Iron oxide nanoparticles are often used in medical technology as contrast agents for magnetic resonance imaging or as transport agents for drugs in the bloodstream, for example in tumor therapy. For these applications, the nanoparticles have to be biocompatible and superparamagnetic. Thus, they must be strongly magnetizable in a magnetic field and also must lose their magnetization when the magnetic field is switched off. Using analytical high-resolution transmission electron microscopy, a team at TU Bergakademie Freiberg investigated how the magnetic properties of the nanoparticles can further be improved via microstructure design.