TAILORING OF MAGHEMITE PARTICLE SIZE IN y-FE_2O_3 -SIO_2 MAGNETIC NANOCOMPOSITES

摘要

New processes for making nanosized γ-Fe_2O_3 (maghemite) particles are of particular interest for various technological applications, mainly because of the peculiar magnetic properties. Maghemite nanoparticles are ferrimagnetic and characterized by superparamagnetic relaxation phenomenon, which is strongly affected by particle size, shape and by various surface effects. The interesting magnetic properties of nanostructured maghemite are due to finite size effects and/or high surface/volume ratio, thus making the study of the interrelation between microstructure and magnetism very appealing. To create an obstacle towards particles aggregation, the preparation of maghemite dispersed over inert matrices has been attempted. The achievement of the particle size control in these nanocomposites is certainly more difficult. Therefore most of the work is devoted to a careful investigation of the relationship among particle size and magnetic properties rather than to be addressed to find the appropriate preparation conditions which favour the particle size control.