We have characterized fractionated magnetic nanoparticles (MNPs) for magnetic particle imaging. Original Ferucarbotran particles were magnetically divided into three fractionated MNPs called MS1, MS2, and MS3. Harmonic spectra from the three fractionated MNPs were measured at excitation fields of 2.8 and 28 mT with a frequency of 10 kHz. MS1 showed a 2.5-fold increase in the harmonic spectrum over that of the original MNPs. To understand the origin of the enhancement in the harmonic spectrum from MS1, we explored the magnetic properties of the MS series, such as distributions of effective core size and anisotropy energy barrier, and the correlation between them. Using these results, we performed numerical simulations of the harmonic spectra based on the Langevin equation. The simulation results quantitatively explained the experimental results of the fractionated MS series. It was also clarified that MS1 includes a large portion of the MNPs that are responsible for the harmonic spectrum.
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