Diamond Light Source - Annual Review 2022/23 - Concise Edition

24 25 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 2 / 2 3 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 2 / 2 3 MagneticMaterials Group T he Magnetic Materials Group develops and uses a range of polarised X-ray probes, including Resonant Inelastic X-ray Scattering (RIXS), Resonant Elastic X-ray scattering (REXS), X-ray Absorption Spectroscopy (XAS) and PhotoEmission Electron Microscopy (PEEM) on beamlines I06, I10, I16, and I21 to tackle a variety of challenges and opportunities in exploiting the changes in magnetic properties of on materials. Areas covered include topological states of matter, superconductivity, spintronics (the study of electron spinning and associatedmagnetism in solid state devices), two-dimensional systems, skyrmions (particles that may provide new forms of data storage) and multiferroics. Over the last year, our research community has used these probes to gain fundamental insights into new materials and how to tune materials to discover exotic new properties. Research from this group this year has included investigating ferroelectric superlattices, developing new methods of fast and energy efficient computing storage and discovering new superconductors that operate at closer to room temperature. REXS reveals chiral structures of polar vortices in ferroelectric superlattices Recent research discovered polar vortex domains consisting of polar dipole vectors in ferroelectric superlattices. Because of their high potential as next- generation memory devices or functional devices, it is important to understand in detail the structure of polar vortices because it affects their properties and how they can be utilised in devices. Resonant Elastic X-ray Scattering (REXS) offers a non-destructive method to understand the complete 3D structure of the vortex. An international team of researchers used Diamond’s I10 REXS to determine the distribution of the three-dimensional polar vectors formed in a PbTiO 3 /SrTiO 3 superlattice. The research team observed that the sign of X-ray Circular Dichroism varies depending on the incident angle of the X-rays. Using a newly developed quantitative calculation, they revealed that this resultmeant a three-dimensional vortex array structure, not a simple one-dimensional helix. This research on the polar structure of ferroelectrics corresponds to the counterpart of X-ray resonant magnetic scattering for the magnetic structure, which has already been extensively studied. These similarities naturally trigger X-ray resonant scattering studies on multiferroics that exhibit both properties at the same time. There is still no way to simultaneously measure two properties of the same atomor system, and X-ray resonant scattering is likely to be the answer. Kim, KT. et al. DOI: 10.1038/s41467-022-29359-5 Ferroelectric topological structures Although ferromagnetism and ferroelectricity are similar effects, they were thought to be fundamentally different. However, theoreticians suggested that we might see that the two phenomena are surprisingly similar if we could get a close enough look. In ferromagnetism, the Dzyaloshinskii–Moriya interaction (DMi) gives rise to effects such as skyrmions, which are potentially very useful for next-generation electronic devices (spintronics). If an analogous mechanism were present in ferroelectric materials, it would offer intriguing possibilities for future applications. A team of researchers used Diamond’s I16 beamline to perform high- resolution X-ray diffraction. The high resolution and high flux coupled with area detectors enabled them to study periodicities in reciprocal space with necessarily high resolution. The X-ray data showed periodicities in two orthogonal directions that are aligned with the orthorhombic crystal symmetries. The X-ray data are in complete agreement with the more myopic cross-sectional Transmission ElectronMicroscopy (TEM) and show that the observed topology indeed extends throughout the crystal. In the studied sample, the topologies arise from small tilts of the atomic positions within the crystal, which induce both a small electrical polarisation and strain. The observed ferroic topologies arise as the system attempts to minimise the internal energy. The observation of an electrical equivalent of the DMi shows that complex topologies of the polarisation are now possible. By changing the material properties, this interaction strength can be tweaked, driving new, ever more complex structures that can be stabilised. The plethora of technologies based on ferromagnetic spin textures shows what may be possible in these electrical equivalents. Rusu, D. et al. DOI 10.1038/s41586-021-04260-1 Charge-ordered phase in layered nickelates Unconventional high-temperature superconductors are at the core of quantum materials and advanced technological applications. Recently a new family of superconductorswith layerednickelate-oxide structurewas successfully obtained. The latest resonant X-ray spectroscopic studies reveal them to be very close cousins to copper-oxide superconductors (cuprates) An international team of researchers used Diamond’s I21-RIXS beamline. Resonant Inelastic X-ray Scattering (RIXS) is one of the few techniques capable of probing the charge-ordered state. In particular, owing to the sub-100 nm probing depth, RIXS is particularly suited for the nm-thick nickelate films. Moreover, as I21 is equippedwith high energy resolution and high photon flux, it is an ideal facility for this type of study. The research team found the charge-ordered states exist in the parent layered nickelate NdNiO2. They show strong resonance at both Ni 3d and Nd 5d states, illustrating the coupled electronic structure between the two. The charge-ordered state also shows clear temperature dependence, a hallmark of an ordered state with an electronic origin. Using the continuous tunability of the RIXS spectrometer, they found the charge-ordered state has non-negligible L-dependence, hinting it’s a three-dimensional object. Despite the differences to cuprates, the existence of the charge-ordered state demonstrates that the layered nickelates are remarkably similar to cuprate superconductors. Many materials in condensed matter physics exhibit remarkable properties such as zero-resistivity, colossal magneto-resistance and the magneto-optical Kerr effect. These novel properties lie in the competition of electronic and magnetic interactions under the angstrom and nanometre scale. A spectroscopy technique such as RIXS is imperative to understand and eventually make newer materials with richer functionality, due to its remarkable sensitivity. Tam, CC. et al. DOI: 10.1038/s41563-022-01330-1