These surfactants prevent the nanoparticles from clumping together, so the particles can not fall out of suspension nor clump into a pile of magnetic dust on near the magnet. The magnetic particles in an ideal ferrofluid never settle out, even when exposed to a strong magnetic field. A surfactant has a polar head and non-polar tail (or vice versa), one of which adsorbs to a nanoparticle, while the non-polar tail (or polar head) sticks out into the carrier medium, forming an inverse or regular micelle, respectively, around the particle. electrostatic repulsion then prevents agglomeration of the particles.