Artificial Spin Ice for Rewritable Magnonics

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The key physical concept of this project is that magnetic spin-waves, or their quanta magnons, can act as information carriers and be manipulated for information processing & computation. Conventional computers rely on physically moving particles (electrons), and vast amounts of energy are wasted by ohmic loss and heating induced by electronic transit, both within the logic devices and particularly between the separate logic and storage media. If current trends continue, computation will consume one third of global energy production by 2040, and consequently increasing computational energy efficiency is a critical challenge. Because magnets can transfer information from one device to the next without the exchange of any physical particles and have intrinsic passive data storage, 'magnonics' is in principle orders of magnitude more energy efficient than standard electronics & a promising route to aiding the global energy crisis.Magnets are used in memory devices as they passively retain information written into them (non-volatile). This project will enable creation of coupled arrays of nanomagnets that can be viewed as both memory and processor where novel circuits can be written and reprogrammed at will. Our ability to accomplish this exploits a technique which we have developed called All-Optical Magnetic Switching (AOMS), allowing controlled writing of any individual nanomagnet in the array with a low-power laser like a Blu-Ray player, plus world-leading expertise harnessing nanomagnetic arrays for spin-wave information processing - including world-first demonstration of magnonic neuromorphic computation in an array of interacting nanomagnets.Each ferromagnetic nanoisland stores a fixed average magnetization, but the magnetic moment is not completely static, instead precessing around the average direction at characteristic resonant frequencies in the microwave (GHz) range. For a single nanomagnet, the frequency is controlled by its size and shape in the same way that shortening a guitar string changes the note. Coupled arrays of nanomagnets have distinct spectral fingerprints and these can be used for readout of states. The magnonic resonances are also highly sensitive to the magnetic texture of each island, and one of our recent breakthroughs exploits this to prepare bistable vortex & macrospin islands exhibiting far greater functional magnonic flexibility versus conventional all-macrospin systems.It is already well established from simulations that the exact microstate of the array controls the resonant frequency of the magnons and that we can realise switches and transistor type devices for logic functions where the magnetic state controls whether magnons of a specific frequency can pass through or not. This project aims to integrate different functional elements and explore prototype magnonic components and circuits. It is highly adventurous, and there are many experimental challenges to overcome to realise fully magnonic computation. For example, a process called damping causes travelling spin waves to attenuate rapidly with both time and distance. This presents a challenge in terms of completing the full computation before information is lost, as well as representing a source of energy inefficiency - though it can be avoided using resonant 'standing wave' magnons with which our scheme also functions. Although it is straightforward to measure these 'standing wave' magnons in a large array, detecting travelling magnons in nanoscale device structures is at the edge of state-of-the-art capabilities. In this project we aim to develop and expand these capabilities, building on our expertise and establish fundamental understanding of the physics of coupling, synchronization, transmission, and loss between different magnonic crystal states, and deliver a fruitful playground to explore novel computation architectures.