Emergence of a hidden magnetic phase in LaFe11.8Si1.2 investigated by inelastic neutron scattering as a function of magnetic field and temperature

The NaZn13 type itinerant magnet LaFe13−xSix has seen considerable interest due to its unique combination of large magnetocaloric effect and low hysteresis. Here, this alloy with a combination of magnetometry, bespoke microcalorimetry, and inelastic neutron scattering is investigated. Inelastic neutron scattering reveals the presence of broad quasielastic scattering that persists across the magnetic transition, which is attributed to spin fluctuations. In addition, a quasielastic peak is observed at Q = 0.52 Å−1 for x = 1.2 that exists only in the paramagnetic state in proximity to the itinerant metamagnetic transition and argue that this indicates emergence of a hidden mag the netic phase that drives the first-order phase transition in this system

Soft striped magnetic fluctuations competing with superconductivity in Fe1+xTe

Neutron spectroscopy is used to investigate the magnetic fluctuations in Fe1+xTe - a parent compound of chalcogenide superconductors. Incommensurate "stripelike" excitations soften with increased interstitial iron concentration. The energy crossover from incommensurate to stripy fluctuations defines an apparent hourglass dispersion. Application of sum rules of neutron scattering find that the integrated intensity is inconsistent with an S=1Fe2+ ground state and significantly less than S=2 predicted from weak crystal field arguments pointing towards the Fe2+ being in a superposition of orbital states. The results suggest that a highly anisotropic order competes with superconductivity in chalcogenide systems. © 2014 American Physical Society

Crystal and magnetic structure of cesium superoxide

CsO2 is a member of the family of alkali superoxides formula AO2 with A Na, K, Rb, and Cs that exhibit magnetic behavior arising from open p shell electrons residing on O amp; 8722;2 molecules. We use neutron diffraction to solve the crystal and magnetic structures of CsO2 and observe a complex series of structures on cooling from room temperature to 1.6 K. These include an incommensurate modulation along the a axis of the structure at intermediate temperatures, which then locks into a commensurate modulation that doubles the unit cell compared to the previously supposed orthorhombic unit cell. In both incommensurate and commensurate phases, our structural solution involves a staggering of the cesium ion positions along the b axis, in contrast to studies of other alkali superoxides in which staggered tilts of the O amp; 8722;2 dimers relative to the c axis are seen. Below T 10 K, we observe magnetic Bragg reflections arising from an antiferromagnetically ordered structure with a wave vector of k 0, 0, 0 relative to the doubled crystallographic unit cell , with moments that point predominantly along the b axis with a small component along the a axis that hints at possible anisotropic exchange coupling consistent with the crystal structure . Measurements of the magnetic Bragg reflections in an applied magnetic field suggest a spin flop transition takes place between 2 T and 4 T in which moments likely flop to point along the crystallographic a axis. Our measurements indicate that CsO2 is an interesting example of magnetic properties being inherently linked to the crystal structure, in that the staggered displacement of the cesium ions activates antisymmetric exchange, which then permits the observed spin cantin

REXS contribution to electronic ordering investigation in solids

Resonant Elastic X-Ray Scattering (REXS) has played a fundamental role in understanding electronic properties and in revealing hidden order, local symmetries and exotic states realized in correlated solids. This article reports on some of the relevant scientific contributions and technical advances over the last 20 years, by providing a list of related publications produced by various groups all around the world. The given perspective is that of a group of young scientists involved at various times in the investigation of the beauty of electronic ordering by the REXS technique. © 2012 EDP Sciences, Springer-Verlag