The interplay between single particle anisotropy and interparticle interactions in ensembles of magnetic nanoparticles

This paper aims to analyze the competition of single particle anisotropy and interparticle interactions in
nanoparticle ensembles using a random anisotropy model. The model is first applied to ideal systems of
non-interacting and strongly dipolar interacting ensembles of maghemite nanoparticles. The investigation is
then extended to more complex systems of pure cobalt ferrite CoFe2O4 (CFO) and mixed cobalt-nickel
ferrite (Co,Ni)Fe2O4 (CNFO) nanoparticles. Both samples were synthetized by the polyol process and
exhibit the same particle size (DTEM E 5 nm), but with different interparticle interaction strengths and
single particle anisotropy. The implementation of the random anisotropy model allows investigation of
the influence of single particle anisotropy and interparticle interactions, and sheds light on their complex
interplay as well as on their individual contribution. This analysis is of fundamental importance in order
to understand the physics of these systems and to develop technological applications based on concentrated
magnetic nanoparticles, where single and collective behaviors coexist.