Magnetic Dipolar Interactions in Nanoparticle Systems: Theory, Simulations and Ferromagnetic Resonance

Summary

Magnetic nanoparticle assemblies present novel magnetic properties with respect to their bulk constituent components. In addition to the surface effects produced by the modified atomic symmetry in such low dimensional systems, the magnetic coupling between the particles also plays a significant role in determining the overall magnetic behavior of a magnetic nanoparticle assembly. In this Chapter, we describe a theoretical model that accounts for the dipolar magnetic interaction between particles. There are two fundamental aspects of interest in our studies: the spatial distribution of the particles and density of the particle. These aspects have been addressed in our simulations, where we have performed simulations for regular and random arrays of particles. We will discuss the general theory of ferromagnetic resonance (FMR) applied to such systems and how the specific dipolar interactions can be incorporated for nanoparticle systems. The spatial distribution of particles can give valuable information of the strength of the dipolar interaction between them and we will demonstrate how this can be used in real systems. We have performed FMR experiments on nanoparticle assemblies of γ – Fe₂O₃ nanoparticles with different average particle sizes (2.7–7.3 nm) and particle densities, where samples are in rectangular slab shape. Measurements were performed as a function of the angle between the sample plane and applied magnetic field. Recent studies have shown that the incorporation of the dipolar interactions into FMR theory can explain the experimental results for angular studies in magnetic nanoparticle assemblies [1].