The effects of prolonged milling in air and vacuum on BaFe12O19 ionic
crystal structure and particles morphology have been analysed. X-ray d
iffraction, scanning electron microscopy and thermal analysis experime
nts show that for vacuum-milled material the ordered structure transfo
rms progressively into a stable disordered nanocrystalline phase. For
air-milled samples, apart from structural transformation, chemical dec
omposition was found.