Effects of interparticle interaction in ferromagnetic nanoparticle systems.

The effect of interparticle interaction in ferromagnetic nanoparticle systems is reviewed focusing on metallic nanoparticles in an insulating host. Strong dipolar interparticle interactions may give rise to a superspin glass phase with dynamical properties radically different from the superparamagnetic relaxation displayed by non-interacting or only weakly interacting nanoparticles. Strong exchange coupling in nanoparticle systems with a volume concentration above the threshold for geometrical percolation induces ferromagnetism.