Competition between dipolar and exchange interparticle interactions in magnetic nanoparticle films

The concentration dependence of the remanence, the coercivity and the blocking temperature of a three-dimensional random assembly of ferromagnetic nanoparticles interacting via exchange and dipolar forces is studied by Monte Carlo simulations. We find that interactions always suppress the coercivity, while they have opposite effects on the remanence of the sample. The crossover from dipolar-coupled to exchange-coupled behavior occurs when the two types of interactions have comparable strengths. The blocking temperature is always enhanced due to interactions, except for the case that particles coalesce and the sample is above the percolation threshold. (C) 2003 Elsevier Science B.V. All rights reserved.