The incorporation of Zn2+ dopants in tetrahedral sites leads to the successful magnetism tuning of spinel metal ferrite nanoparticles (see picture). (Zn0.4Mn0.6)Fe2O4nanoparticles exhibit the highest magnetization value among the metal ferrite nanoparticles. Such high magnetism results in the largest MRI contrast effects (r2=860 mm−1 s−1) reported to date and also huge hyperthermic effects.