Real-space observation of a two-dimensional skyrmion crystal

Magnetoelectric skyrmions Skyrmions are stable topological textures with particle-like properties, a mathematical concept originally developed to describe nuclear particles, but which in the past decade has found application at all scales from microscopic to cosmological. Skyrmions have proved particularly useful to describe novel spin configurations in magnets, and last year the presence of skyrmions in the magnetic compounds MnSi and Fe 1− x Co x Si was confirmed in neutron scattering experiments. Now Yu et al . present striking real-space images, using transmission electron microscopy, of a two-dimensional skyrmion lattice for the latter compound, in the form of a hexagonal arrangement of swirling spin structures. The lattice is shown to be stable for a wide range of temperatures and magnetic fields. The authors speculate that the observed nanometre-scale spin topology may lead to interesting new magnetoelectric effects. Skyrmions are stable topological textures with particle-like properties — a mathematical concept that was originally used to describe nuclear particles but has since turned up at all scales. Last year, the presence of skyrmions in the magnetic compounds MnSi and Fe 1−x Co x Si was confirmed with neutron-scattering experiments. Here, real-space images are presented of a two-dimensional skyrmion lattice in a thin film of the latter compound. The observed nanometre-scale spin topology might reveal new magneto-transport effects. Crystal order is not restricted to the periodic atomic array, but can also be found in electronic systems such as the Wigner crystal 1 or in the form of orbital order 2 , stripe order 3 and magnetic order. In the case of magnetic order, spins align parallel to each other in ferromagnets and antiparallel in antiferromagnets. In other, less conventional, cases, spins can sometimes form highly nontrivial structures called spin textures 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 . Among them is the unusual, topologically stable skyrmion spin texture, in which the spins point in all the directions wrapping a sphere 4 , 5 , 6 , 7 . The skyrmion configuration in a magnetic solid is anticipated to produce unconventional spin–electronic phenomena such as the topological Hall effect 24 , 25 , 26 . The crystallization of skyrmions as driven by thermal fluctuations has recently been confirmed in a narrow region of the temperature/magnetic field ( T – B ) phase diagram in neutron