression

“…They are usually very rigid objects and can interact with each other effectively through the short-range skyrmion-skyrmion interaction and long-range dipolar interaction [3,[35][36][37][38][39]. As the skyrmion carries a nonzero integer topological charge, its dynamics in a flat landscape are subject to both external driving forces and its topological nature [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Such a feature may lead to some unique dynamics compared to common particles.…”