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Final Activity Report Summary - SYNTORBMAG (Synthesis an Orbital magnetism of core-shell nanoparticles)

Monodisperse magnetic nanoparticles, ranging at size from 3 to 200 nm, have a huge potential for medicine applications, such as tumour therapy, gene sequencing, contrast agents in magnetic imaging, bio-labelling or drug delivery agents, as well as in information technology relevant areas, e.g. non-volatile data storage and sensor applications. Most of the magnetic nanoparticles have the disadvantage of either being bio-incompatible or thermally unstable due to very low magnetic anisotropy energy.

The goal of the network was to synthesise and characterise new types of core shell particles, in the size range between 3 and 200 nm, consisting of a magnetic core with a large magnetic anisotropy, e.g. FePt or CoSm, which would be protected by an inert, bio-compatible shell of few atomic layers of noble metals, namely silver (Au), gold (Ag) and platinum (Pt), or iron oxides. Atomic layer control over the shell thickness and the core diameter was achieved. The new combination of ferromagnetic core (three-dimensional metal) and ferrimagnetic shell materials, e.g. 4f metals or oxides, yielded high coercive nanoparticles which could be used as building blocks for novel magnetic materials. The complex interface and surface magnetism of individual nanoparticles which were unique in terms of their high surface to volume and interface to volume ratio, ranging from 0.2 to 0.5, were investigated by ferro-paramagnetic resonance and magnetic circular dichroism, which allowed for the determination of element specific magnetic moments and the distinction of orbital contributions from the core, the interfaces or the surface.

The results of this basic research allowed for a better understanding of the functionalisation of the interface properties which controlled the response of magnetic sensors exchange bias or the compatibility to medical applications. The added benefit for the participating researchers was the interdisciplinary training in organochemical synthesis of complex nanoparticles and the work at large synchrotron user facilities exploiting unique magnetic and chemical characterisation techniques.

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