Inauguration ceremony at beamline ID32

Inauguration ceremony at beamline ID32. Pictured from left to right: N. Brookes (Scientist in charge of ID32), Prof. D. McMorrow (SAC member), Prof. K. Hämäläinen (Chairman SAC),  F. Yakhou-Harris (ID32), Prof. M. Takata (SAC member), F. Sette (Director General).

One of the major events of the year 2014 was the start of operation of ID32, the upgrade beamline project UBPL7 dedicated to polarisation dependent studies using soft X-rays. This 120 m long beamline replacing the former ID08 features two branches, optimised for state-of-the-art X-ray magnetic circular dichroism (XMCD) experiments and resonant inelastic X-ray scattering (RIXS) with very high energy resolution. Among the upgraded features are a variable spot size down to 10x100 µm2 on the XMCD branch and a combined resolution of 30000 on the RIXS branch. ID32 was inaugurated on November 6 (see photo below). The first user group (Ghiringhelli et al., Politecnico di Milano, Italy) worked on the high field magnet (9 T) end station on the XMCD branch to investigate chiral effects in high temperature superconductors. The second group (Ogin et al., University of Exeter, UK) made use of the “free” experimental station, on the same branch, for time-resolved soft X-ray magnetic holography.

Another important result that marked the year 2014 was the success of the first high-power laser-shock experiment at the energy-dispersive X-ray absorption spectroscopy (XAS) beamline ID24, which was the upgrade beamline project UPBL11. For the first time at a synchrotron, iron was investigated while being dynamically compressed to extreme pressures and temperatures (~4 Mbar, 9000 K). A compact (30 J) focused laser beam was used to produce a hot compressed state in the sample, of sufficient duration to be probed with a single 100 ps X-ray pulse. The feasibility of a “single” shot scheme is very important because the reproducibility of such extreme conditions is never guaranteed. Usually, much larger, very high energy lasers are required to produce such extreme states making the experiments more costly and less accessible. The possibility of performing such experiments at a synchrotron beamline offers new opportunities to a large user community.

At beamline ID12, the high pressure programme reached a milestone early this year with the first ever measured chlorine K edge XAS at high pressure. The B1(NaCl-type) - B2(CsCl-type) structural phase transition (≈ 3 GPa) in a KCl crystal was recorded in total fluorescence yield mode through a specially-designed diamond-anvil cell featuring a fully-perforated diamond coupled to a thin 30 µm diamond window. The beam was focused in both directions by Be refractive lenses. This achievement opens exciting new opportunities for high pressure studies at low X-ray energies.

At beamline ID26, the KB mirror assembly was replaced. This, considerably improved the beam stability and increased the brilliance by a factor of 4. Following on from pioneering experiments where X-ray magnetic circular dichroism was combined with resonant inelastic X-ray scattering, a chamber was designed for permanent installation at the beamline holding phase plates to generate circular polarised light. Many samples measured at ID26 suffer radiation damage. This can be avoided by using a large amount of sample that is moved through the beam. To permit this, ID26 has developed hardware and software tools to map a large sample surface or liquid jets. Finally, ID26 is exploring the energy range from 2-5 keV in X-ray emission spectroscopy with a new instrument under design.

This year’s chapter reflects the large variety of different spectroscopic and scattering methods utilised at the ESRF to investigate the electronic and magnetic structure in materials that are becoming more and more diverse. In addition to the five beamlines of the Electronic Structure and Magnetism Group (ID12, ID24, ID26, ID32 and BM23), our chapter also hosts science highlights from ID20, the new Inelastic X-ray Scattering (IXS) beamline, and from BM28, the UK CRG beamline.

The science highlight from BM28 shows how the interference between non-resonant magnetic X-ray scattering and the pure quadrupole resonance at the Fe K absorption edge in the weak ferromagnet FeBO3 carries the sign of the Dzyaloshinskii–Moriya interaction. The selection from ID20 includes the investigation of high energy plasmonic excitations in transition metal dichalcogenides by IXS and the study of the electronic structure of the spin-orbit Mott insulator CaIrO3, where RIXS at the Ir L3 edge has been applied to explain its insulating behaviour.

RIXS in the soft X-ray regime has also been used for one of the last science highlights from beamline ID08 before its closure, to reveal differences between electronic excitations in electron- and hole-doped cuprates, a prerequisite for a complete understanding of the superconductivity in these systems. The second selection from ID08 shows an interesting application of soft XCMD to investigate the magnetic properties of surface-supported molecular systems employing transition metals dopants.

XMCD with hard X-rays, the work horse of the ID12 beamline, has also been used to unveil a novel dilute magnetic semiconductor, europium nitride, showing that it exhibits surprising properties that distinguish it from other materials in this class. A second highlight from ID12 concerns observation of strong magneto-chiral dichroism at the K-edges of transition metals in paramagnetic molecular helices. This peculiar type of dichroism is due to orbital toroidal currents which are of relevance for many phenomena, ranging from multiferroicity to superconductivity.

Valence-to-core XES is highly sensitive to small variations of a transition metal’s valence electronic structure induced by the ligand. In the first science highlight from beamline ID26, this technique has been used as a spectroscopic ruler for the quantitative determination of the NO oxidation state in Fe-NO complexes. Two additional highlights focus on the use of HERFD-XAS to probe the chemically active 4f orbitals of Ce in colloidal Ce oxide nanoparticles, and the oxidation state of Mo in the active site of the enzyme nitrogenase.

Remaining within the realm of catalysis, but moving from biology to inorganic chemistry, one of the science highlights from the pre-upgrade ID24 beamline reports on the spontaneous oscillatory behaviour in heterogeneous catalysts by means of the combination of time-resolved EXAFS with synchronous diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectroscopy.

To conclude, the two science highlights selected from the general purpose EXAFS beamline BM23 focus on the optimisation of Ru-doped spinels used as cathodes for high voltage lithium-ion batteries, and on revealing icosahedral bonding configurations in highly undercooled metals.

S. Pascarelli