Magnetic behavior of dense nanoparticle assemblies: Interplay of interparticle interactions and particle system morphology

The role of interparticle interactions and the morphology in the magnetic behavior of dense assemblies of Fe nanoparticles with concentration well above the percolation threshold has been studied using the Monte Carlo simulations technique. The initial and temperature-dependent magnetization curves have been calculated for different conditions of the assembly morphology and the interparticle interaction strengths. Our simulations showed that the strong competition between the anisotropy and exchange energies in nonuniform dense assemblies results in a frustration of the nanoparticles moments coupling and creates plateaus and abrupt steps, which indicate a sudden, collective spin reversal, for low and intermediate dipolar strengths. In the case of strong dipolar interactions, the stepwise behavior becomes smoother and gradually disappears.