Annealing effects on magnetic properties of acicular hematite nanoparticles

The effect of transformation on the structure and magnetic properties of a-Fe2O3 acicular nanoparticles (major axis, .apprx.330 nm; minor axis, .apprx.70 nm) was studied. The particles were prepd. by hydrolysis and polymn. in an aq. soln. of FeCl3. Particles in the as-prepd. sample are constituted by sub-units of 3-5 nm. The changes in the magnetic properties of the samples under thermal treatments (e.g. Morin transition, superparamagnetic behavior) are mainly caused by the coalesce of the sub-units and by the variation of the crystallinity of nanoparticles.