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.
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