Superparamagnetic colloid suspensions: Water magnetic relaxation and clustering

Ferrite superparamagnetic (SPM) nanoparticles in aqueous suspensions shorten the nuclear magnetic relaxation of water protons. For transverse relaxation, that effect is enhanced when agglomeration of elementary SPM cores occurs, because of an increase of the secular part of the transverse relaxivity. On the contrary, clustering weakens the T1-shortening, in agreement with the prediction of a new model for diffusion.