Targeting Molecular Magnetic Hysteresis at Liquid Nitrogen Temperatures

For over fifty years economic factors have driven a steady trend of making electronic devices smaller. However, the rate of progress in miniaturisation has started to stall, and it has been predicted that a plateau may be reached within ten years. As such, "bottom-up" alternatives are sought to rival the current "top-down" approach to ensure continued technological advancement. One promising solution for high-density data storage is to use Single Molecule Magnets (SMMs). These are molecules that can store magnetic information, and could therefore give the smallest possible devices.

Lanthanide (Ln) SMMs have emerged as leading candidates due to their favourable magnetic properties, but at present these only function with expensive liquid helium cooling. The highest temperature at which Ln SMMs retain magnetic information is dictated by the choice of Ln, the atoms bonded to the Ln and the resultant molecular geometry, and the competition of magnetic relaxation pathways. These factors can all potentially be controlled but at present the relaxation mechanisms are still poorly understood. Efficient relaxation processes can significantly lower the temperature at which magnetic information is retained, based on what would be predicted solely from consideration of an isolated Ln SMM, and thus these must be investigated to make progress.

We have recently found that Ln cations bonded only to two five-membered carbon atom rings in an axial arrangement give a SMM for which the highest temperatures at which magnetic hysteresis, a memory effect that is essential for data storage, has ever been observed. As such, we target the syntheses of more complex Ln SMM structures based upon this motif to provide even higher hysteresis temperatures. These systems could operate above liquid nitrogen temperatures, at which point they would become technologically viable. The magnetic relaxation pathways of these systems can be studied in depth over a large temperature range. This will allow us to deepen our understanding of the factors governing relaxation mechanisms, so that in future we can design Ln SMMs that disfavour such processes and can store magnetic information at even higher temperatures.

In recent work (Nature, 2017, 548, 439), we have used our Ln SMM design criteria to report by far the largest molecular hysteresis temperature reported to date (60 K). This is the single biggest leap in nearly 25 years (the previous record, 14 K, was set in 2011; 4 K was the initial achievement in 1993) and is now only 17 K away from operation under an economically viable liquid nitrogen regime. We have made theoretical predictions for improvements to the design of this system to raise the hysteresis temperature even further by modifying the carbon atom rings, and have set out synthetic routes to achieve this goal in this proposal. More ambitiously, we target the synthesis of "triple decker" compounds that contain two dysprosium cations and three small carbon atom rings in an approximately cylindrical arrangement. Ln ions prefer high coordination numbers, hence the synthesis of triple decker complexes containing only five-membered carbon atom rings would be a remarkable synthetic achievement.

All synthetic studies in this proposal will be complemented by high level physical analysis of magnetic and electronic properties, including computational modelling. This will provide essential information to guide our pioneering studies of magnetic relaxation pathways and their relationship to the geometry and electronic structure of Ln SMMs. Ideally we may synthesise a Ln SMM that can operate at liquid nitrogen temperatures.

The PI and CI have strong track records in delivering impact through their outputs, and have established significant collaborations. We align with key EPSRC themes and priority areas and we will deliver:

1. A deeper understanding of f-element chemistry and magnetic relaxation pathways.
2. Results that are of both academic and future technological benefit.
3. Early career researchers with a unique sets of skills that benefit the UK economy.
4. Significant outreach activities to communicate this work to the public.

The Pathways to Impact document describes our strategy to maximise the impact of our work on economy, society, knowledge and people. We use a variety of activities to engage with the public and private sectors, academia and the public, with well-defined timescales and milestones set out in a Gantt chart. Our impact strategy beyond academia is summarised here,

Outreach: The PI has a proven track record of public outreach activities. For example, the PI has received formal outreach training and delivered live experiments at schools and a series of public lectures at the 2012 Royal Society Summer Science Exhibition. They have also been a consultant for BBC Worldwide, contributed to the Nuclear Hitchhiker blog and engaged with A-level students at the British Science Foundation Science Journalism Contest 2017. We will build on these activities during this project by setting up dedicated f-element stands at the annual Manchester Science Festival and Bluedot, and building new web content to further publicise this work. Our group members will also be involved in regular outreach activities organised by the School of Chemistry involving schools and sixth-form colleges, including lectures, workshops and laboratory classes to engage a considerable number of pupils, teachers and parents.

Industry and Commerce: In a best case scenario we could access single molecule magnets (SMMs) that can store data at liquid nitrogen temperatures. This would make SMM storage devices technologically viable for the first time. Although potential economic impact is expected outside the timescale of this grant application, mechanisms are already in place at Manchester to achieve this, including industrial knowledge transfer partnerships. The University of Manchester Intellectual Property Company (UMIP) provides a free and easy to access service to discuss potential commercialisation opportunities at an early stage of development. Following identification of commercial potential, UMIP can provide proof-of-concept funding to allow a short-term PDRA (e.g. 6-12 months) to shape potential industrial scale-up and patent applications. Following intellectual property protection, UMIP will assist with marketing products to industry.

Training: The PDRA will be part of a multidisciplinary team involving two research groups. As such they will receive skills and training that are unique to this project that will give them an excellent foundation upon which to build their future careers. They will gain the rare ability to handle highly air sensitive f-element complexes, recently highlighted as a major skills shortage by government and the nuclear and fine chemical industries. They will also gain insight in the analysis and interpretation of f-element magnetic and spectroscopic data, coupled with high level ab initio calculations. These proficiencies would also be of use for the nuclear industry for the modelling of waste streams and internuclear separations. The PDRA will be actively encouraged to design and to implement their own strands of research and to prepare manuscripts for publication to give them the best possible chance of success in pursuing a career in academia or in industry. Transferable and general skills will also be developed in tandem to make group members highly employable in other career paths.