Role of magnetic interparticle coupling on the field dependence of the superparamagnetic relaxation time

Magnetic properties of Co-SiO2 granular films are displayed and explained by means of a phenomenological model that takes into account the effects of magnetic interparticle coupling on the superparamagnetic relaxation behavior. The model is based on the analysis of coupled nanoparticles through a modified random anisotropy model that takes into account the concentration and size of the nanoscopic particles, as well as the field dependence of the correlation length. The proposed model leads to an accurate description of the field dependence of the blocking temperature, substantially better than the power law usually employed to describe noninteracting particles.