Magnetic Behaviour of Core/Shell Nanoparticle Assemblies: Interparticle Interactions Effects

Interparticle interactions in assemblies of nanoparticles represent an important effect that modifies their magnetic behavior. The characteristics of the hysteresis loop and the temperature dependent magnetization (field cooled (FC)/zero-field cooled (ZFC)) are studied numerically in magnetic nanoparticle assemblies using Monte Carlo simulations and the standard Metropolis algorithm. We study composite spin nanostructures with ferromagnetic (FM) core/antiferromagnetic (AFM) shell morphology and simple ferromagnetic nanostructures. Both three-dimensional granular solids and two-dimensional ordered nanoparticle arrays are analyzed and compared, with emphasis on the interplay between single-particle characteristics and magnetostatic interparticle interactions. We find that the antiferromagnetic interface provides a strong exchange coupling with the ferromagnetic core and, through it, an effective long range interparticle correlation, modified from that of simple FM nanostructures. The results of our simulations are compared with experimental findings.