SPIONs self-assembly and magnetic sedimentation in quadrupole magnets: Gaining insight into the separation mechanisms

•Magnetic sedimentation of 5–30 nm SPIONs under horizontal fields and gradients.•Dipole-dipole interactions and magnetic/gravitational forces induce separation.•Particle self-assembly is also responsible for the sedimentation.•The separation and sedimentation processes occur in less than 1 h.