Previous studies of the magnetic properties of antiferromagnetic NiO nanoparticles have mainly been performed on strongly aggregated particles without taking the e!ects of inter-particle interactions into account. To address this problem we demonstrate that by treating such samples with low-energy ball milling it is possible to physically separate the particles without inducing changes in the particle size and shape. Both as-prepared and separated NiO nanoparticles, with and without Fe doping, have been studied by MoK ssbauer spectroscopy and magnetisation measurements. Here, we show that inter-particle interactions can have a strong e!ect on the superparamagnetic relaxation behaviour of NiO nanoparticles. 2000 Elsevier Science B.V. All rights reserved. PACS: 75.50.Ee; 75.50.Tt; 75.60.!d; 76.80.#y