TERASWITCH - Towards low dissipation THz-induced switching of magnetic materials

Magnetisation switching between two stable bit states (1 and 0) is the key principle of modern-day storage technology. With the explosion in the number of "always connected" devices, and the consumer desire for multimedia and social media content, the volume of data being stored and processed globally has risen at an unprecedented rate, as evidenced by the number of new data centres being built (e.g. Facebook's new data centre in Singapore). The vast quantities of data being generated globally is leading to the emergence of new markets with companies exploiting and trading data in diverse ways - an EU estimate values the digital economy in Europe will be worth 739bn euros by 2020[1]. This growing demand for data storage poses several big questions: where is this volume of data going to be stored? How can the growing demand for data storage and processing be made compatible with the political and social imperative for energy responsibility and, ideally, carbon neutrality? It is estimated that 20% of the world's electricity demand will be used to power data centres by 2025[2], a figure that will undoubtedly grow, and therefore any technology that reduces the energy requirements of data processing and storage is of great national and international importance. This proposal concerns research into reducing the energy use involved in data storage and processing.

Magnetic hard disk drives still form most of the data storage at the server (and hence cloud) level due to their low cost per bit. However, the process of writing information in disk drives uses a relatively large amount of energy due to the magnetic field needed to toggle bits between the two states. Studies in ultrafast magnetization dynamics using femtosecond (1 femtosecond is one millionth of a billionth of a second) laser pulses have demonstrated that low-energy switching is possible, using orders of magnitude less energy. Switching in these studies occurs within two picoseconds (one picosecond is a thousandth of a billionth of a second) opening up the possibility of writing up to 10^12 (a million million) bits per second, one thousand times faster than conventional recording methods, an extremely attractive avenue to realise much faster and more responsive devices that requires research investment. However, the use of strong laser pulses often results in a large amount of heating and can excite a lot of non-linear dynamics. One possible solution to this is to use light at frequencies that are in the THz range with high intensities. Historically, it has been very difficult to generate such light pulses, but recent experimental developments have made this possible and the area of THz science in general has attracted significant attention over the past decade and more recently to control magnetism. Initial studies have shown that significantly lower amounts of energy are required to switch the magnetisation state than in conventional recording, which could revolutionise the way we store and process information. This proposal is aimed at developing these ideas with the goal of understanding the underlying physical processes and how we can engineer efficient, low energy control of magnetism. The work will be carried out alongside world-leading experimental groups to provide important validation and comparisons with theoretical work.

1 - https://ec.europa.eu/digital-single-market/en/news/final-results-european-data-market-study-measuring-size-and-trends-eu-data-economy

2 - https://data-economy.com/data-centres-world-will-consume-1-5-earths-power-2025/

The outlined project will form a first step towards realising a leading research activity that has the potential to deliver high impact research that will drive the next generation of high frequency, low-powered storage and data processing devices. The current high demand for online multimedia content, social networking and other cloud-based technologies is one of the many causes of rising energy demands. Whilst there has been a push globally to replace the burning of fossil fuels with cleaner energies, there is still a long way to go to ensure that CO2 levels are controlled to limit the effects of global warming. With the number of always connected devices set to increase, the amount of computing power and storage required will inevitably continue to rise, exasperating some of these issues. Hence, new ways of storing and processing information that use significantly less energy than current technologies would have a huge impact on this energy demand. This proposal will identify the physical mechanisms and material properties that give rise to low-energy THz switching. Such research has the potential to lead to large social, environmental and economic impacts. In the medium-to-long term, engagement with industry will be sought as a key pathway to impact through funded schemes such as regional Knowledge Transfer Partnerships and Industrial Strategy Challenge funds.

A key objective is to develop a strong research activity in the field of THz-induced dynamics that is capable of setting the agenda for ultrafast science in the coming years. By developing state-of-the-art theoretical models, the work proposed will have a strong impact on the research community by providing key insight into experimental and other theoretical works. There are currently no research groups working on theoretical modelling of THz-induced spin dynamics and, given the increasing interest in this field, this makes this proposal and the setting up of a research group and activity in this area, crucial and timely for the development of a competitive and much needed research presence in the UK. A joint workshop on ultrafast spin dynamics, with a dedicated session on THz dynamics, will be organised as part of the Current Research in Magnetism (CRIM) series, that is typically organised by the Institute of Physics Magnetism working group. The proposal of such a joint meeting is supported by the working group and will be an excellent opportunity to bring together UK academics working in the field to discuss future avenues of research. The coordinators of the EPSRC-funded EXTREMAG ultrafast time-resolved user facility will be invited to provide information and update the community on the capabilities and activities of the facility.

The staff working on this project will receive tailored training from the PI and Sheffield Hallam as well as through the knowledge transfer from the Scientific Computing Department at STFC Daresbury Laboratory. The training of a broad range of skills will enable the PhD student and PDRA to become independent researchers in their own right and have transferrable skills applicable to a highly technical industry or academia.

The project will involve software development that will be made publicly available. A further key goal for this activity is to initially develop a user base of scientists to use the developed code for modelling magnetisation dynamics with direct input from ab-initio calculations. The longer term goal is to develop an automated and highly accurate multiscale package capable of describing the equilibrium and dynamic properties of any magnetic material that could be applicable to many areas of magnetism research. One clear pathway to enable this is through the PI's membership of CCP-Magnetism and STFC's involvement in CCP9 (the UK's main network dealing with electronic structure theory), with organised schools/workshops and flagship proposals to develop the code capabilities.