Reciprocal space tomography of 3D skyrmion lattice order in a chiral magnet

Significance Magnetic skyrmion lattices have exceptional properties, making them ideally suited for a new generation of spintronics devices. As devices are surface-dominated, a key question concerns the influence of surfaces on the spin structure. While a wide range of methods exist for studies of 2D skyrmions, the detailed knowledge of 3D magnetic structures has remained elusive. Here we use tomographic resonant elastic X-ray scattering to reconstruct the depth dependence of a 3D skyrmion crystal order in Cu 2 OSeO 3 . We find a continuous transformation with increasing depth from complete Néel-type winding at the surface to the Bloch-type winding in the bulk. Our study suggests the importance of free surfaces has been severely underestimated and will be of central importance for future skyrmionics applications.