Magnetic iron oxide nanoparticles have multiple biomedical applications in AC-field hyperthermia and magnetic resonance imaging (MRI) contrast enhancement. Here, two cubic particle suspensions are analyzed in detail, one suspension displayed strong magnetic heating and MRI contrast efficacies, while the other responded weakly. This is despite them having almost identical size, morphology, and colloidal dispersion. Aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy analysis confirmed that the spinel phase Fe3O4 was present in both samples and identified prominent crystal lattice defects for the weakly responding one. These are interpreted as frustrating the orientation of the moment within the cubic crystals. The relationship between crystal integrity and the moment magnitude and dynamics is elucidated for the case of fully dispersed single nanocubes, and its connection with the emergent hyperthermia and MRI contrast responses is established.
© 2022 The Authors. Published by American Chemical Society.