Micorstructural and magnetic characterisation of a new kind of magnetic hybrid materials

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Classical magnetic hybrid materials contain either magnetically soft or magnetically hard particles. Thus, they show either an active magnetorheological effect or exhibit passive magnetorheological properties after magnetization of the magnetically hard particles. Within the research association a mixture of magnetically hard and soft particles in an elastomeric matrix is expected to provide a combination of active and passive magnetorheological properties. In this context, it will be the central goal of the research association to synthesize tailored magnetic hybrid materials for sensor applications based on a detailed microscopic understanding of the material properties. Within the subproject described here, microstructural investigations as well as the experimental analysis of the magnetic interparticle interactions will be in focus of the working program. The microstructural investigations will use X-ray microtomography measurements allowing a three-dimensional evaluation of the particle distribution with single particle resolution. For this purpose tools for digital image analysis enabling an effective determination of the different particle species will have to be developed first. Afterwards the particle distribution and their change under influence of external stimuli like magnetic field and mechanical load will be analysed. The respective data will serve as well as an input as as a benchmark for the simulations undertaken by the theoretically working groups within the research association. Since the reorganisation of the microstructure is significantly determined by the magnetic interparticle interaction between the different particles, the second part of the subproject will focus on an experimental approach to the change of these interactions by changes of the composition of the magnetic hybrid material. Therefore First Order Reversal Curves (FORCs), i.e. partial hysteresis loops will be recorded. Preliminary investigations have shown that these data are sensitive for the composition of the magnetic hybrid materials and provide clear fingerprints of the internal magnetic interaction of the particles. A detailed interpretation of the data requires a deeper theoretical understanding of the curves, which will be provided by the theoretically working groups. In total, we expect that the project will provide detailed information about the relation between microstructural changes and macroscopic properties of the magnetic hybrid materials. This information will provide the basis for a prediction of certain material properties, which can be achieved by respective changes in composition of the material.