Skyrmion

A skyrmion is a topologically protected spin structure in which the local magnetization forms a swirling texture that wraps the unit sphere once. In condensed matter physics, magnetic skyrmions are nanoscale spin textures characterized by an integer topological charge, often denoted Nsk = ±1. This charge can be expressed as Nsk = (1/4π) ∫ m · (∂x m × ∂y m) d^2r, where m is the unit magnetization field. The nontrivial topology makes skyrmions robust against moderate perturbations and defines their emergent electrodynamic properties.

Skyrmions arise in magnetic materials that favor twists in the spin texture, most notably in systems with strong Dzyaloshinskii–Moriya interaction (DMI). In bulk chiral magnets, or in thin-film heterostructures with interfacial DMI, competition among exchange interaction, DMI, magnetic anisotropy, and the Zeeman energy from an applied magnetic field stabilizes skyrmions. They can exist as isolated particles or form ordered lattices known as skyrmion crystals. Observations span bulk materials such as MnSi and FeGe and thin-film multilayers engineered to sustain DMI.

In dynamics, skyrmions can be moved by electric currents through spin-transfer or spin-orbit torques with relatively low current densities. Their topology also leads to a transverse, or Hall, component in their motion, called the skyrmion Hall effect. Imaging techniques such as Lorentz transmission electron microscopy, spin-polarized scanning probe methods, and X-ray magnetic imaging have revealed their structure and behavior.

Applications are under exploration for high-density magnetic storage, racetrack memory concepts, and neuromorphic or unconventional computing. Ongoing research seeks reliable room-temperature stabilization, controlled creation and annihilation, and integration into scalable devices.