Nanocrystalline metals and alloys - Cluster synthesis and tunable properties controlled by inter-facial charging

Project coordinator: Univ.-Prof. Dr. R. Würschum (Graz University of Technology)

The present projects aims at the cluster-synthesis of nanocrystalline metals and alloys and the control of their properties by electrical field-induced modifications of the charge carrier density in the interface region. The project will focus on charge-controlled magnetism, a topic from which a substantial added value to one main goal of the NFN, namely the development of novel kinds of nanophase magnetic materials, can be expected. The concept of charge-induced property tuning could be demonstrated recently by making use of nanocomposites of nanocrystalline metals and liquid electrolytes. Owing to the high surface-to-volume ratio of nanoscale metals, voltage-induced formation of electro-chemical double layers gives rise to a high fraction of interfacial space-charge regions which results in a reversible change of the overall physical properties of the metal.

Based on our recent pioneering studies on this topic, the project aims at an understanding of the microscopic processes which are relevant for charge-induced property tuning. Charge-induced variations of the magnetic properties are currently associated with a variety of effects, such as filling of electronic d-band upon charging, or charge-induced strain in combination with magneto-elastic coupling as well as charge-induced variation of magnetocrystalline anisotropy. Novel insight will be gained by comparative studies on selected model systems with strongly different magnetostrictive or magnetocrystalline behaviour as well as by comparative studies of magnetic properties and electrical conductivity in dependence of charging since charge-induced strain appear to affect magnetism and electrical conductivity to a different extent. Further goals will be the optimization of the charge-sensitivity of the properties and in particular the implementation of the concept of property-tuning to bulk solid-like materials. The project is closely linked with the NFN partners. Collaboration within the NFN will be essential for studying the tunable magnetic properties. In addition, the present project brings methods of cluster synthesis into the network which are complementary to the mechanical techniques. In cooperation with the NFN-partners, the technique of crystallite condensation in inert gas will be combined with subsequent high-pressure torsion (HPT) with the aim to prepare pore-free nanocrystalline metals with reduced crystallite size compared to conventional HPT-processing.