  The magnetic configurations of cylindrical Co-rich CoNi nanowires have been
quantitatively analyzed at the nanoscale by electron holography and correlated
to local structural and chemical properties. The nanowires display grains of
both face-centered cubic (fcc) and hexagonal close packed (hcp) crystal
structures, with grain boundaries parallel to the nanowire axis direction.
Electron holography evidences the existence of a complex exotic magnetic
configuration characterized by two distinctly different types of magnetic
configurations within a single nanowire: an array of periodical vortices
separating small transverse domains in hcp rich regions with perpendicular easy
axis orientation, and a mostly axial configuration parallel to the nanowire
axis in regions with fcc grains. These vastly different domains are found to be
caused by local variations in the chemical composition modifying the
crystalline orientation and/or structure, which give rise to change in magnetic
aniso-tropies. Micromagnetic simulations, including the structural properties
that have been experimentally determined, allows for a deeper understanding of
the complex magnetic states observed by electron holography.
