Diamond Annual Review 2021/22

48 49 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 1 / 2 2 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 1 / 2 2 MagneticMaterials Group Sarnjeet Dhesi, Science Group Leader T heMagnetic Materials Group (MMG) at Diamond Light Source 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). 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. In this contribution, we present research demonstrating how PEEM can map the antiferromagnetic textures in materials such as α-Fe 2 O 3 , which is under the spotlight for application in fast and energy-efficient computing. Learning how to control the formation of these textures could be the key to developing racetrack non-volatile memory for next-generation computing. Temperature-dependent REXS has uncovered a new magnetic order in ultra-thin SrRuO 3 films, which researchers believe corresponds to skyrmion lattice structure. This new quasi quantum particle could also soon be used for magnetic racetrackmemory. We also present results reporting the successful synthesis of a 2Dmagnet with great potential for use in low-dissipation electronics. Combining the power of XAS and X-ray Magnetic Circular Dichroism (XMCD) allowed unambiguous determination of the atomic- scale magnetic properties of the epitaxial CrTe 2 /graphene 2D magnets. Finally, RIXS is presently the only technique to measure magnetic excitations in momentum space from thin film samples only a few nanometers thick, a capability used here to investigate the structure of magnetic excitations in an infinite-layer nickelate (nickel oxide) superconductors. Revealing the microscopic electronic structures of the nickelate will inform the design and synthesis of new unconventional superconductors. Racetrack memory, a concept initially proposed by IBM, uses magnetic textures to store information bits (ones and zeros) rather than charge. It involves creating tiny textures (whirls) in a uniform magnetic medium and storing or retrieving them by moving them along a magnetic track. As textures persist when there is no power, racetrack memory could be highly stable and energy efficient. The original designs for racetrack memory used ferromagnets, but recent research has shown that the textures move much faster in antiferromagnets. However, antiferromagnetic textures are harder to manipulate and even, visualise. The Nanoscience beamline (I06) gives researchers complete control over the X-ray beam properties, and using PEEM has enabled mapping of antiferromagnetic textures in exquisite detail. This is the first step towards gaining full control over the formation of these textures and their future application in fast, energy-efficient memory devices. On the Materials and Magnetism beamline (I16), REXS has been used to search for direct evidence of magnetic skyrmions - swirls of magnetic moments - in ultra-thin SrRuO 3 . The results showed a new magnetic order believed to be a Topological Hall effect (THE), the fingerprint of magnetic skyrmions. The unique topological properties of magnetic skyrmions make them a promising candidate for racetrack memory applications. On I10, the Beamline for Advanced Dichroism Experiments (BLADE), XAS and X-ray Magnetic Circular Dichroism (XMCD) have been used to explore the synthesis of 2D magnets. As conventional electric and electronic devices waste energy as heat, new materials are needed to make them more energy efficient. 2D magnets are one promising option. However, producing them is challenging and understanding the synthesis process of 2D magnets and their microscopic properties is essential. The first successful synthesis of inch-scale epitaxial CrTe 2 /graphene 2D magnets offers tremendous potential for future devices. RIXS is presently the only technique that can extract magnetic excitations in the momentum space from thin film samples. On the RIXS beamline (I21), researchers used the high energy resolution and high photon flux to investigate the structure of magnetic excitations in NdNiO 2 , an infinite-layer nickelate (nickel oxide) superconductor. An important focus of superconductor research at the moment is to characterise the differences and similarities between nickelate superconductors and the cuprate superconductors. This study suggests that, like cuprates, nickelates are strongly correlated The goal of theMagnetic Materials Group is to operate state-of- the-art polarised X-ray beamlines with leading-edge data acquisition, data logging and data analysis software. electronic systems. This new information will help to design and produce new superconducting materials. In the past year there has been considerable activity augmenting and improving the facilities of the MMG. A recent upgrade to I21 gives access to a higher energy range (~3keV) allowing, for example, RIXS studies of the complex ferroelectric and magnetic properties of 4 d materials. The new 1.6T electromagnet facility on I10 is providing improved access to polarised spectroscopy measurements to explore trends in many samples of varying composition. On I16, the new polariser provides complete control of the X-ray polarisation down to~3.3keV to further understand chiral magnetic materials. I06 has undergone amajor upgradewith the installation of the newaberration- corrected PEEM and repurposing of the existing PEEM with a continuous-wave laser as the excitation source. The laser-based PEEM (funded by the EPSRC and developed with the Central Laser Facility) is to train the user community in using the many facilities of a PEEM, develop new sample environments and perform research through peer reviewed access. Looking to the years ahead, the MMG is developing a new beamline for Diamond-II for Coherent Soft X-ray Imaging and Diffraction. The CSXID beamline has been developed over the past two years with the help of a user working group with a final design planned for late 2022. The Magnetic Materials Group Laboratory also houses characterisation equipment allowing sample screening and inspection using SQUID magnetometry, Atomic Force Microscopy and X-Ray Diffraction and is set to expand its capabilities. Finally, the suite of MMG beamlines have migrated to a NeXus file structure allowing much richer sets of metadata to be captured which is an important first step toward automated data analysis, sample handling and data comparison between different sources. I21 beamline at Diamond Light Source