Dipolar interaction and size effects in powder samples of colloidal iron oxide nanoparticles

Dipole-dipole interactions in nanostructured materials deeply affect their magnetic properties, and detailed studies are still required to fully understand them. In this work, the dependence of magnetic properties on particle size has been evaluated in powder samples of Fe oxide nanoparticles produced by colloidal methods. Zero-field-cooled and field-cooled magnetization curves and magnetization versus applied field data have been analysed by taking into account dipolar interactions through a correction to the classical superparamagnetic model. Morphological and magnetic data were in very good agreement, which has allowed us to quantify relevant physical parameters, such as the anisotropy constant, magnetic moment, and interacting volume for our system.