Tunable Control of the Structural Features and Related Physical Properties of Mn_xFe_{3- x}O₄Nanoparticles: Implication on Their Heating Performance by Magnetic Hyperthermia

Four different manganese ferrite (Mn_xFe_3-xO₄) nanostructures (9 and 15 nm spheres (S1, S2), 18 nm nanoflowers (NFs), and 20 nm cubes (NC)) were prepared in this work through a thermal decomposition method by tuning the critical synthetic parameters. In all of the prepared materials, the cation composition of the ferrite phase was rather similar. The occurrence of a secondary phase of mangano-wüstite within Mn_xFe_3-xO₄nanoparticles and its impact on the magnetic properties were studied in detail from static and dynamic magnetic measurements complemented with Mössbauer spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) analysis, and X-ray photoelectron spectroscopy (XPS). All of the computed data were consistent with a deterioration of the magnetic output as the reduced phase becomes progressively important, leading to a marked spin disorder and the reduction of either the effective magnetic size or the saturation magnetization. The heating efficiency was measured from 100 up to 300 kHz and from 8 up to 24 kA/m, the NF sample being the one displaying the highest specific absorption rate (SAR) under all tested conditions. These results agreed with the physicochemical and magnetic characterization of the particles, highlighting the interest of the detailed characterization of the particles to understand their heating properties relevant for biomedical applications and others such as catalysis.