Diamond Concise Annual Review 2020/21

20 21 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 0 / 2 1 MagneticMaterials Group T he Magnetic Materials Group at Diamond Light Source uses and develops a range of polarised X-ray probes including Resonant Elastic X-ray scattering (REXS), PhotoEmission Electron Microscopy (PEEM), X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic X-ray Scattering (RIXS). Over the last year, our research community has gained fundamental insights into the electronic and magnetic degrees of freedomunderpinning the physical properties of a host ofmaterials using these probes. In this contribution, we present research demonstrating how PEEM can unveil the complex antiferromagnetic domain structure in CuMnAs thin films following intense pulsed electrical switching. We also present results reporting how soft X-ray scattering combined with soft X-ray imaging can reveal the tubular structure of magnetic Skyrmions in FeGe thin films. The versatility of high-resolution RIXS is showcased in a remarkable study of lithium- ion (Li-ion) battery cathodes, demonstrating how metal migration and molecular oxygen formation degrade the charge-discharge cycle. The results demonstrate how polarised X-rays can uncover a wealth of electronic and magnetic detail to aid the development of advanced materials in applications ranging from low-power consumption electronics to next-generation energy materials. Pioneering the use of antiferromagnets in computing The field of spin-based electronics (spintronics) is making huge strides in the development of computing and memory storage applications. Traditionally, the orientation of the magnetisation of ferromagnets has been intensively studied, but now researchers are turning additional attention to antiferromagnets due to their ultrafast dynamics, insensitivity to external magnetic fields and absence of magnetic stray fields. However, antiferromagnetism has been challenging to harness for applications. An international research team investigated the microscale antiferromagnetic order in copper manganese arsenide (CuMnAs) films. Use of PEEM on beamline I06 at Diamond Light Source enabled them to take images of the antiferromagnetic structures inmicroscaledevicestructures.Electricalcontactsonthesampleallowed them to probe the magnetic state before and after applying current pulses. The team showed that the electrical switching and relaxation behaviour they observed can potentially mimic the characteristics of biological neural networks, offering the potential to develop efficient and high-speed neuromorphic computing applications that mimic neuro-biological architectures present in the human nervous system. Because electronic and magnetoelastic fluctuations may accompany the strong magnetic disorder, charge and spin-sensitive imaging with higher spatial and temporal resolution may shed new light on the underlying physics of this effect. Kaspar Z. et al. DOI: 10.1038/s41928-020-00506-4 Understanding the role of magnetic skyrmion tubes in data storage Magnetic skyrmions are particles that can be found in some magnetic materials with exciting potential applications for data storage in electronic devices. Although skyrmions are typically portrayed as two-dimensional whirl-like objects, they have a vertical, tube-like structure. To date, this three-dimensional structure has not been observed and this would be important for understanding their stability in data storage. A European research team were able to acquire the first direct observations of magnetic skyrmion tubes. They used the I10 beamline at Diamond Light Source to perform magnetic diffraction measurements on skyrmion material ~100 nanometres thick. The beamline’s soft X-ray diffractometer, Reflectivity and Advanced Scattering fromOrdered Regimes (RASOR), allowed them to perform the experiment while controlling the temperature of the sample and applying external magnetic fields. These breakthrough results allowed them to acquire images of skyrmions’vertical structure at X-ray imaging beamlines at the SOLEIL and BESSY II synchrotron facilities. These new insights into the nanoscale mechanisms that govern the formation and destruction of skyrmions is a crucial step in ensuring that any data encoded in the form of skyrmions is not lost when any device is turned off. Birch M. T. et al. DOI: 10.1038/s41467-020-15474-8 Optimising the efficiency of lithium-ion batteries Lithium-rich cathode materials are being studied for the next generation of lithium-ion batteries as they potentially carry more charge than conventional cathodes. However, complex changes in crystal structure and a pronounced drop in voltage between the first charge and discharge (voltage hysteresis) could limit their use. Understanding the reversibility of these chemical processes is critical in determining how well a cathode material functions. Researchers from the University of Oxford and Diamond Light Source used the RIXS beamline (I21) to study the chemical changes to the oxide ions at different stages of the battery charge-discharge cycle. Using high-resolution RIXS, they detected underlying vibrational fine structure that showed the oxidised oxide ions to be molecular oxygen. These oxygen molecules are trapped within the charged cathode material, but they can be reduced back to oxide ions on discharge. However, this process takes place at a lower voltage, giving rise to the voltage hysteresis. With this increased knowledge, researchers can now devise strategies to suppress the release of oxygen, or prevent its formation, in next-generation lithium-ion batteries with higher energy density. Higher energy density batteries will extend the driving range of electric vehicles and increase the battery life of portable electronics between charges. House R. A. et al. DOI: 10.1038/s41560-020-00697-2