  Cylindrical magnetic nanowires with large transversal magnetocrystalline
anisotropy have been shown to sustain non-trivial magnetic configurations
resulting from the interplay of spatial confinement, exchange, and
anisotropies. Exploiting these peculiar 3D spin configurations and their
solitonic inhomogeneities are prospected to improve magnetization switching in
future spintronics, such as power-saving magnetic memory and logic
applications. Here we employ holographic vector field electron tomography to
reconstruct the remanent magnetic states in CoNi nanowires with 10 nm
resolution in 3D, with a particular focus on domain walls between remanent
states and ubiquitous real-structure effects stemming from irregular morphology
and anisotropy variations. By tuning the applied magnetic field direction, both
longitudinal and transverse multi-vortex states of different chiralities and
peculiar 3D features such as shifted vortex cores are stabilized. The chiral
domain wall between the longitudinal vortices of opposite chiralities exhibits
a complex 3D shape characterized by a push out of the central vortex line and a
gain in exchange and anisotropy energy. A similar complex 3D texture, including
bent vortex lines, forms at the domain boundary between transverse-vortex
states and longitudinal configurations. Micromagnetic simulations allow an
understanding of the origin of the observed complex magnetic states.
