Annealing effects on magnetic properties of acicular hematite nanoparticles

The effect of transformation on the structure and magnetic properties of alpha-Fe(2)O(3) acicular nanoparticles (major axis, similar to 330 nm; minor axis, similar to 70 nm) has been investigated. The particles were prepared by hydrolysis and polymerization in an aqueous solution of FeCl(3). Particles in the as-prepared sample are constituted by sub-units of 3-5 nm. The results indicate that the changes in the magnetic properties of the samples under thermal treatments (e.g. Morin transition, superparamagnetic behaviour) are mainly caused by the coalesce of the sub-units and by the variation of the crystallinity of nanoparticles. (C) 2002 Elsevier Science B.V. All rights reserved.