Field-swept magnetic particle spectroscopy using a transverse DC field

The transverse magnetization of magnetic nanoparticles (MNPs) induced by a DC field perpendicular to the AC field is of increasing interest in magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS). It can be used to improve the image quality in MPI and to enhance the sensitivity of MPS without direct feedthrough interference. In this work, we developed a field-swept MPS to observe the response curve of the transverse magnetization by varying the transverse DC field amplitude, and reported a new metric to characterize the nonlinear properties of MNPs, called DCM (the DC field amplitude at the maximum harmonic amplitude). Two commercial MNPs (synomag®-70 and synomag®-50) were investigated. The experimental results show that the DCM is different for the two MNPs and independent of the concentration of MNPs. In addition, the DCM was positively correlated with the viscosity of the sample solvent, which further indicates a correlation with Brownian relaxation