Dipolar interactions among magnetic dipoles of iron oxide particles dispersed in mili-size hydrogel beads

•PVA/iron oxide milli-size beads were synthesized by means of a one-pot route.•Effective demagnetizing factor (NE) is tested in beads and superstructures of beads.•The increase of the ac susceptibility as a function of hydration agrees with the diminution of dipolar interactions.•Isothermal magnetization experiments are described by considering two hierarchies of clustering.•The NE proves to be an efficient tool for the analysis of complex 3d dispersions of magnetic nanoparticles.