  The scientific and technological exploration of artificially designed
three-dimensional magnetic nanostructures opens the path to exciting novel
physical phenomena, originating from the increased complexity in spin textures,
topology, and frustration in three dimensions. Theory predicts that the
equilibrium magnetic ground state of two-dimensional systems which reflects the
competition between symmetric (Heisenberg) and antisymmetric
(Dzyaloshinskii-Moriya interaction (DMI)) exchange interaction is significantly
modified on curved surfaces when the radius of local curvature becomes
comparable to fundamental magnetic length scales. Here, we present an
experimental study of the spin texture in an 8 nm thin magnetic multilayer with
growth-induced in-plane anisotropy and DMI deposited onto the curved surface of
a 1.8 {\mu}m long non-magnetic carbon nanowire with a 67 nm radius. Using
magnetic soft x-ray tomography the three-dimensional spin configuration in this
nanotube was retrieved with about 30nm spatial resolution. The transition
between two vortex configurations on the two ends of the nanotube with opposite
circulation occurs through a domain wall that is aligned at an inclined angle
relative to the wire axis. Three-dimensional micromagnetic simulations support
the experimental observations and represent a visualization of the
curvature-mediated DMI. They also allow a quantitative estimate of the DMI
value for the magnetic multilayered nanotube.
