Self-diffusion in ferrogranulates: Stockmayer model revisited

We present a systematic numerical study of a quasi-two-dimensional mixed system composed of Stockmayer-type dipolar particles and purely repulsive non-polar particles. By combining detailed cluster analysis with a quantitative evaluation of self-diffusion, we demonstrate how the interplay between particle area fraction, dipolar interactions, and an out-of-plane magnetic induction governs the structural organisation and dynamical behaviour of the mixture. We show that, in the absence of induction, isolated magnetic particles diffuse essentially in a Gaussian manner across all concentrations. At longer time scales, by contrast, the system enters a crowding-dominated diffusive regime, in which both the diffusion exponent and the non-Gaussianity vary monotonically with area fraction. Our findings provide a framework for interpreting diffusion phenomena in ferrogranular materials and pave the way for future experimental verification, particularly regarding induction-controlled cooling of non-magnetic components. • A quasi-2D mixture of Stockmayer dipolar particles and purely repulsive non-polar particles is systematically analysed using large-scale Langevin dynamics simulations. • The combined effects of particle area fraction, dipolar interactions, and out-of-plane magnetic induction on cluster formation and dynamical behaviour are quantified. • Isolated magnetic particles diffuse in an essentially Gaussian manner without induction, while crowding induces subdiffusivity and enhanced non-Gaussianity at longer time scales. • Strong magnetic induction restructures dipolar aggregates and indirectly slows down the diffusion of non-magnetic particles, producing a “magnetic freezing” effect. • The results provide a mechanistic framework for interpreting structure-diffusion coupling in ferrogranular materials and suggest directions for future experimental verification.