  Complex 3D magnetic textures in nanomagnets exhibit rich physical properties,
for example in their dynamic interaction with external fields and currents, and
play an increasing role for current technological challenges such as
energy-efficient memory devices. To study these magnetic nanostructures
including their dependency on geometry, composition and crystallinity, a 3D
characterization of the magnetic field with nanometer spatial resolution is
indispensable. Here we show how holographic vector field electron tomography
can reconstruct all three components of magnetic induction as well as the
electrostatic potential of a Co/Cu nanowire with sub 10\,nm spatial resolution.
We address the workflow from acquisition, via image alignment to holographic
and tomographic reconstruction. Combining the obtained tomographic data with
micromagnetic considerations we derive local key magnetic characteristics, such
as magnetization current or exchange stiffness, and demonstrate how
magnetization configurations, such as vortex states in the Co-disks, depend on
small structural variations of the as-grown nanowire.
