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

In this study, we demonstrated experimental findings on the ultrafast heating capabilities of ultrasmall gold-coated iron oxide magnetic nanoparticles (MNPs) (Fe3O4 @ Au NPs) utilizing the ferromagnetic resonance (FMR) effect. A lab-made setup was employed to evaluate the FMR and temperature increment of NPs under FMR conditions. The resonant frequency of both Fe3O4 @ Au NPs and their uncoated Fe3O4 NPs was several GHz and increased with the strength of the applied dc field as accurately described by the Kittel equation. At a given dc field, the resonant frequency of Fe3O4 @ Au NPs slightly shifted lower than compared to Fe3O4 NPs. Remarkably, the initial temperature rising rate reached maximum values corresponding to the dc fields for FMR condition (e.g., 1.294 °/s and 3.894 °C/s under
$H_{\text {DC}}= 1200$
Oe for RF field of
$f_{\text {AC}}= 4$
GHz and
$H_{\text {AC}}= 4$
Oe for Fe3O4 @ Au and Fe3O4 NPs, respectively). These values were two orders of magnitude higher than that of Néel-Brownian relaxation for conventional magnetic hyperthermia (MH). Furthermore, the maximum value of the heating rate increased with higher RF field frequencies. These results demonstrate the potential of controlling the temperature of NPs by adjusting RF field and dc field parameters, offering promising prospects for therapeutic temperature control in MH applications.