Valence Instability of YbCu2_2Si2_2 through its quantum critical point

We report Resonant inelastic x-ray scattering measurements (RIXS) in YbCu$_2$Si$_2$ at the Yb L$_{3}$ edge under high pressure (up to 22 GPa) and at low temperatures (down to 7 K) with emphasis on the vicinity of the transition to a magnetic ordered state. We find a continuous valence change towards the trivalent state with increasing pressure but with a pronounced change of slope close to the critical pressure. Even at 22 GPa the Yb$^{+3}$ state is not fully achieved. The pressure where this feature is observed decreases as the temperature is reduced to 9 GPa at 7K, a value close to the critical pressure (\itshape{p\normalfont{$_c$}}\normalfont $\approx$ 7.5 GPa) where magnetic order occurs. The decrease in the valence with decreasing temperature previously reported at ambient pressure is confirmed and is found to be enhanced at higher pressures. We also compare the f electron occupancy between YbCu$_2$Si$_2$ and its Ce-counterpart, CeCu$_2$Si$_2$

Les rayons X éclairent le magnétisme des multiferroïques

L’étude des solides multiferroïques, où l’ordre magnétique à longue portée coexiste avec l’ordre ferroélectrique, constitue un domaine dont l’expansion récente est liée à la découverte de matériaux présentant un fort couplage entre l’aimantation spontanée et la polarisation électrique. Notre travail, par diffraction élastique de rayons X polarisés, porte sur l’étude des effets de couplage entre spin et réseau dans certains matériaux multiferroïques qui développent un ordre magnétique complexe, responsable de la polarisation ferroélectrique macroscopique. On montre comment la diffraction magnétique non résonnante de rayons X offre une possibilité unique de trouver des réponses spécifiques concernant le type d’interactions microscopiques mises en oeuvre

Resonant and magnetic X-ray diffraction by polarized synchrotron radiation

The aim of these notes is to introduce the experimental methods and theoretical works in the domain of magnetic and resonant x-rays scattering on single crystals to investigate the electronic and magnetic long range order in strongly correlated electron systems. We highlight the role of the x-rays polarization analysis and control to determine the magnetic structure of materials and, more generally, the electronic long range order parameters responsible for the phase transitions

Tensorial interactions of X-rays

International audienceThe tensorial interactions of X-rays in crystals are reviewed here, including magnetic effects, both in X-ray absorption and X-ray scattering. After a brief historical description of the development of theoretical concepts and experimental work in the last two decades of the twentieth century and the first decade of the twenty-first century, their analysis is detailed. The basic theoretical formulae are provided with the main information about their origin and a necessary link to the original literature in order to analyze them in more depth. Two examples of the experimental detection of higher-order magnetoelectric multipoles are provided: in V2O3, using resonant elastic scattering techniques, and in GaFeO3, using X-ray absorption-based techniques

Iron Magnetism in Cubic Laves Phase Itinerant Ferromagnets.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Unusual Fe-Fe Interactions in the Itinerant Magnet UFe2.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe