Grain size and blocking distributions in fine particle iron oxide nanoparticles

In this paper, we describe the determination of the particle size distribution of three systems of very small particles. The particles are magnetite (Fe3O4) suspended in a carrier liquid and studies on samples with different sizes (75, 66, and 58 Angstrom) are presented. We compare the physical particle size distribution obtained by TEM with the magnetic particle size. The magnetic particle size characterisation has been determined from the magnetisation curves at room temperature and temperature decay of remanence measurements when the fluids were frozen into the solid state, which give the distribution of energy barriers. We find the existence of a bimodal distribution of particle sizes, confirmed by both the magnetic and non-magnetic studies, which becomes more evident as the particle size becomes smaller, (C) 1999 Elsevier Science B.V. All rights reserved.