Chemical synthesis of nickel ferrite spinel designed as an insulating bilayer coating on ferromagnetic particles

Soft magnetic core-shell particles were designed by coating FeSi and permalloy powders with ferrite nanoparticles. The permalloy-type powder particles were prepared by mechanical alloying process of 80 wt% of Ni, 14.7 wt% of Fe, 4.4 wt% of Mo, 0.5 wt% of Mn and 0.3 wt% Si. NiFe2O4 cuboidal nanoparticles were synthesized by the chemical precipitation of hydroxides by alkaline treatment of the dissolved metal in aqueous chloride solution and the same process was used for a deposition of NiFe2O4 nanoparticles on both substrates. The average size of NiFe2O4 nanoparticles, crystallinity and spinel structure were determined by TEM and XRD techniques. The deposited coating was created in a bilayer form. The composition of individual layer was analyzed by XRD and TEM using 100-nm lamella extracted from the coating by focused ion beam. The chemical composition of individual layers was analyzed by EDX analysis. The specific electric resistivity measurement has confirmed a good insulating character of the designed bilayer coating, whereas the prepared core-shell powders and relevant green compacts belong to soft magnetic materials.