Diamond Concise Annual Review 2019/20

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 1 9 / 2 0 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 1 9 / 2 0 18 19 MagneticMaterials Group T heMagneticMaterials Group focuses onwork at the frontiers of condensedmatter physics, materials science and engineering ranging from topological states of matter, superconductivity, spintronics (the study of electron spinning and associated magnetism in solid state devices), two-dimensional systems, skyrmions (particles that may provide new forms of data storage) and multiferroics. The Group uses a diverse range of sensitive polarised X-ray probes including resonant X-ray scattering, PhotoEmission Electron Microscopy (PEEM), X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic X-ray Scattering (RIXS) on beamlines I06, I10, I16 and I21 to tackle a variety of challenges and opportunities in exploiting the changes inmagnetic properties of materials. Studies this year have included early development of new information technologies using 3D topological insulators, designing new high- temperature superconductors, and improving the energy efficiency of electronic devices utilising the piezoelectric properties of materials. Developing new information technologies Three-dimensional topological insulators (TIs) are nonmagnetic insulators that show novel phases of quantum matter and sharp transitions in the electronic structure near their surfaces. They have potential uses for next-generation energy-efficient electronics. Although the metallic surface states of TIs have been extensively studied, there has been less direct comparison of their surface and bulk magnetic properties. Researchers from the UK, China and the USA used the X-ray magnetic circular dichroism (XMCD) technique at beamline I10 to investigate prototype magnetic TIs. XMCD is one of the most powerful tools for the study of surface phenomena, offering unique elemental selectivity and atomic-scale high sensitivity. The research team was able to quantitatively address the different magnetic moments and transition temperatures for the surface and the bulk of the TI. They demonstrated a ‘three-steps’ transition model, with a temperature window of around 15 K where the surface of the TI is magnetically ordered while the bulk is not.This research should lay the foundation for the development of thesematerials in the emerging information technologies. LiuW et al. doi: 10.1126/sciadv.aav208 Designing new superconductors Since the 1986 discovery of the high-temperature superconducting copper oxides (cuprates) researchers have been trying to engineer nickelate oxides (nickelates) to produce another high-temperature superconductor.With the recent discovery of the first nickelate superconductor, there has been a renewed focus in uncovering the electronic structures of the nickelate to further understand the mechanism of superconductivity and to prepare for the synthesis of other high- temperature superconductors. An international research team used the resonant inelastic X-ray scattering (RIXS) instrument at beamline I21 to uncover how the electrons of constituent ions hybridise to form the low energy electronic states from which superconductivity emerges. They discovered significant differences in the microscopic electronic structures of the nickelate compared with the cuprates that can now be used in the design and synthesis of new unconventional superconductors. Hepting M et al . doi: 10.1038/s41563-019-0585-z Improving energy efficiency Recent research at Diamond reveals new insights into the mechanisms underlying the piezoelectric properties of certainmaterials and how this could lead to the development of more energy-efficient electronic devices. The piezoelectric effect describes how some solids develop electric charge in response to an applied mechanical stress or vice versa. One example of how piezoelectric crystals convert electricity into mechanical energy is the automatic focusing of mobile phone cameras. An international team used beamline I06 to investigate the piezoelectric properties of a ceramic material called PMN-PT. By combining Photoemission Electron Microscopy (PEEM) with X-ray Magnetic Circular Dichroism (XMCD) while varying the voltage across the PMN-PT crystal, the team produced a magnetic vector map which initially showed the expected magnetic domains that seemingly rotated by 90° due to ferroelectric domain switching. However, high-resolution dataallowedapixel-by-pixelcomparisonoftheXMCD-PEEM imageswhichshowed that the magnetic switching angles typically fell well short of 90°. Although unexpected, this result could be explained by considering a shear component. This discovery should be applicable to other materials and will inform the development and miniaturisation of devices based on magnetoelectric materials. Ghidini M et al. doi: 10.1038/s41563-019-0374-8