Understanding dynamics of interacting magnetic nanoparticles: From the weak interaction regime to the collective superspin glass state

A brief review of the investigations on interparticle interaction effects (weak and strong interactions regimes) is reported with a special emphasis on the critical behaviour in the static and dynamical properties and on the out of equilibrium dynamics of the collective superspin glass (SSG) state. The results of the investigation of aging and memory effects in two peculiar SSG systems are discussed: MnFe2O4 nanoparticles, in powder form, with very strong dipolar interactions, and a diluted system, consisting of a film of Co particles dispersed (5% volume fraction) in a Mn matrix, where interparticle interactions are mainly mediated by the matrix. © Published under licence by IOP Publishing Ltd.