Ultrafast Heating Rate of Ultrasmall Gold-coated Iron Oxide Magnetic Nanoparticles by Ferromagnetic Resonance

In this study, we experimentally demonstrated an ultrafast heating rate of ultrasmall gold-coated iron oxide magnetic nanoparticles (Fe
3
O
4
@Au NPs) by the ferromagnetic resonance (FMR) effect. Using the constructed setup, the ferromagnetic resonance and temperature increment of NPs under FMR were evaluated. The resonant frequency of Fe
3
O
4
@Au NPs and their uncoated Fe
3
O
4
NPs was several GHz and increased with increasing DC field strength. The resonant frequency of Fe
3
O
4
@Au NPs shifted slightly lower than that of Fe
3
O
4
NPs. The initial temperature rising rate reached the maximum values at their corresponding DC fields for FMR (e.g. 1.294 and 3.894 K/s under H
DC
=1200 Oe for RF field of f
AC
=4 GHz and H
AC
=4 Oe for Fe
3
O
4
@Au and Fe
3
O
4
NPs, respectively). These values were two orders of magnitude higher than that of Néel and the Brownian relaxation for the conventional magnetic hyperthermia. The maximum value also increased with increasing RF field frequency. The obtained results also indicate that it is possible to control the temperature of NPs by adjusting the parameters of the RF field and DC field, suggesting their potential use for therapeutic temperature control in magnetic hyperthermia applications.