MAGNETIC CLUSTERS DEVELOPMENT IN OXIDIZED CeNi5 POWDER

Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and magnetic measurements at low temperature of Ni metallic clusters covered by NiO, Ce2O3 and CeO2, obtained from CeNi5 powder oxidized in air at different temperatures up to 800°C, are reported. The average crystallite size of Ni core and the thickness of NiO oxide formed at the surface increase with temperature due to recrystallization processes, from 34 nm at 300°C to 77 nm at 800°C and from 9 nm to 19 nm, respectively. Ni metallic component was detected both in XPS valence bands and core levels spectra only after sputtering. The hysteresis loop presents a small shift towards negative magnetic fields which confirms the presence of ferromagnetic Ni/antiferromagnetic NiO interfaces.