Skyrmion domains in Cu2OSeO3: Short-Range Order and Domain Wall Formation

Cu$_2$OSeO$_3$ is a chiral ferrimagnetic insulator carrying a long-range order magnetic skyrmion phase. Here, we report a short-range ordered equilibrium skyrmion state on the surface of Cu$_2$OSeO$_3$ single crystal, studied by resonant soft x-ray scattering. Soft x-ray scattering at the $L_{2,3}$ edge of $3d$ compounds is an ideal tool to probe the magnetic order, and is only sensitive to ~60-70 unit cells in depth of Cu$_2$OSeO$_3$. Our results show that under the arbitrary magnetic field directions that deviate from the cubic main axes, the six-fold-symmetric skyrmion order breaks into domains, and the initial, anisotropy-governed pinning of propagation directions is completely unwound. We show that uniform $360^\circ$ Bloch domain walls form between the skyrmion domains. Our findings provide a new way to manipulate and engineer the skyrmion state locally, or even individually, on the surface which will enable applications in the future.