EPSRC-SFI: Emergent Magnetism and Spin Interactions in Metallo-Molecular Interfaces

Lead Research Organisation: University of Leeds
Department Name: Physics and Astronomy

Abstract

The interface between two materials can be used to give rise to new properties that neither component could have separately (emergence), to tune the capabilities found in of one of them (enhancement), or to share functionalities (proximity). Our range of magnetic materials is limited; only the metals iron, nickel and cobalt show spontaneous magnetic ordering at room temperature. Here, we use molecular interfaces to generate novel magnets outside the Stoner criterion, to control the spin properties of thin films and add functionalities. From a fundamental point of view, the origin of these effects is not fully explained due to the complexity of the interfaces, the materials involved and their intricate quantum-electronic properties. The scientific plan of the proposal is:

i. To develop a new theoretical framework to study magneto-molecular coupling and interfaces accounting for the many physical factors at play in the coupling between metals and molecules. These factors include, possibly in combination, interface structure and relaxation, the degree of re-hybridisation and the ensuing charge-transfer for the emergence and descriptors of interfacial magnetic ordering.

ii. To improve the properties of commonly used magnetic thin films via nanocarbon overlayers. Magnetic materials play a critical role in computing, sensors, power conversion and generation, signal transfer and many other technologies. Tuning of the desired properties is achieved via alloying between 3d ferromagnets and/or other metals (e.g. FeNi, FeCoB), by combining with rare earths (e.g. SmCo and NdFeB), using high spin orbit coupling interfaces (e.g. Co/Pt) or using oxides to achieve insulating ferrimagnets (e.g. YIG). These strategies can lead to a wide range of magnetic anisotropies, coercivities and conductivities. However, some functionalities, such as the electric control of magnetism, the combination of semiconducting and magnetic properties or enhancing the blocking temperature in magnetic elements remain elusive. Furthermore, some of the materials used in magnetism and spintronics are expensive, harmful to the environment and/or difficult to recycle. Molecular interfaces, on the other hand, make use of abundant, eco-friendly materials to bring about new or enhanced spin functionalities. Such opportunities include the generation of spin ordering in dia/paramagnetic metals, the control of coercivity (soften/harden), increases in the ordering temperature of nanostructures, the manipulation of the magnetisation axis, and improved performance in spin torque devices by tuning the spin orbit coupling.

iii. To create the opportunity for switchable magnetism by turning on/off the interfacial spin ordering using electric fields. Fully stable spin ordering is required in applications such as magnetic memories. However, having the capability to turn on and off the magnetic response of a sample would open new avenues of research and applications, from future high frequency superconducting electronics and qubits, to the design of sub-wavelength photo-memories. The properties of metallo-molecular interfaces are highly dependent on charge transfer and re-hybridisation. Electric or optical irradiation can therefore be used to control their magnetic response.

The consequences of spin ordering and polarised electron transfer are not limited to magnetic materials and their usage. Charge transfer is an essential chemical and biochemical process, and research in spin-related metallo-molecular coupling can also in the future contribute to other areas of science, such as electrochemical energy storage, electro-catalysis, and the use of metals in biomedical applications such as medical imaging.

Planned Impact

Our previous research demonstrated that the established premise that iron, cobalt and nickel are the only elements showing spontaneous magnetic ordering at room temperature can be beaten by using molecular interfaces. Although these three elements, plus their alloys, combinations and compounds fulfil a wide range of needs, the possibility of bringing a new class of magnets, with new functionalities and physico-chemical properties are the very exciting prospects that we bring here. However, our focus for the duration of the grant remains into basic research and understanding of this new phenomenon. The reach of this research has enormous potential, as demonstrated by the publication of the original results in a number of scientific dissemination magazines (Cosmos Magazine, Discovery Magazine), scientific websites (Physics Today, Nanowerc etc.) and blogs (IFL Science) that attracted tens of thousands of reads and thousands of comments from people all over the world.

From an economic point of view, there is a large number of companies in the UK, Ireland and elsewhere that depend on magnetic materials for computing (e.g. Seagate, Hitachi), in addition to small companies working on sensors, molecular electronics (e.g. Cambridge Display Technology), power conversion etc. It is estimated that 10% of the world's electricity in 2013 was used in ICT -with this number growing 3 times faster than the average electricity consumption between 2007 and 2012, although alternative strategies in data management have damped the most pessimistic predictions of the past. Approximately 80% is wasted in heat. Although our grant is focused in oriented basic research and fundamental understanding, this needs to be the first step towards new architectures where eco-friendly materials, low-power dissipation and versatility dominate technological goals.

The Irish-UK partnership represents an ideal complementary matching of capabilities that will maximise the benefits of resources from both countries towards an optimum output. Nanoscience and nanomaterials are essential to research in electronics, biophysics, polymer science and energy amongst others. The eventual impacts are far-reaching: for instance, the development of magnetic nanomaterials has allowed vast quantities of cheap data storage that underpin the internet and communications revolution, which has massively accelerated with ubiquitous mobile devices requiring access to cloud-based services (i.e. underpinned by magnetic memories and sensors).

From the point of view of outreach to the general public, magnetism and nanotechnology are fields that attract the imagination of students and people of all ages, particularly in terms of unusual emergent quantum phenomena and their applications to everyday appliances. In this regard, our research will provide examples of how fundamental, but application-motivated studies in many different areas can have impact on, and be impacted by, an advanced technology that is evermore present in most aspects of our lives. Opportunities for public engagement we can include outreach to schools (through Leads' 'Physics in Schools' module and TCD's Transition-Year Physics Experience, for instance), scientific workshops (e.g. Pint of Science) or council activities (e.g. Leeds Science Festival).

Another focus of the project is in career development and scientific transfer. The broad range, state-of-the-art physical and computational techniques involved, the close relationship between theory and experiments, and the novelty of the research will further increase the desirability of employment for the early career researchers hired throughout the project, while fostering the UK and Ireland's expertise in materials physics and technology.

Publications

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