The enhancement of nanoparticle’s magnetic properties with a suitable coating is the main tool to increase their potential as an effective candidate for applications in different areas, especially in biomedicine. In the work here reported, Fe₃O₄ nanoparticles coated with natural oils were synthesized by iron (III) acetylacetonate thermal decomposition and the effects of the coating on the magnetic properties of these particles have been investigated. The oils were extracted from three Amazon fruits seeds: açaí, ucuúba, and bacaba by CO₂ supercritical extraction process, and the relative percentage composition of fatty acids were determined by gas chromatography. A systematic study of crystalline, morphological, and magnetic properties revealed a saturation magnetization (Ms) enhancement and high values of the anisotropy constant for Fe₃O₄ samples when coated with açaí and ucuúba oils, which present a large percentage of saturated total fatty acid. Our results indicate that nanoparticles with sizes smaller than around 5 nm present Ms values as high as that found for bulk Fe₃O₄ and, consequently, much higher than Ms values for nanoparticles usually coated with oleic acid. The nuclear techniques neutron activation analysis and perturbed angular correlations were used to better characterize the nanoparticles.

用合适的涂层增强纳米颗粒的磁性能是增加其作为不同领域，特别是生物医学应用的有效候选者的潜力的主要工具。在本文报道的工作中，通过乙酰丙酮铁（III）热分解合成了涂覆有天然油的Fe ₃ O ₄纳米颗粒，并研究了涂层对这些颗粒的磁性的影响。这些油是通过CO ₂从三种亚马逊水果种子：açaí，ucuúba和bacaba中提取的气相色谱法测定超临界萃取过程中脂肪酸的相对百分含量。对晶体，形态和磁学性质的系统研究显示，当涂有阿萨伊和乌库巴油时，Fe ₃ O ₄样品的饱和磁化强度（Ms）增强，并且各向异性常数值较高，这代表了很大比例的饱和总脂肪酸。我们的结果表明，尺寸小于5 nm的纳米颗粒的Ms值与整体Fe ₃ O _4的Ms值一样高因此，比通常涂有油酸的纳米颗粒的Ms值高得多。核技术中子活化分析和扰动的角度相关性被用来更好地表征纳米颗粒。