Metal oxides: building blocks for future nanoelectronics
We human beings breathe oxygen to live. But oxygen is also part of a class of materials - transition metal oxides - which have excited academics and industry alike. Little is understood of their properties. EU-funded researchers, led by Trinity College Dublin, are keen to change that. The team has developed modelling tools for investigating the behaviour of potential micro- and nanoelectronic devices using transition metal oxides.
Described as outstanding building materials for future nanoelectronics, transition metal oxides possess a number of fascinating properties, including one overriding quality called ‘colossal magneto-resistance’ where the resistance changes in a magnetic field. In some of them – a class of multiferroic oxides – the path of electrical currents passing through an object can be altered by introducing an external magnetic field.
Developments in this field pave the way for countless practical applications, from new signalling operations in multifunctional devices to new memory sources in ultra-powerful computers, and devices that never lose your data.
“Despite the huge amount of work already accomplished in this field, a deep and complete understanding of these materials and their interfaces is still lacking,” says Professor Stefano Sanvito of Trinity College Dublin’s School of Physics and the Centre for Research on Adaptive Nanostructures and Nanodevices. He led a joint research programme – the Athena project – between European and Indian scientists which focused on advanced theories for functional oxides and new routes to handle the devices of the future.
This gap in understanding is due both to the complexity inherent in the physics of strong-correlated electrons, he explains, and “an unquestionable lack of coordinated effort devoted to share, integrate and develop the most advanced and powerful computational techniques available”.
Athena set out to close the gap by fostering collaboration between experts in Austria, Italy, Ireland and India who pursued the most advanced methodologies for the theoretical study of strongly correlated phenomena in transition metal oxides.
But magneto-resistance is by no means a new field. In 1856, Irish inventor Lord Kelvin came up with the principle of ordinary magneto-resistance (OMR). The physics community built on Kelvin’s OMR foundations and eventually derived the classification for so-called ‘colossal magneto-resistance’ (CMR), which describes the ability of metals, such as perovskite oxide, to alter the resistance on a massive scale.
It was not until the end of the 20th century that this technology began to live up to its potential with new applications opening up in solid-state devices. In other words, the circuits and parts in devices like a smartphone are built from solid materials, and the electrons, or other charge carriers, are confined entirely within these materials.
European leaderships results in new models
The exciting and relatively new (emerging in the 1990s) field of ‘spintronics’, for example, exploits both the intrinsic spin of the electron and its associated ‘magnetic moment’ plus its fundamental electronic charge in solid-state devices. The Athena project has now built models explaining the underlying behaviour of metal-insulator phase changes and magneto-electronic interplay.
The branches of physics involved are intensely complex, which is why the Athena partners joined forces in the first place. Together, they have been able to tackle, by first principles, key functions and correlations of metal oxides as viable building blocks for better, faster and more reliable future micro- and nanoelectronic devices.
Thanks to the exchanges between students and experts from Europe and India, Athena has performed ground-breaking work on new oxide materials and their interfaces which, according to Prof. Sanvito, will have a tremendous impact on academic and industrial research.
“Our team has developed parameter-free modelling tools for investigating the behaviour of systems and devices using transition metal oxides. These solve directly the equations of quantum mechanics, allowing us to understand the properties of existing materials and predict those of new ones.”