Tuning the Curie Temperature of Fe3O4 to Achieve Automated Magnetic Hyperthermia

We examine the impact of samarium doping on the Curie temperature ( $T_{c}$ ) of magnetite through density functional theory (DFT) calculations. Upon calculating the total energies of the different spin orientations among the cations in Fe 3O 4:Sm, we realized that the Sm atom prefers to substitute an Fe from the octahedral site with a spin opposing that of the atom it replaces. Our results show that Sm doping weakens the ferrimagnetic J coupling between the octahedral and tetrahedral Fe atoms. As a result, the normalized magnetization profile across a broad temperature range shows that the samarium-doped compound (Fe3O4:Sm) has a $T_{c}$ of approximately 319 K, which aligns well with the target range for self-regulated magnetic nanoparticle hyperthermia (MNH) applications. Furthermore, we demonstrated that Sm doping in magnetite with high electron concentrations of $10^{22} \mathrm{~cm}^{-3}$ and $10^{23} \mathrm{~cm}^{-3}$ almost nearly preserves the Hall coefficient ( $R_{H}$ ), implying that Fe3O4:Sm can be synthesized without significantly altering magnetite’s ability for tumor tissue identification based on the Hall effect.