Tuning the Curie Temperature of Fe₃O₄ to Achieve Automated Magnetic Hyperthermia

We examine the impact of samarium doping on the Curie temperature (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i>) of magnetite through density functional theory (DFT) calculations. Upon calculating the total energies of the different spin orientations among the cations in Fe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>: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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> 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 (Fe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>:Sm) has a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> 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<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> and 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> almost nearly preserves the Hall coefficient (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_H</i>), implying that Fe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>:Sm can be synthesized without significantly altering magnetite’s ability for tumor tissue identification based on the Hall effect.