Diamond Annual Review 2023/24

34 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 Magneticmaterials Group Science Highlights More brain-like computers could cut IT energy costs The computing power needed to train and run artificial intelligence (AI) systems is colossal, and the energy requirements are staggering. Training the GPT-3 model behind ChatGPT, for example, required 355 years of single- processor computing time and consumed 284,000 kWh of energy. This is one example of a task that the human brain handles much more efficiently than a traditional computer, and researchers are investigating the potential of more brain-like (neuromorphic) computing methods that may prove to be more energy efficient. Physical reservoir computing is one such method, using the natural, complex responses of materials to perform challenging computations. Researchers from the University of Sheffield are investigating the use of magnetic metamaterials - structured at the nanoscale to exhibit complex and emergent properties - to perform such computations. The high-quality data the team collected at I06 allowed them to gain a fundamental understanding of how the material behaved and develop ways to input and output data that “tune” the system to give very different computational properties from the same device. After adding electrical contacts to the metamaterial to build an electrical device, the researchers used magnetic fields to input data and electrical resistances as the output, demonstrating state-of-the-art performance in diverse benchmarking computational tasks. Developing a reconfigurable device like this raises the question of what happens when several of them - tuned to express different properties - are networked together. The team, is also developing a single device with multiple inputs and outputs, and looking into more energy-efficient ways of driving the dynamic behaviour that don’t rely on large magnets. Another exciting area of research is the potential for using these magnetic materials as smart sensors. Vidamour, I.T. et al . DOI:10.1038/s42005-023-01352-4 Figure: Schematic diagram showing three different reservoir architectures (a–c), with differing methods for providing input data (red circles) into reservoir nodes (blue circles) and reading reservoir state as output (green circles). Communications Physics (Commun Phys) ISSN 2399- 3650 (online) (CC BY). Folding and unfolding of magnetic skyrmion strings in higher dimensions Magnetic skyrmions are a magnetically ordered phase with a vortex configuration. Because of the topological properties of the vortex structure, they are excellent information carriers for magnetic memory devices. In recent years, research has been focusing on reducing the size of magnetic skyrmions via material optimisation. For example, common skyrmions that can be used for magnetic memory are on the order of tens of nanometers in size. However, from a topological point of view, magnetic skyrmions are also “shrinkable”. As shown in the figure, in terms of their spatial distribution, the vector field distribution of a skyrmions is equivalent to the one-dimensional topological defect-string in string theory, and the origin of strings can be traced back to topological singularities - magnetic monopoles. If a skyrmion can be folded into a structure similar to a magnetic monopole, its footprint will be greatly reduced. The research team used the helical magnet-ferromagnetic multilayer heterojunction to achieve precise control of the skyrmion string length. It was shown that the limit of one-dimensional string shrinkage is the zero-length point floating at the material interface (as shown in the figure). The research team used the three-dimensional analytical capability of the synchrotron radiation-based technique of soft X-ray magnetic scattering at the RASOR end- station of beamline I10 at Diamond Light Source to directly observe the process of the skyrmion string being gradually folded into a topological singularity. Importantly, the folded information can be unfolded again to reveal the complete structure of the string and restore its original configuration and size through the reverse process. This discovery provides a new research idea for understanding the origin of topological magnetic structures and topological magnetic storage. Haonan, J . et al. DOI: 10.1021/acs.nanolett.3c01117 Figure: Illustration of the evolution of folding a skyrmion string into a monopole. So-called bobbers are stabilised in the near-interface region of the material. The terminating end resembles an emergent monopole configuration. If the penetration length of the bobber is reduced (by varying the temperature of the material), a pure monopole is emerging that floats on top of the chiral magnet.