Coherent spin waves for emerging nanoscale magnonic logic architectures

Information technology (IT) has penetrated all aspects of life in modern society. At the heart of IT are miniature devices that can process and store information in one or another form. Currently, the information is processed mainly within semiconductor based data architectures based on tiny "transistors". In contrast, long-term data storage is dominated by magnetic hard disk drives, within which the information is stored as direction of tiny "magnetic needles" the two opposite orientations of which represent "0" and "1" values in binary logics. However, the semiconductor industry is predicted to reach the limit of miniaturisation within the coming decade, while the energy consumption becomes increasingly important both for environmental concerns and to align with use in portable battery fed devices.
In this project, we aim to demonstrate a key component of a novel device for information technology, which has the potential to lead to combined data processing and storage on the same chip. This device will be based upon 'magnonics', in which wave-like perturbations of magnetisation ('spin waves') travel through and interact in patterned magnetic tracks ('waveguides') to perform operations. We propose to construct a spin wave source such that the wave properties of many such sources are linked; technically, this is known as 'coherence'. Our proposed spin wave source consists of a magnetic nanowire antenna placed across the waveguides. Microwave radiation will create magnetic oscillations in the antennae, which in turn will induce the spin waves in the nearby waveguides.
Spin waves are proposed as logic signal carriers, thereby assisting their seamless integration with existing and future magnetic data storage technologies. This integration of signal processing and storage within a single architecture promises reduced energy consumption and fast device operation. In addition, we will exploit how the spin waves interact with the magnetic configuration of the various components. The materials and geometry of the antennae and waveguides causes the magnetisation to prefer to lie along their length. However, opposite magnetisations can be engineered to meet within, say, the waveguide to create a transition region called a 'magnetic domain wall'. By selectively configuring the orientation of the magnetic waveguide and antennae, including incorporation of magnetic domain walls, we will be able to program the magnonic device functionalities. The magnetic materials we propose to use don't require power to retain their magnetisation (non-volatility), meaning our devices will store the configuration when powered off and, therefore, will be instantaneously bootable upon switch on. The multiple stable configurations of the magnetic components and associated multiple functionalities will also provide an opportunity for creating more complex devices that could replace several semiconductor transistors in conventional electronics. Apart from consumer electronics, the devices will be advantageous for use in aerospace, space and sub-marine technologies in which their non-volatility and resistance to radiation will allow vital weight and cost savings to be made.
The collaborative research programme will be conducted jointly by the Department of Materials Science and Engineering at the University of Sheffield and the College of Engineering, Mathematics and Physical Sciences at the University of Exeter. The Sheffield team will contribute to the project their internationally leading expertise in nanotechnology and manipulation of magnetic domain walls, while the Exeter team will contribute their world leading expertise in dynamical characterization and theoretical modelling of magnonic devices. By joining their forces together, the two teams will ensure that UK will remain at the forefront at the magnetic logic technology, in particular opening the new interdisciplinary field of domain wall magnonics.

On the time scales of the project duration, our research will have direct and obvious impact within its own interdisciplinary field of magnonics, including its Physics, Materials Science and Engineering sectors. The impacts of the proposed research within the more general magnetics and spintronics communities will also develop rather quickly, on the time scales of years, by way of supplying important information on the key underpinning physics. The research will reach out to other fields of study of waves of other nature, such as photonics, plasmonics, phononics, etc, on somewhat longer time scales, perhaps also a few years. The impact mechanism will mainly have the form of magnonics concepts adoptable within the said research fields. On a longer time scale of 3-6 years, a wider penetration of magnonics knowledge into the related photonics and plasmonics communities will take place, possibly leading to emergence of completely novel interdisciplinary paradigms of physical concepts and associated technologies, the impact of which is difficult to predict at this point. There is also the possibility of this work impacting the use of nanomagnets in medicine for radiotherapy, although this would probably only materialise on time scales of 10 years or greater; high frequency magnetic field excitation is used to heat magnetic particles within the human body and we aim to learn much about similar processes in magnetic antennae.
The proposal is centred on a new technological paradigm aiming to make a step change in the hardware underpinning information technology (IT). IT will therefore be the main vehicle through which our research will impact society and the economy, both in the UK and internationally. Indeed, the recent advances in IT, in particular including the proliferation of the use of internet and mobile network devices, have changed working practices, hobbies, healthcare, and the overall quality of life. As a result, IT benefits have become increasingly accessible to public, penetrating all layers of the society. In this context, our research will from the outset benefit wider IT research, also including via competition and collaboration with the semiconductor industry.
Our project will contribute to training of the personnel needed to drive the growth of Materials Physics and the IT sector within the UK. The postdoctoral researchers at Exeter and Sheffield will gain experience of the use and development of advanced fabrication, nano-manipulation and measurement techniques, the development and application of theoretical models implemented using the state of the art computational tools, and working within a distributed team where effective communication is required to deliver ambitious goals. These young researchers will develop a comprehensive capability for the conduct of independent research that will prepare them for permanent academic positions or employment within industry.
Finally, by strengthening the magnetics technology research base in the UK, the project will contribute to the development of the critical mass of the magnonics or more generally magnetic logic and data storage research in the UK. In longer term when the commercial applications of magnonics are born, this will prove important in the decision making with regard to the location of the key research and manufacturing businesses (ranging from start-ups to branches of the established transnational industrial giant, such as Hitachi or Seagate) to be set up, hopefully within the UK or perhaps in the EU.