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. •Core–shell powders composed of ferromagnetic particles and ferrite coatings are designed.•Electroinsulating coating has a structure of ferrite bilayer.•Coating on spherical FeSi particles consists mainly of Fe3O4 and minimum NiFe2O4.•Coating on permalloy particles consists mainly of NiFe2O4 and minimum Fe3O4.