Publications | Understanding “forbidden” reflections

Understanding “forbidden” reflections

A team from Diamond and their colleagues from Russia, France and Germany have taken advantage of the versatility of the Materials and Magnetism beamline (I16) to gain a detailed understanding of the fundamental interaction mechanisms between crystals and X-rays.

Fe3BO6

The group used a crystal of iron orthoborate (Fe3BO6) to study a technique called Resonant X-Ray scattering (RXS), both at Diamond and on the European Synchrotron Radiation Facility (ESRF) XMaS beamline in Grenoble.

RXS, which has been developed for the last two decades, is a promising technique due to its sensitivity to local properties of crystals such as magnetic order or thermal vibrations. It allows the observation of forbidden reflections that can only be seen with synchrotron radiation. These forbidden reflections carry some unique information on the electronic environment of a particular atom in the crystal. But this information is encoded in the complex scattering processes of RXS and most studies are performed on samples with simple crystal structures.

The group chose Fe3BO6 for its structure properties, in particular its level of symmetry and the existence of two inequivalent crystallographic positions for the Fe cation. Because of these properties, Fe3BO6 proved to be a much more complicated case to study by RXS than the crystals used previously. The scientists studied theoretically and experimentally the forbidden reflections measured by RXS in order to analyse and disentangle the various contributions and effects explaining their energy spectra. In particular, measurements at room temperature were carried out at the ESRF while complementary measurements at ambient, as well as low and high temperatures, were done on I16 using the same sample: a platelet with faces a few square millimetres in size and a thickness of a few hundred microns.

Although the measurements were affected by poor crystal quality and other technical difficulties, the group managed to extract excellent experimental data. It also demonstrated the remarkable sensitivity of RXS to the interplay of various scattering contributions.

Scientists at Diamond plan to carry on their RXS studies taking advantage of the I16 versatility.

Interplay of inequivalent atomic positions in resonant X-ray diffraction of Fe₃BO₆, G Beutier, E Ovchinnikova, S P Collins, V E Dmitrienko, J E Lorenzo, J-LHodeau, A Kirfel, Y Joly, A A Antonenko, V A Sarkisyan and A Bombardi J. Phys.: Condens. Matter 21 (2009) 265402
DOI: 10.1088/0953-8984/21/26/265402

<< Probing average size of metal nanoparticles | I13 begins to take shape outside the doughnut >>