Evaluation of Different Magnetic Particle Systems with Respect to Its MPI Performance

The Magnetic Particle Spectroscopy (MPS)-amplitudes were measured on 7 suspensions of magnetite based magnetic particles (MNP) differing in core size and magnetic anisotropy. The distributions of the effective domain sizes, estimated by means of quasistatic M(H) measurements and Magnetorelaxometry (MRX), matches well the core size distribution for the single core MNP-systems estimated by electron microscopy. Two systems, namely Resovist and M4E clearly exhibit a bimodal domain size distribution. It was shown, that the MPS amplitudes strongly increase with increasing domain size up to 21 nm, the mean value of the larger fraction of Resovist. For M4E with a mean size of the larger fraction of 33 nm the measured MPS-amplitudes became much smaller than those of Resovist, in particular for the higher harmonics. That behaviour was attributed to the mean anisotropy energy of these MNPs, estimated by MRX, exceeding that of Resovist by one order of magnitude. The effect of the MNP’s magnetic anisotropy is also supported by comparison of measured MPS-amplitudes with those which were calculated on the base of M(H)-data.