Dynamics of magnetic nanoparticle suspensions

Abstract

We study the dynamical response of suspensions of single-domain magnetic nanoparticles. The effect of sample parameters on Neel and Brownian relaxation times which characterize the response is studied. Their effect on the ac susceptibility is also investigated. As the relaxation times are strongly size dependent we study the effect of polydispersity on the response functions next. A procedure to extract particle-size distribution in polydisperse samples from Cole–Cole plots is provided. Further, the presence of attractive and repulsive interactions amongst MNP yields a distribution of clusters of varying sizes. We propose a model incorporating the phenomena of aggregation and fragmentation to understand the formation of clusters and their distributions. Finally, we compare our numerical results with the experimental data. These comparisons are satisfactory.