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

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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.