  Magnetic high entropy alloys (HEAs) are a new category of high-performance
magnetic materials, with multi-component concentrated compositions and complex
multi-phase structures. Although there have been numerous reports of their
interesting magnetic properties, there is very limited understanding about the
interplay between their hierarchical multi-phase structures and their local
magnetic structures. By employing high spatial resolution correlative magnetic,
structural and chemical studies, we reveal the influence of a hierarchically
decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of
magnetic vortex states within individual A2 (disordered BCC) precipitates,
which are distributed in an ordered B2 matrix that is weakly ferromagnetic.
Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains
of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are
also observed. These results provide important insight into the origin of
coercivity in this HEA, which can be attributed to a complex magnetization
process that includes the successive reversal of magnetic vortices.
