Targeting Molecular Magnetic Hysteresis at Liquid Nitrogen Temperatures

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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.