The “field or frequency” dilemma in magnetic hyperthermia: The case of Zn Mn ferrite nanoparticles

Abstract

• The conversion efficiency of electromagnetic energy to thermal energy is improved. • The SAR and ILP of Zn Mn ferrite MNPs is maximized with respect to the Zn content. • The optimum frequency of AC magnetic field decreases with the average MNPs size. • The SAR of the large MNPs has the super-quadratic dependence on the magnetic field. • The activation of Brown heating mechanism is shown for MNPs suspension in glycerol . The efficiency of conversion of electromagnetic energy into heat is a key factor for magnetic nanoparticles (MNPs) utilization in magnetic hyperthermia as well as in advanced magnetothermal medical techniques. Currently, the need to improve the MNPs heat release results in the increase of weight, size and power of alternating current (AC) facility and the aggravating side effects on health tissues. The aim of our work is to address these problems by offering a new strategy for improving the heat release at a relatively low frequency using ferrite based MNPs. We demonstrate nontrivial dependence of MNPs heat release on the amplitude of the AC magnetic field in zinc manganese ferrite Zn 0.2 Mn 0.8 Fe 2 O 4 MNPs (close to 5th power instead of a well-known quadratic). Our studies challenge the current conventional approaches based on the minimization of magnetic field amplitude. We offer a better strategy: to increase the amplitude while reducing the frequency to exploit the full potential of superquadratic law for amplitude dependence of heat output. We believe that this research should have a profound impact on a number of advanced biomedical applications of MNPs and magnetic hyperthermia.