Evidence of particle-particle interaction quenching in nanocomposite based on oleic acid-coated Fe3O4 nanoparticles after over-coating with essential oil extracted from Croton cajucara Benth

This study reports on the synthesis and characterization of oleic acid (OA)-coated Fe₃O₄ nanoparticles (Fe₃O₄@OA) and AO plus essential oil (EO)-coated Fe₃O₄ nanoparticles (Fe₃O₄@OA/EO). The EO was extracted from Croton cajucara Benth (CCB) leaves; a plant from the Brazilian Amazon region. Structural and morphological characterizations were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) images, respectively. Additionally, thermogravimetric analysis and magnetization measurements (hysteresis cycle, zero field-cooled-ZFC, field-cooled-FC, and AC susceptibility) were used to assess thermal and magnetic properties of the as-fabricated samples. Rietveld refinement of XRD pattern confirmed the formation of magnetite phase with no extra phases, whereas TEM images revealed spherically-shaped nanoparticles in the Fe₃O₄@OA and (Fe₃O₄@OA/EO) samples with a mean physical size of 8.5 nm and 10.1 nm, respectively. ZFC and FC curves revealed the occurrence of blocked/frozen state below the maximum peak (T_max) at ∼81 K and ∼40 K for the Fe₃O₄@OA and (Fe₃O₄@OA/EO) samples, respectively. Moreover, low-temperature AC susceptibility vs. T curves recorded in the range of 0.2-1000 Hz showed that the OA coating of the Fe₃O₄ nanoparticles leads to a spin-glass-like behavior credited to the strong particle-particle interactions; meanwhile, the double layer (AO + EO) coating of the Fe₃O₄ nanoparticles remarkably quenches the particle-particle interaction leading to a superparamagnetic-like behavior.