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A paper in PNAS by an international scientific collaboration from the UK, Germany and Switzerland is the 7000th to be published as a result of innovative research conducted at Diamond Light Source, the UK’s Synchrotron. This new paper reveals details of the 3D spin structure of magnetic skyrmions, and will be of key importance for storing digital information in the development of next-generation devices based on spintronics.
Laurent Chapon, Diamond’s Physical Sciences Director, explains the significance of these new findings: "A skyrmion is similar to a nanoscale magnetic vortex, made from twisted magnetic spins, but with a non-trivial topology that is ‘protecting them’. They are therefore stable, able to move, deform and interact with their environment without breaking up, which makes them very promising candidates for digital information storage in next-generation devices. For years, scientists have been trying to understand the underlying physical mechanisms that stabilise magnetic skyrmions, usually treating them as 2D objects. However, with its unique facilities and ultra-bright light, Diamond has provided researchers the tools to study skyrmions in 3D revealing significant new data."
As spintronic devices rely on effects that occur in the surface layers of materials, the team was investigating the influence of surfaces on the twisted spin structure. It is commonly assumed that surface effects only modify the properties of stable materials within the top few atomic layers, and investigating 3D magnetic structures is a challenging task. However, using the powerful circularly polarised light produced at Diamond, the researchers were able to use resonant elastic X-ray scattering (REXS) to reconstruct the full 3D spin structure of a skyrmion below the surface of Cu2OSeO3.
Their research reveals that surface effects cause subtle changes in the properties of the material at depths of up to several hundred atomic layers. According to Dr Shilei Zhang, the team leader,
This has far-reaching implications for the creation of skyrmions in surface-dominated systems and identifies, more generally, surface-induced gradual variations deep within a bulk material and their impact on tailored functionalities as an unchartered scientific territory.”
The results suggest that the importance of free surfaces has been severely underestimated and will be of central importance for future skyrmionics applications. There is also a large discrepancy between the reconstructed experimental model and theoretical predictions, suggesting there is some underlying physics still to be explored.
Chapon adds: "Diamond’s 7000th publication exemplifies the links between fundamental research, applied science and the technologies that move humanity forwards. Discovery may be an everyday occurrence here at Diamond, but it never loses its shine.”
Video 1: Demonstration that the helicity angle of a skyrmion is an extra degree of freedom that can take arbitrary values. Most importantly, the helicity angle and its associated CD-REXS pattern have a one-to-one correspondence, described by the dichroism extinction rule. This lays the foundation for the experimental determination of the helicity angle in a real material.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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