Spinterface Engineering for Efficient Device Operation (SPEEDO)

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Molecular spintronics is an emerging research field that seeks to build on the enormous successes of conventional spintronics (e.g. read-heads in all modern hard disk drives) and organic electronics (e.g. flexible displays) to produce devices such as organic spin transistors, flexible memory elements, and spin LEDs. Organic semiconducting molecules (OSCs) are mainly composed of light elements such as C, H, N, and O which means that they interact very weakly with an electron's spin--this is the fundamental property that spintronic technologies manipulate in addition to electronic charge. As such, OSCs are considered promising materials for use in devices in which it is desirable to pass spin-polarised electrons across an interface with a ferromagnetic material (spin injection) or to transport them from one ferromagnetic electrode to another (spin transport). Other beneficial properties of OSCs include their physical and chemical flexibility and the ability to produce them at low cost in large quantities.To overcome the poor and irreproducible performance demonstrated by first-generation organic devices, it has become increasingly clear that a much better understanding of the interaction between OSCs and the ferromagnetic substrates that support them is needed. The chemical interaction at this organic/ferromagnetic interface, or 'spinterface', can lead to undesirable effects such as molecular distortion, a reduction in spin polarisation, and the appearance of hybridised electronic states. The aim of this project is to provide this missing knowledge by using a beam of excited helium atoms as a very sensitive probe of surface electronic and magnetic properties. The surface sensitivity of this approach means that it is ideal for studying the adsorption of molecules on surfaces making its application to organic spintronics both novel and timely. In addition to common OSCs such as C60 and the metal phthalocyanines, more exotic 'double-decker' molecules that have a two-layer structure will also be investigated. Theory predicts that these molecules could act as very efficient spin filters however this needs confirming experimentally.The helium technique will also enable spinterfaces to be engineered with properties that are beneficial to device performance. For example, as we have shown before, the adsorption of simple atoms such as H and B can passivate the electronic states found at the surface of a ferromagnetic material such as Fe3O4 and recover desirable bulk properties such as half-metallicity. Based on these optimised spinterfaces, prototypical devices such as organic spin valves and magnetic tunnel junctions will be fabricated with the aim of demonstrating enhanced device performance. A novel method vacuum bonding process will also be developed to allow high-quality interfaces to be incorporated at both device electrodes. This opens up the possibility of preparing organic devices in which both the top and bottom electrodes consist of ferromagnetic oxides, a concept that has not been satisfactorily demonstrated to date.