Diverging Geometric and Magnetic Size Distributions of Iron Oxide Nanocrystals
Diverging Geometric and Magnetic Size Distributions of Iron Oxide Nanocrystals
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DOI：
10.1021/jp203373f
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发表时间：
2011-08-04
影响因子：
3.7
通讯作者：
Erne, Ben H.
中科院分区：
文献类型：
--
作者：
Luigjes, Bob;Woudenberg, Suzanne M. C.;Erne, Ben H.
制备大小和形状均一的磁性纳米颗粒的一个重要原因是要保证均匀的磁性。然而，在这里，我们证明了具有几何尺寸的低多分散性的20 nm或更小的磁性氧化铁晶体仍然可以具有惊人的宽广的磁偶极矩分布。对结晶度接近完美、孪生缺陷或位错密度较高的纳米颗粒进行了比较研究。用电子显微镜和X射线衍射仪对样品的尺寸、形状和晶体缺陷进行了表征，并根据稀胶体分散体的磁化曲线确定了磁偶极矩。几何尺寸多分散度为3.5%、磁性尺寸多分散度为35%的球形颗粒由于晶格缺陷破坏了单畴磁自旋耦合，散度最大。这与通常的隐含假设形成了鲜明对比，即统一的大小和形状保证了单个粒子的明确磁性。
An important reason to prepare magnetic nanoparticles of uniform size and shape is to ensure uniform magnetic properties. However, here, we demonstrate that magnetic iron oxide crystals of 20 nm or less with a low polydispersity of the geometric size can nevertheless have a strikingly broad distribution of the magnetic dipole moment. A comparative study was performed on nanoparticles with near-perfect crystallinity, twinning defects, or a high density of dislocations. Size, shape, and crystal defects were characterized with electron microscopy and X-ray diffraction, and magnetic dipole moments were determined from magnetization curves of dilute colloidal dispersions. The largest divergence was found for spherical particles with 3.5% geometric size polydispersity and 35% magnetic size polydispersity due to crystal lattice defects that disrupt single-domain magnetic spin coupling. This is in stark contrast with the usual implicit assumption that uniform size and shape guarantee well-defined magnetic properties of the individual particles.