Iron oxide nanoparticles were synthesized by an original multistep seed-mediated growth approach. The thermal decomposition of an iron stearate precursor was performed successively up to 5 times to produce nanoparticles with a narrow size distribution from 6.4 to 15.0 nm. The chemical composition and crystal structure of each set of nanoparticles was characterized by TEM, FT-IR, XRD, and Mössbauer spectrometry. Each layer was successively grown at the surface of a pristine Fe_3-δO₄ nanoparticle by epitaxial relationship and resulted in a single crystal structure. An intermediate wash after each thermal decomposition step resulted in the surface oxidation of each layer. Therefore, the maghemite phase increased relative to the magnetite phase as the nanoparticle expanded. Finally, the study of the magnetic properties by SQUID magnetometry showed the trend of the magnetic anisotropy energy to increase as a function of the nanoparticle size. In contrast, the coercive field and the magnetization saturation display nonmonotonic variations that may result from the interplay of intrinsic and collective properties.

中文翻译：

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增加Fe的大小_-δ3 ö ₄纳米粒子通过进行多步种子介导的生长方法

通过原始的多步骤种子介导的生长方法合成了氧化铁纳米颗粒。连续进行硬脂酸铁前体的热分解多达5次，以生产具有从6.4到15.0 nm的窄尺寸分布的纳米粒子。通过TEM，FT-IR，XRD和Mössbauer光谱对每组纳米颗粒的化学组成和晶体结构进行了表征。每个层依次生长在原始的Fe的表面_3-δ Ò ₄纳米颗粒通过外延关系而产生单晶结构。每个热分解步骤之后的中间洗涤导致每个层的表面氧化。因此，随着纳米颗粒的膨胀，磁赤铁矿相相对于磁铁矿相增加。最后，通过SQUID磁力测定法进行的磁性能研究表明，磁各向异性能随纳米颗粒尺寸的增加而增加。相反，矫顽场和磁化饱和度显示非单调变化，这可能是由于固有特性和集合特性的相互作用所导致的。