Magnetoelectric skyrmions in multiferroics

Skyrmion is a topologically stable particle-like object originally proposed by field theory, which has recently been identified in chiral-lattice magnets as vortex-like swirling spin texture of typical size ranging from 5 nm to 100 nm[1,2] . In metallic system, skyrmions can be moved by electric current through the spin-transfer torque[3] . Because of its electric controllability, nanometric scale, and particle-like nature, skyrmion is now rapidly attracting attention as a promising building block for novel spintronic device like high density magnetic storage[4] . However, such current-driven approach inevitably involves joule heat loss, and the previous observation of skyrmions has been limited to specific metallic alloys with chiral B20 structure . Based on the assumption that the chiral symmetry of underlying crystal lattice and associated Dzyaloshinskii-Moriya interaction plays a crucial role for the stabilization of skyrmion spin texture, we have recently discovered the emergence of skyrmions in a chiral-lattice insulator Cu₂OSeO₃ by performing the Lorentz transmission electron microscopy and small angle neutron scattering[5,6] . Through the detailed dielectric and magnetic measurements, we proved that the skyrmion spin texture in insulator can magnetically induce electric polarization via the relativistic spin-orbit interaction[7] . Such a coupling between skyrmion spin texture and electric dipole strongly suggests that skyrmions in insulators can be manipulated by external electric field, which has later been confirmed by the experiments of small angle neutron scattering[8] and magnetic resonance[9] . Since this approach is free from the Joule heat loss compared to the current-driven method in the metallic system, our present finding of magnetoelectric skyrmions in insulators can be considered as a key milestone for the development of next generation of ultra-high-density magnetic storage device with extremely low energy consumption .