Graphitic Carbon-Coated FeCo Nanoparticles for Enhanced Magnetic Hyperthermia Therapy

Superparamagnetic iron oxide nanoparticles are widely used for magnetic hyperthermia, yet their modest saturation magnetization limits heating efficiency. Here, a simple route to graphitic carbon–coated iron–cobalt (FeCo) nanocrystals that retain near-bulk saturation magnetization and deliver competitive heating is reported. Single-phase FeCo ingots are arc-melted, crushed, mechanically milled with graphite for 5 h under argon and annealed at 400–800 °C in forming gas to form protective graphitic shells. X-ray diffraction and transmission electron microscopy confirm body-centered cubic FeCo cores encapsulated by a continuous carbon shell. After annealing at 400 °C, the sample achieves a saturation magnetization of 240 emu g⁻¹ and a specific absorption rate (SAR, a measure of heating efficiency) of 191.5 W g⁻¹ at 300 kHz and 325 Oe. Higher annealing temperatures increase graphitization and coarsening and reduce both saturation magnetization and SAR. Optimum performance at 400 °C is attributed to oxidation-limiting shells of near-optimal thickness. These results identify graphitic carbon–coated FeCo nanocrystals as a promising platform for magnetic hyperthermia. Although ethanol is nonphysiological, it was used to benchmark intrinsic heating capacity; biocompatibility and colloidal stability in aqueous media will be addressed in future work.