  The diversity of three-dimensional magnetic states in a FeGe nanocylinder is
studied using micromagnetic simulations and off-axis electron holography in the
transmission electron microscope. In particular, we report the observation of a
dipole string -- a spin texture composed of two coupled Bloch points -- which
becomes stable under geometrical confinement. Quantitative agreement is
obtained between experimental and theoretical phase shift images by taking into
account the presence of a damaged layer on the surface of the nanocylinder. The
theoretical model is based on the assumption that the damaged surface layer,
which results from focused ion beam milling during sample preparation, has
similar magnetic properties to those of an amorphous FeGe alloy. The results
highlight the importance of considering the magnetic properties of the surface
layers of such nanoscale samples, which influence their magnetic states.
