中子小角散射关联矩的磁结构因子
The magnetic structure factor of correlated moments in small-angle neutron scattering
摘要：
纳米结构磁性材料的结构和磁性之间的相互作用允许实现非常规的磁效应，这导致需要实验技术来确定具有纳米级分辨率的磁化曲线。磁性小角中子散射（SANS）探测化学和磁性纳米结构，因此是一种强大的技术，例如用于表征磁性纳米颗粒。在这里，我们表明，传统上使用的粒子矩阵的方法来描述SANS的磁性粒子组件，但是，导致一个有缺陷的解释。作为补救措施，我们提供了一般表达式的场依赖的2D磁SANS截面的相关时刻。结果表明，结构无序的合奏的磁结构因子是在一般情况下，与常见的假设相反，（i）各向异性也在零场，（ii），即使在饱和的磁结构因子偏离核的。这些理论预测定性解释了有趣的实验，极化SANS数据的偶极耦合氧化铁纳米粒子的合奏。
英文摘要：
The interplay between structural and magnetic properties of nanostructured magnetic materials allows to realize unconventional magnetic effects, which results in a demand for experimental techniques to determine the magnetization profile with nanoscale resolution. Magnetic small-angle neutron scattering (SANS) probes both the chemical and magnetic nanostructure and is thus a powerful technique e.g. for the characterization of magnetic nanoparticles. Here, we show that the conventionally used particle-matrix approach to describe SANS of magnetic particle assemblies, however, leads to a flawed interpretation. As remedy, we provide general expressions for the field-dependent 2D magnetic SANS cross-section of correlated moments. It is shown that for structurally disordered ensembles the magnetic structure factor is in general, and contrary to common assumptions, (i) anisotropic also in zero field, and (ii) that even in saturation the magnetic structure factor deviates from the nuclear one. These theoretical predictions explain qualitatively the intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled iron oxide nanoparticles.
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