The effect of transformations induced by annealing at different temperatures (450<Ta<1000 °C) on the structure and magnetic properties of acicular α-Fe2O3 particles (major axis: 330±50 nm; minor axis: 70±10 nm) have been investigated by X-ray diffraction, TEM, SEM and magnetization measurements. The particles were prepared by hydrolysis and polymerization in an aqueous solution of FeCl3. In the as-prepared sample, particles are constituted by small units (3-5 nm) separated by a less dense interlayer, while keeping the same crystallographic orientation. With increasing Ta, the sample microstructure evolves towards a collapse of the small units and then to a coalescence of particles. Coherently, the spin reorientation Morin temperature TM increases with Ta, the highest value (TM = 259 K) being comparable to that of the bulk sample.

cited By 44; Conference of Proceedings of the 1999 4th International Workshop on Metastable Phases: Magnetic Structural and Transport Properties of Nanostructured Materials and Composites, New Properties and Functional Applications ; Conference Date: 7 April 1999 Through 9 April 1999; Conference Code:56114