Understanding and developing spin-based emitters for improved far-infrared radiation sources

The unique way that light interacts with magnetic/non-magnetic metal ultra-thin films with thicknesses less than 1/5000th the width of a human hair has recently been shown to offer a route to producing novel sources of radiation with wavelengths that cover a wide range stretching from the mid- to far- infrared. This emission covers the THz region that lies between the microwave and the infra-red wavelengths of the electromagnetic spectrum; a wavelength range that remains difficult to cover, but has an enormous potential for a diverse range of applications. For example, THz radiation is particularly useful for security screening of people at airports due to its non-ionising properties, as well as for looking at the spectral fingerprints of materials including explosives, drugs and dust particles.

The atomic properties of interfaces are well known to be critical to the functionality of many technologically important devices, examples include spin-torque transfer magnetic random-access memory (STT-MRAM), the sensors and media used in hard disk drives and new, artificial multiferroics.

This project is focused on developing much needed understanding of how the emission process from ultra-thin magnetic structures depends on the material properties. By gaining understanding of how the underlying mechanisms are responsible for the emission process we will be able to demonstrate commercially-viable emitters. More specifically, the first emitters will be realised that operate without the need for an external magnetic field, overcoming the limitation this requirement currently imposes on the active emitting area and output energy.

THz radiation also provides a currently untapped approach to investigating spin-based devices. The knowledge gained in understanding the relationship between material properties and THz emission will prove invaluable in the design of spintronic devices being developed for the next generation of data storage devices. The overall goal is the development of sources of THz radiation that will have impact in a number of future application areas, in particular when looking at the spectral fingerprints of materials for detecting dangerous gases and dust particles which present serious health and safety concerns in areas such as the mining industry. Hence, the development of well-understood spin-based emitters would have a direct impact on UK economic success by enabling the development of new applications of THz radiation and spin-based devices that will add to the technological advancement of society.

The diverse array of new science that can be studied with an ultra-broadband terahertz-time-domain spectrometer will certainly result in a significant worldwide market for the spintronic emitters. The development of terahertz (THz) sources capable of emitting up to 30 THz is of great interest to TeraView Ltd., a world leader in the development and application of THz technologies, (see letter of support), particularly as this has the potential to open up new application areas for the technology. We will further explore the potential of these emitters in collaboration with Laser Quantum Ltd., a leading international manufacturer of terahertz spectrometers, starting with the hosting of meetings at their research facility (see letter of support). Spin-based emitters of ultra-broadband radiation also have the potential to enable new gas and particulate safety monitoring systems. There are half a million deaths globally each year as a result of work-related dust inhalation. The potential to develop a new approach to accurately monitor real-time dust levels offers the potential for significant societal impact in mitigating dust-related illnesses. Trolex, a leading global supplier to the mining industry, are keen to explore this potential (see letter of support).

In addition to the technological outputs from this project, the knowledge gained in understanding the material properties governing the emission of broadband radiation will ultimately benefit the development of spintronic devices by providing a new non-contact method of characterisation. Spin-based devices are currently being investigated for the next generation of computer memory. The success of this venture depends on a deeper understanding of fundamental spin interactions in materials. If we can understand and control the spin degree of freedom in materials the potential for this and the whole of spin-based electronics is enormous.

The post-doctoral research associate employed on this grant will benefit from thorough training in all aspects of the thin film growth, materials characterisation, and the utilisation of terahertz spectroscopic techniques. Furthermore, the chance to work in collaboration with leading academics and global manufacturers of state-of-the-art terahertz spectrometers and gas/particulate safety detectors, will provide a wealth of training opportunities, ranging from advanced experimental techniques to business awareness. This will greatly benefit their future career, be it in industry or academia.

To enhance the collaborative aspects of the project, a PhD student will be recruited and supervised across the schools involved (funded outside of this proposal), which will add to both the technical impact and the impact for early career researchers. We also expect to recruit between two and four masters (MPhys) students during the course of the project who will gain valuable training in THz physics and spintronics. The proposers are also closely involved with the NOWNANO Centre for Doctoral Training (CDT) and we will seek opportunities to realise additional impact for students in the CDT.