Spinterface Engineering for Efficient Device Operation (SPEEDO)

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.

Spintronics is the most active research area currently being pursued worldwide in the field of magnetism, evidenced through representative papers at the leading magnetism conferences (MMM, Intermag, and JEMS) and the level of industrial and institutional funding (it is already a multibillion-dollar industry). Molecular spintronics is a subfield that has emerged more recently but also has enormous potential. One only has to look at the success of the related field of organic electronics, which has led to such device technologies as flexible OLED flat-panel displays and is now an industry also worth billions of dollars per year, to get an idea of the impact this field could have on the economy, society, and science base of the U.K.

The above successes have been built on decades of fundamental physical science research, most notably leading to the award of the Novel Prize for Physics to Albert Fert and Peter Grünberg "for the discovery of Giant Magnetoresistance'. The read-heads of all modern hard drives are based on spintronic principles of magnetoresistance, as are MRAM elements which have moved into the second-generation through the use of thermally-assisted switching and spin transfer torque. The massive increase in data storage, speed-of-access and display quality that these technologies have enabled have clearly led to a huge impact on the society and economy of the U.K., bringing benefits at both an individual and institutional level.

Although at a much earlier stage, organic spintronics also has significant promise in delivering real-world applications such as improved electronic devices and flexible memory elements. For this to happen, a much clearer understanding of the interplay between fundamental material properties and device performance is needed and this is where the proposed project will have the biggest scientific impact. Studying and optimising the interfaces that are central to the performance of an organic device will ultimately lead to faster, more efficient, and low-power operation. Already, it has been demonstrated that using a spin-polarised current in an organic light-emitting diode (OLED) leads to an increase in light-generation efficiency and a consequent saving in power. Further improvements in device efficiency based on a better understanding of material properties, coupled with the low-cost production methods of organic semiconductors, will ultimately lead to environmental benefits to U.K and a 'greener' society.

As a burgeoning field, there is a lot of potential to commercialise and exploit the scientific knowledge generated as a result of the fundamental research taking place in organic spintronics. For example, if the device fabrication concept proposed in this project works as as expected, it will lead to patentable technology. In the medium-to-long term, it is highly possible that spin-out companies will be developed, creating jobs and wealth. Much of the success of the organic electronics industry can be attributed to fundamental research conducted in the U.K., for example, at world-leading groups at Imperial College London and Cambridge University. This led to the creation of Cambridge Display Technologies, a spin-out company that was floated on the NASDAQ stock exchange in 2004 for $230 million.

Larger, multinational magnetism companies such as Seagate Technologies, whose European operations are based in Londonderry, will also benefit from a better understanding of the materials and processes they incorporate into their products. In turn, this will lead to increased R&D investment. For example, HGST (formerly Hitachi Global Storage Technologies) are investing in significant R&D resources to develop an organic spin transistor. Looking to more blue skies research, single molecule magnets are currently being explored as potential pathways to quantum technologies with simple qubit operations already demonstrated in the TbPc2 molecules that are involved in this proposal.