Chemically bonded clusters (CB-cluster) were prepared from PEI and PAM-coated MNPs. The electrostatically clustered units (ES-cluster) are smaller and more compact. The electrostatic adhesion and the amide bond formation were confirmed by ATR-FTIR. CB-cluster dispersions are colloidally stable under physiological conditions. CB-cluster shows great potential for application in MRI and hyperthermia.