Temperature dependence of the magnetic interactions taking place in monodisperse magnetite nanoparticles having different morphologies

We report on the temperature dependence of the interactions present in single crystal magnetite nanoparticles having octahedral and spherical morphologies. From our results we conclude that the inter-particle interactions are, at all temperatures and in both octahedral and spherical nanoparticles, demagnetizing in nature. These interactions are not describable in terms of a mean field but local and linked to the poles present at the surfaces of the particles and particles clusters. In both samples, the peak on the field dependence of the interactions has an associated maximum that decreases in magnitude with an increase of the measuring temperature. Also, that peak gets narrower when the temperature is increased. The high order multipolar moments of the octahedral nanoparticles, originated by the fact that their morphology includes the presence of edges an dihedra, is detectable in the larger field range in which the interactions are observable in these samples in comparison with that corresponding to the spherical nanoparticles, exhibiting close-to-dipolar moments.