Structure and magnetic properties of thermally treated nanohematite

The effect of modification induced by thermal treatment on the structure and magnetic properties of alpha -Fe2O3 romboedrical nanoparticles (similar to 30 nm) synthesized by chemical route has been analyzed by X-ray diffraction, transmission electron microscopy, magnetization measurements and Mossbauer spectroscopy. Annealing of these samples recrystallizes the nanoparticles maintaining their mean size while changing the crystalline anisotropy nanoparticles energy, thus leading to an increase of the spin reorientation Morin temperature and changes in the superparamagnetic-blocking behavior. (C) 2001 Elsevier Science B.V. All rights reserved.