The current status and technical details of the four instruments dedicated to X-ray spectroscopy available at Diamond Light Source are presented.

Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases.

Understanding the fundamental spin coupling mechanisms in dilute magnetic oxides is not possible without exact atomistic understanding of the solids. This is even more important for few systems that show dilute ferromagnetism at room temperature and could potentially be used in spintronic and multiferroic technologies. Here, we show the first known example of a cation ordering in hexagonal 6H-perovskites. Fe 3+ ions in Fe-doped 6H-BaTiO 3 are initially randomly distributed over two Ti 4+ crystallographic sites but can be, by a prolonged heat treatment, ordered onto one of the sites. The cation ordering is driven by reduction in the electrostatic repulsion, which occurs when Fe 3+ substitutes the highly charged Ti 4+ ions that are located at unusual proximity to each other. We show that such a continuous order−disorder transition is associated with induction of the room-temperature dilute ferromagnetism.

Understanding an interaction at an interface between a topological insulator and a metal is of critical importance when designing electronic and spintronic devices or when such systems are used in catalysis. In this paper, we report on a chemical instability of the interface between Bi 2 Se 3 and Ag studied by X-ray powder diffraction and electron microscopy. We present strong experimental evidence of a redox solid-state reaction occurring at the interface with kinetics that is significant already at room temperature. The reaction yields Ag 2 Se, AgBiSe 2 , and Bi. The unexpected room-temperature chemical instability of the interface should be considered for all future theoretical and applicative studies involving the interface between Bi 2 Se 3 and Ag.

Highlights Au evaporated on Bi2Se3 at RT forms islands according to the Volmer-Weber growth mode  upon annealing to 100° C the Au deposits are not stable and assemble into larger and thicker islands  the Topological surface state (TSS) of Bi2Se3 is weakly affected by the presence of Au  at the Au/Bi2Se3 interface there is a weak chemical instability that results in Bi diffusion toward the surface of Au islands and in a chemical interaction between Au and atomic Se limited at the interfacial region  for the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10 -8 mbar) regime AbstractWe report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3 (0001) single crystal surface. At room temperature Au forms islands, according to the Volmer-Weber growth mode. Upon annealing to 100° C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, suchas Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10 -8 mbar) regime.