Magnetic property of NiO ultrafine particles with a small Ni core

The magnetic nature of a NiO shell and a Ni core were separately investigated in the temperature dependence of the magnetization curve of the samples with the average sizes of 1.6, 2.0, 2.2, 2.5, 2.8, 3.0 and 3.2 nm. The superparamagnetism of the NiO shell and Ni core were observed in specific temperature ranges. The increase of the magnetic moment per atom in the metallic free cluster with decreasing size were not observed in the small Ni core with the NiO shell though the proper saturation magnetization of Ni core was estimated. (C) 1997 American Vacuum Society. [S0734-211X(97)05104-4].