Microscopic understanding of particle-matrix interaction in magnetic hybrid materials by elementspecific spectroscopy

对磁性混合材料在工作条件下的行为的理解还不完善。特别是在嵌入的纳米颗粒的局部尺度上，外部磁场对布朗运动、取向和颗粒与周围基质材料的耦合的影响还没有得到充分的理解。为了详细研究纳米级磁性复合材料的这些特性，计划在该项目的范围内利用同步加速器设施的穆斯堡尔谱、交流阻抗测量和X射线吸收光谱来研究含有磁性纳米颗粒的不同（粘）弹性介质。从穆斯堡尔吸收线的加宽和形状可以得到关于内尔弛豫和布朗粒子运动的信息。这提供了新的见解，在受约束的颗粒的流动性取决于周围的纳米结构的个别基质材料和在不同的外部磁场的两个弛豫过程的可能的变化。此外，嵌入颗粒的取向以及自旋结构可以从穆斯堡尔吸收线的强度分布确定。这些实验的结果应通过使用X射线吸收光谱和X射线圆二色性分析元素特定的电子结构来证实，并提供有关颗粒-基质界面磁性的信息。X射线吸收光谱以及穆斯堡尔谱可以在强磁场中获得，从而在工作条件下获得关于粒子-基体相互作用的有价值的信息。一个更详细的研究布朗粒子动力学计划进行互补测量的磁性交流磁化率。在这个项目中实现的微观理解将有助于通过将这些信息传递给合成系统的小组来产生杂化材料的新功能。

The understanding of the behavior of magnetic hybrid materials under working conditions is still imperfect. Especially on the local scale of the embedded nanoparticles the influence of external magnetic fields on Brownian movement, orientation and the coupling of the particles to the surrounding matrix material is not sufficiently understood. To investigate these properties of magnetic composite materials on the nanoscale in detail, the study of different (visco-) elastic media containing magnetic nanoparticles is planned in the scope of this project utilizing Mössbauer spectroscopy, AC-susceptometry and X-ray absorption spectroscopy at synchrotron facilities. Information on Néel relaxation as well as on Brownian particle motion can be obtained from the broadening and shape of the Mössbauer absorption lines. This provides new insights in the constrained particle mobility depending on the surrounding nanostructure of the individual matrix material and on possible variations of both relaxation processes at different external magnetic fields. Additionally, the orientation as well as the spin structure of the embedded particles can be determined from the intensity distribution of Mössbauer absorption lines. Findings from these experiments shall be substantiated by analyzing the element-specific electronic structure using X-ray absorption spectroscopy and X-ray circular dichroism, providing information on the magnetic properties of the particle-matrix interface. X-ray absorption spectra as well as Mössbauer spectra can be obtained in strong magnetic fields, yielding valuable information on the particle-matrix interaction under working conditions. A more detailed study of Brownian particle dynamics is planned by performing complementary measurements of the magnetic AC-susceptibility. The microscopic understanding achieved in this project will help to generate new functionalities of the hybrid materials by transferring this information to the groups synthesizing the systems.