We successfully synthesized and thoroughly characterized two series of magnetic nanoparticles vanadium and aluminum ferrites with average sizes ranging from 8 to 36 nm. These nanoparticles were obtained via the thermal decomposition of vanadium, aluminum, and iron acetylacetonates in the presence of oleic acid and oleylamine. Electron microscopy techniques, including SEM-EDS, TEM, and HRTEM, confirmed the expected stoichiometry and morphology: smaller particles were predominantly spherical, while larger ones exhibited faceted structures. Selected-area electron diffraction (SAED) patterns obtained from HRTEM images confirmed a face-centered cubic (FCC) spinel crystal structure across all samples. Compositional analysis by STEM-EELS revealed a core shell structure with a vanadium-rich shell in vanadium ferrite nanoparticles, whereas aluminum ferrite nanoparticles displayed a more homogeneous elemental distribution. These observations were further supported by X-ray photoelectron spectroscopy (XPS) performed on powder samples. Magnetic properties were assessed using SQUID magnetometry. Smaller particles exhibited superparamagnetic behavior below room temperature, while the largest particles showed a blocked regime extending up to room temperature. All samples demonstrated magnetic properties comparable to bulk magnetite, with effective anisotropy constants similar to or lower than bulk values, as determined through ferromagnetic resonance (FMR) experiments. These properties correlated well with heating efficiency, assessed via both calorimetry and AC magnetic hysteresis loop measurements, yielding specific loss power (SLP) values of up to 1000 W/g. Electron spin resonance (ESR) spectroscopy detected hydroxyl radical (•OH) concentrations as high as 2300 nM, indicating strong peroxidase-like activity in vanadium ferrite samples. In contrast, aluminum ferrites showed reduced activity, likely due to partial substitution of divalent iron ions by trivalent aluminum ions in the crystal lattice. The best-performing samples (15 and 30 nm) were successfully transferred into aqueous media using a glucose coating and incubated with pancreatic cancer cells for biological testing. TEM imaging confirmed efficient nanoparticle uptake, with localization in lysosomal and endosomal compartments. Cell viability remained above 100% at concentrations up to 100 µg/mL of magnetic nanoparticles. The effects of intracellular nanoparticle excitation by external stimuli such as alternating (AC) magnetic fields and near-infrared (NIR) laser irradiation are still under investigation. However, in some cases, loss of cell membrane integrity was observed via TEM in samples prepared by high-pressure freezing and freeze substitution, suggesting increased production of reactive oxygen species (ROS) potentially induced by nanoparticle excitation.
