Magnetic Iron Oxide Nanoparticles: Reproducible Tuning of the Size and Nanosized-Dependent Composition, Defects, and Spin Canting
Magnetic Iron Oxide Nanoparticles: Reproducible Tuning of the Size and Nanosized-Dependent Composition, Defects, and Spin Canting
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DOI：
10.1021/jp411481p
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发表时间：
2014-02-20
影响因子：
3.7
通讯作者：
Begin-Colin, Sylvie
中科院分区：
文献类型：
--
作者：
Baaziz, Walid;Pichon, Benoit P.;Begin-Colin, Sylvie
通过改变铁前体（硬脂酸铁）在表面活性剂存在下在高沸点溶剂中的热分解的不同合成参数，获得了平均尺寸在4-28 nm范围内的氧化铁纳米颗粒（NPs）。合成参数影响纳米粒子的成核和生长步骤，通过修改硬脂酸铁的稳定性，取决于单体的形成和浓度，与LaMer模型一致。因此，发现反应时间和/或温度依赖的单体形成主要作为溶剂和配体性质的函数而变化。尺寸在5-20 nm范围内的纳米颗粒的结构和磁性表征证实，纳米颗粒的组成从小尺寸（通常为12 nm）的磁赤铁矿经由中间尺寸的扰动氧化态演变。研究发现，比块状磁铁矿和磁赤铁矿的饱和磁化强度值低的饱和磁化强度值与这种成分演变以及氧化缺陷、表面自旋倾斜和体积自旋倾斜的存在有关，这些都是纳米颗粒直径的函数。小纳米粒子主要表现为表面自旋倾斜。具有大尺寸的纳米颗粒显示M-s，这取决于它们的氧化壳厚度、缺陷和表面自旋倾斜。具有中间尺寸的纳米颗粒显示表面，特别是体积自旋倾斜，这是由于这些纳米颗粒中的扰动氧化态引起的无序结构。
Iron oxide nanoparticles (NPs) with average sizes in the range 4-28 nm have been obtained by varying different synthesis parameters of the thermal decomposition of an iron precursor (iron stearate) in the presence of surfactants in high boiling solvents. The synthesis parameters affect the NPs nucleation and growth steps, by modifying the stability of iron stearate on which depend the monomer formation and concentration, in agreement with the LaMer model. The monomer formation, which is reaction time and/or temperature dependent, is thus found to vary mainly as a function of the nature of solvents and ligands. The structural and magnetic characterizations of NPs with sizes in the range 5-20 nm confirm that the composition of NPs evolves from the maghemite for small sizes (typically 12 nm) via a perturbed oxidized state for intermediate sizes. The values of saturation magnetization lower than those of bulk magnetite and maghemite were found to be related to this composition evolution and to the presence of oxidation defects, surface spin canting and volume spin canting as a function of NPs diameter. Small NPs presented mainly a surface spin canting. NPs with large sizes display M-s which depends on their oxidized shell thickness, defects and surface spin canting. NPs with intermediate sizes display a surface and in particular a volume spin canting due to a disordered structure induced by a perturbed oxidation state in these NPs.