Energy dissipation of superparamagnetic suspensions in correlation with their nonlinear response of dynamic magnetization

摘要

Nonlinear dependence of magnetization incorporated within superparamagnetic system upon magnetic field strength is basically found as the consequence of its saturation with respect to either the alignment of magnetic moments or the coexisting interparticles interactions. A mathematical approach of this nonlinearity is well described by Langevin function which takes the in-between dominance of Zeeman energy and thermal energy into account. Owing to this phenomenon, it has been huge interest to explore the capability of such superparamagnetic suspensions in biomedical fields along with the utilization of sinusoidal magnetic field to induce magnetization responses of the suspended particles. In this manner, a few amount of external field energy is dissipated during relaxation processes of the particles in which its value corresponds to the imaginary part of magnetic susceptibility. This mechanism of energy dissipation is mainly used as fundamental concept in developing magnetic hyperthermia, a temporary local heating of cancer at 43℃. Meanwhile, translation of Langevin function into polynomial form leads to a term of harmonic magnetization of which the contribution cannot be omitted in order to obtain high resolution of magnetic particle imaging while applying high field strength of alternating magnetic field.