Magnetic Particle Spectrometry of Fe₃O₄ Multi-Granule Nanoclusters

Magnetic particle imaging (MPI) is a novel high-resolution medical imaging method that does not use ionizing radiation, but safe iron oxide nanoparticles as contrast agents. By employing magnetite (Fe₃O₄) multi-granule nanoclusters (MGNCs), one has two control parameters: the diameter of the particles and that of granules in single particles. Here we investigate the effect of the size of the particles at constant granule size, as well as the effect of granule size at constant particle size on the magnetization reversal. The saturation magnetization M_s value increases with increasing granule diameter and particle diameter, while the coercivity H_c value reaches a maximum at a particle size of about 60 nm. MGNCs with an average particle size of 77 nm and granule diameter of 17 nm show a larger response in the higher harmonics compared to the commercial reference, FeraSpin R dispersion, at both 20 and 30 mT. This result demonstrates that the MGNC concept allows tailoring of the magnetic properties of the particles to the imaging conditions in MPI.