Radical-Bridged Lanthanide Molecular Nanomagnets

Rare-earth metals such as neodymium, terbium and dysprosium have unusual and highly desirable magnetic properties; some of their alloys are amongst the strongest known permanent magnets. Rare earth magnets have widespread applications in a range of settings, including computer hard-disk drives. Magnetic materials are particularly important for computing because they provide the means by which digital information is transferred to, stored within, and read from an information storage unit. The storage unit typically consists of a collection of magnetic domains, where ordering occurs across dimensions of hundreds of nanometres. The size of the magnetic domain is crucial because it determines the amount of information that can be stored and processed.

One of the most important tasks facing society today is to find ways of dealing with so-called Big Data, the term used to describe digital information that occurs in vast amounts and is of an increasingly complex nature. Processing Big Data with conventional magnetic storage media will eventually prove to be impossible, hence the development of new information storage devices is the grand challenge. The key to success with this challenge is miniaturization, hence this project will develop a new generation of magnetic materials on the molecular scale, with dimensions of only a few nanometres.

The molecular materials with which this project is concerned are known as single-molecule magnets (SMMs). In contrast to traditional permanent magnets, SMMs are discrete molecular nano-magnets that retain magnetization in ways that do not rely on interactions across large distances, hence they offer unique properties that have been proposed as the basis of ultrahigh-density information technology, with processing at unprecedentedly fast speeds. SMMs have also been proposed as the working components of nano-scale molecular spintronic devices. The drawback with SMMs is that all examples function only at liquid-helium temperatures: this project will develop SMMs that function at more practical temperatures, which will introduce the possibility of developing prototype devices. More broadly, achieving the aims of this project will make an important contribution towards advancing the EPSRC Nanoscale Design of Functional Materials Grand Challenge.

The aims of the project will be achieved using innovative synthetic strategies based on molecular rare earth compounds in which the metal centres are linked by a series of novel magnetic organic groups. The key advance that will be enabled by this project will be with the magnetic organic linkers, which provide an innovative way of preventing the processes that otherwise switch off the magnetic memory of SMMs. An important feature of the molecular design process is the ability to change the magnetic properties at the atomic level by, for example, switching the atoms that connect the rare earth metals from phosphorus to arsenic, and from arsenic to other main group elements. Alternatively, a family of organic linkers with the capacity to change their magnetic moments via targeted chemical modifications have also been proposed, a strategy that will allow fine tuning of SMM properties. The experimental approach will be complemented by high-level theoretical calculations, which will provide detailed insight into the new SMMs and will provide a rational way of developing improved systems.

Ultimately, we will develop SMMs that function at temperatures that can be reached by cooling with liquid nitrogen. Such materials would represent a step-change in molecular nanomagnetism, and would result in tremendous impact across the scientific community, with the potential to make impact more widely in society.

Economic and societal impact
The current proposal addresses the EPSRC Grand Challenge Nanoscale Design of Functional Materials. Magnets containing rare-earth elements, such as the neodymium-iron-boride (NIB) magnets, are used in about 50% of computer hard disk drives to enable storage and retrieval of digital information. The amount of information that can be stored by a magnetic particle is determined by its size, which is about 1-100 microns in a modern computer. Single-molecule magnets (SMMs) are molecular objects that can also retain magnetization similar to a NIB magnet, but, because SMM 'particles' are about 1000 times smaller, they offer fundamentally new physics that has been proposed as the basis of ultrahigh-density information technology. SMMs have also been proposed as the qubits in quantum computers, hence SMM technology could allow information processing at unprecedentedly fast speeds: computations requiring months of conventional CPU time could take a few seconds with SMM technology: this would offer solutions to problems of global importance, and would have tremendous impact on society.
The drawback with SMMs is that all known systems function only at liquid-helium temperatures: if SMMs that function at practical temperatures could be developed, a prototype device would become a realistic prospect, and would provide an investment opportunity for UK plc. Here, there is an analogy with superconductivity, which was discovered in 1911 but was only reported above liquid nitrogen temperatures in 1987. Despite the limitations, superconductors are now manufactured on a commercial scale. The highest temperature at which hysteresis has been characterized in SMM is 14 K. Success with the PI's project would result in SMMs that function at much higher temperatures, bringing devices closer to reality and creating potential for impact through wealth creation. The impact of this technology on society - from individuals, to governments and UK business - could be immense.

Researcher training and education
The project will generate impact by providing highly skilled individuals for the UK workforce, and this will be ensured by considering the development of the PDRAs in terms of scientific training and general skills.
The PI's group works on projects dealing with alkali metals in organic synthesis, with transition metal chemistry for small-molecule activation, and with lanthanides in molecular magnetism. This diversity will give the postdocs an opportunity to develop as synthetic chemists. The postdocs will be trained in important analytical techniques that will be useful to them beyond the completion of the project, including X-ray crystallography and NMR spectroscopy. The postdocs appointed to the project will also be trained to use a SQUID magnetometer. The PI's previous collaborations in molecular magnetism have involved world-leading physicists and theoreticians, and the postdocs will interact with this network of collaborators to broaden their knowledge.
The U of M offers career planning courses for postdocs, which provide insight into possible pathways to jobs in government or industry, and to establishing independent academic careers. As a complement to this, the School of Chemistry runs careers workshops led by independent research fellows. The postdocs will engage with the RSC's Continuing Professional Development course, which will help them to demonstrate a commitment to maintaining high levels of professional competence. Completion of the RSC's CPD course will lead to the postdocs acquiring Chartered Chemist (CChem) status, which recognises "the experienced practising chemist who has demonstrated an in-depth knowledge of chemistry, significant personal achievements based upon chemistry, professionalism in the workplace and a commitment to maintaining technical expertise". This aspect of the project will make an important contribution to the UK's talent pipeline.