STATIC AND DYNAMICAL PROPERTIES OF GAMMA-FE2O3 NANOPARTICLES

Several series of gamma-Fe2O3 nanoparticles dispersed in a polymer hav e been studied by means of various techniques. The variation of the re laxation time of the magnetic moment of the particle is in very good a greement with the Neel-Brown and our interparticle interaction models which lead to a reduced damping constant varying between 0.08 and 1. F or non interacting particles, the main component of the anisotropy com es from the surface. For interacting particles, the interaction energy includes dipolar and surface induced contributions. The susceptibilit y in the superparamagnetic state shows a strong dependence of the resu lts on the external shape of the sample and the direction of applied f ield, very well checked experimentally, which is well interpreted with the Onsager model.