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Systematic studies of the magnetic properties of magnetic nanoparticles from FeraSpin R and the FeraSpin Series with respect to their suitability as tracers for magnetic particle imaging are presented. Magnetic particle spectroscopy measurements indicate that FeraSpin R exhibits a harmonic spectrum very similar to that of Resovist, whereas FeraSpin L, XL, and XXL show a 2.5-fold increase of harmonic amplitudes compared to FeraSpin R. To understand the differences between the various samples of the FeraSpin Series, representing size-selected, narrowly distributed particles of identical composition extracted from FeraSpin R, measurements of the ac susceptibility (ACS), magnetorelaxometry (MRX), and static M-H curves were performed on suspended and immobilized particle samples. ACS and MRX measurements on immobilized samples indicate a wide distribution of anisotropy energies despite the narrow distribution of hydrodynamic sizes. Static magnetization measurements show that all samples exhibit a bimodal distribution of magnetic moments: The fraction of larger moments corresponds to the contribution from the overall particle core, whereas the smaller is attributed to the contribution from the crystallites comprising the core.