  A plethora of modern technologies rely on permanent magnets for their
operation, including many related to the transition towards a sustainable
future, such as wind turbines or electric vehicles. Despite the overwhelming
superiority of magnets based on rare-earth elements in terms of the magnetic
performance, the harmful environmental impact of the mining of these raw
materials, their uneven distribution on Earth and various political conflicts
among countries leave no option but seeking for rare-earth-free alternatives.
The family of the hexagonal ferrites or hexaferrites, and in particular the
barium and strontium M-type ferrites (BaFe12O19 and SrFe12O19), are strong
candidates for a partial rare-earth magnets substitution, and they are indeed
successfully implemented in multiple applications. The manufacturing of
hexaferrites into dense pieces (i.e. magnets) meeting the requirements of the
specific application (e.g. magnetic and mechanical properties, shape) is not
always straightforward, which has in many cases hampered the actual
substitution at the industrial level. Here, past and on-going research on
hexaferrites sintering is reviewed with a historical perspective, focusing on
the challenges encountered and the solutions explored, and correlating the
sintering approaches with the magnetic performance of the resulting ceramic
magnet.
