Optimization of excitation field depending on magnetic nanoparticle parameters for magnetic hyperthermia under safety constraint

Hysteresis loss (P) of magnetic nanoparticles (MNPs) under alternating current excitation has been used to induce hyperthermia in cancer cells. We theoretically optimized the excitation field amplitude Hac and frequency f required to maximize P, while the product C = Hacf did not exceed a threshold value to avoid side effects in biomedical applications. We obtained analytical expressions for the optimum values of Hac and f as functions of C and MNP parameters. Almost the same P could be obtained for MNPs with magnetic core diameters dc ranging over 20–40 nm if Hac and f were optimized according to the dc value. A numerical example was a P of ∼0.4 kW/g Fe for immobilized MNPs under C = 2 × 109 A/(ms). We also examined the dependences of P on MNP parameters under the optimum excitation field. A large saturation magnetization was essential for a large P. The degradation of P caused by the dc distribution in a practical (realistic) sample was examined, and the conditions that reduce degradation were determined. There was a strong agreement among these properties between the analyses and numerical simulations. Finally, we showed how much P increased for suspended MNPs relative to that for immobilized MNPs. Overall, these results will be useful for the development of high-performance hyperthermia systems.