Effective uniaxial anisotropy in optimized magnetite MPI tracers probed by freezing in a magnetic field

Magnetic particle imaging (MPI) relies on the specific non-linear magnetization response of superparamagnetic nanoparticle tracers for signal generation. Tracers should be tuned for optimal size distributions and magnetization responses under alternating magnetic field. Therefore, comprehensive understanding of the nanoparticle magnetization dynamics is necessary for producing efficient MPI tracers. In this study, we evaluated the dynamics of magnetization reversal of an optimized MPI tracer [1] after restricting the particle´s motion by freezing the solvent. Furthermore, we used an aligning field during freezing to introduce a preferred magnetization direction. The results indicate that the tracer magnetization response can be approximated by an effective uniaxial anisotropy despite the particle´s cubic point group symmetry.