Tailoring magnetic properties of spinel nanoparticles by silica coating: Importance of surfaces and interfaces

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Spinel nanoparticles have attracted increasing attention because of their potential applications in magnetic recording media, ferrofluids, and biomedical technology. By colloidal synthetic approaches for monodisperse magnetic spinel ferrite and silicacoated ferrite nanocrystals we tune the size of the ferrite core and the silica shell by varying the reaction parameters in the microemulsion system. This will allow us to study the effect of the core’s size and shell’s thickness on the magnetic properties as, e.g., the effective anisotropy and the superparamagnetic blocking temperature in a systematic way. A detailed magnetic characterisation of the particles will be performed by Mössbauer and x-ray absorption spectroscopy. Both techniques give the possibility to distinguish the magnetic atoms with different valencies (like, e.g., Fe3+ and Fe2+ in the inverse spinel Fe3O4) on different lattice sites. In addition, by x-ray absorption spectroscopy and its associated circular dichroism the spin and orbital moment will be separated which is crucial for the microscopic understanding of the important magnetic properties including magnetic anisotropy.