The newly formed Magnetic Materials Group concentrates on emergent phenomena in quantum materials using the capabilities of beamlines I06, I10, I16, B16 and I21. The research encompasses avariety of challenges and opportunities at the frontiers of condensed matter physics and materials science ranging from topological states of matter, superconductivity, spintronics, two-dimensional systems, skyrmions and multiferroics. The key insights made by researchers exploit the high sensitivity of polarised X-ray spectroscopy, microscopy and scattering available across the beamlines. For instance, polarised soft X-rays combined with the PhotoEmission Electron Microscope (PEEM) on the Nanoscience beamline (I06) have visualised the domain dynamics underpinning antiferromagnetic spintronics while the resonant soft X-ray scattering on the BLADE: X-ray Dichroism and Scattering beamline (I10) has been used to understand the topological properties of skyrmions. On the Materials and Magnetism beamline (I16), interference effects in hard X-ray scattering have led to a deeper understanding of long-range magnetic ordering in canted antiferromagnets. The Inelastic X-ray Scattering beamline (I21) is in a commissioning phase, but has had already performed ground breaking experiments measuring orbital excitations, magnon dispersion and electron-phonon coupling in several highly-correlated systems. In this inaugural contribution to the annual highlights we present research from our user community that uniquely demonstrates how polarised X-ray science can uncover dramatic changes in the magnetic properties of materials from subtle changes to the geometric and electronic structure.
The origin of many complicated magnetic structures arises from short- range and long-range interactions. The understanding of long-range order arising from the Dzyaloshinskii-Moriya interaction (DMI) is, therefore, fundamental to developing new devices based on magnetoelectric effects. Building on previous work that determined the sign of the DMI for the weak ferromagnet, FeBO3, researchers on beamline I16 have gone a step further and unearthed the relationship between band filling and the sign of the DMI by studying a series of isostructural weak ferromagnetic carbonates. The change in sign of the DMI is correlated to the electronic structure using first-principles calculations and is a dramatic demonstration of how magnetic properties, that can be determined using polarised X-rays, are influenced by subtle changes to the electronic structure.
By depositing thin films of BiFeO3 on vicinal surfaces researchers on beamline I06 were able to grown single ferroelectric domain samples leading to deterministic and robust room-temperature control of the magnetic orientation of a Co overlayer. BiFeO3 is a multiferroic with a DMI that leads to a spin cycloid structure with a ~63 nm period. At first glance it might seem that such a complicated magnetic structure would have little effect on a Co overlayer. However, the combined use of Neutron Diffraction, at the nearby ISIS facility, and the PEEM on beamline I06 demonstrated that the interface region of the BiFeO3 structure has a collinear antiferromagnetic component that, upon reversal of the BiFeO3 electric polarisation using a bias voltage, is able to reproducibly switch the Co film magnetisation direction. These nanoscale insights into the interface region of single domain thin film BiFeO3 are only possible using the PEEM combined with polarised soft X-rays and show how controlling film structure can lead to new and robust functionality.
When inversion symmetry is broken using interface engineering in trilayers, the spin-orbit interaction leads to the spin-orbit torque (SOT) effect that can then be used to switch the magnetisation of a thin magnetic film. The size of the SOT depends sensitively on interface properties, but can also be tuned by altering the resistivity of the materials in the trilayer using ion sputtering during growth. On I10 researchers have employed this approach to relate the changes in the resistivity of a Pt layer, in a Pt/Co/AlOxtrilayer, to changes in the Co spin and orbital moments determined using X-ray Magnetic Circular Dichroism (XMCD).
In terms of technical developments across the beamlines we start with the latest addition to the suite of Diamond beamlines. I21 is a polarised soft X-ray beamline covering the energy range 250 eV to 3000 eV and dedicated to Resonant Inelastic X-ray Scattering. In the past few months the beamline team have started user operation and welcomed eight international research groups for first experiments. The novel collection geometry on I21 means that the beamline leads the world in detection efficiency and can perform scans in a fraction of the time that would otherwise be possible. The beamline has already achieved a resolution of 13.8±0.2 meV at the O K-edge (Fig. 1) and is now pressing ahead with further developments to reach higher photon energies covering the 4d and 5d transition metal 2p and 3p edges respectively, provide polarisation analysis of the scattered X-rays and install more efficient detectors. I10 is in the closing stages of installing a new electromagnet facility, to complement the existing low-temperature 14 T magnet, for fast XMCD measurements and is also installing a new versatile electromagnet in the RASOR diffractometer. I06 is completing the refurbishment of the branchline, which will permanently house the vector magnet and time-resolved soft X-ray diffraction systems. Beamline I06 has also started the process of installing a new Medipix3RX quad detector for the PEEM with a higher quantum efficiency with respect to the existing detector. In the coming year, I06 will also upgrade the PEEM manipulator to reach lower temperatures using liquid He enabling researchers to explore the phase diagrams of, for instance, multiferroics and superconductors. I16 have upgraded the polarisation analyser to house an area detector and is continuing to develop versatile polarisation control of the incoming X-rays. The main upgrade to the B16 Test beamline has been the design and development of a pink-beam compatible X-ray camera system, which overcomes the challenges from the high flux of white beam, including degradation of image quality due to accumulated contamination on the scintillator during intense X-ray exposure. This camera system will facilitate fast imaging on B16 using pink/white beams. Furthermore, in the B16 science highlight, a novel approach to selecting a single bunch using surface acoustic waves is presented.
The Magnetic Materials Group will continue developing the beamlines and off-line laboratories for the research community and would welcome input on how we can maintain the world-leading facilities developed at Diamond. In the long-term we are also working on the development of the facilities ready for an upgrade to the low-emittance Diamond-II machine. Our aim is to realise a family of polarised X-ray beamlines with intuitive software, underpinned by advanced on-site sample characterisation facilities and supported by state-of- the-art data visualisation tools.
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