Magnetic Skyrmions
topological spin textures · DM interaction · winding number
Physics: Magnetic skyrmion: topological spin texture where the spin rotates continuously from ↑ at center to ↓ at the edge, wrapping the unit sphere once. Topological charge (winding number) Q = −(1/4π)∫n·(∂_x n × ∂_y n) dA = ±1; cannot be unwound without breaking the spin texture. Stabilized by Dzyaloshinskii-Moriya interaction (DMI): H_DM = D·(Sᵢ × Sⱼ), which requires broken inversion symmetry. Skyrmion size 5–100 nm; can be driven at v ~ 1000 m/s with small currents. Discovered in MnSi (2009). Candidate for high-density magnetic memory (dense, small, stable).