Fabrication of rare-earth free permanent magnets using Co nanorods : in situ studies of the directed assembly and compaction under external

The fabrication of performant rare-earth free permanent magnets (PM) using single crystalline Co nanorods (NRs) requires to control the formation of dense and parallel assemblies from a colloidal suspension. These assemblies results from a complex 3-steps dynamic process occurring with very different time-scales : i) the NR alignment under an external field (ms), ii) their migration toward zones of high field gradient (s) and iii) their densification during the drying step (min). In operando studies coupling USAXS, SAXS and WAXS will allow to follow in real time the migration and the densification of Co NRs under magnetic field at the characteristic length of the NR crystallites (Å), interparticle distance (10’s - 100’s of nm) and of the pre-aligned fibers (µm). The impact of the experimental parameters (solvent, concentration, magnetic field) on the orientation distribution function will allow guiding the fabrication of rare-earth free PM with enhanced properties.