X-ray absorption studies of nanocrystalline Ni

The x-ray absorption was investigated for nanocrystalline Ni, bulk Ni, and NiO. The size of nanocrystalline Ni is roughly 22 nm. From the k edge spectrum studies, we find that the bond lengths in both nanocrystalline and bulk Ni are completely the same, however, the ordering factor is manifestly reduced for nanocrystalline Ni. The calculated coordination number of nanocrystalline Ni is 11.7 which is smaller than the number of nearest neighbor 12 in bulk Ni. The ordering factor and the coordination number of nanocrystalline Ni increase to the same value of bulk Ni after annealing in vacuum at 1600 K for 24 hrs. From this study, we can clearly identify the surface oxidation effect in nanocrystalline Ni. This strongly supports the magnetic anisotropy effect which occurs only in nanocrystalline Ni. The magnetization enhancement near 40 K for the nanocrystalline Ni is related to the exchange anisotropy effect. (C) 1997 Acta Acta Metallurgica Inc.