P.P. Deen

Pressure device for resonant magnetic x-ray scattering

A pressure device has been developed and adapted to resonant x-ray magnetic scattering (RXMS) technique. The system is optimized for diffraction studies and allows a wide angular aperture in the scattering plane. Pressure changes are made in situ with pressure determination by the ruby fluorescence method. Since the whole device is compatible with a standard Orange cryostat, an extended (p,T) phase space, with T=1.4–300K and p=0–30kbar, can now be probed by RXMS. As an illustration, first results on Ce(CoxFe1−x)2 single crystal are presented. Such a pressure device can be equally used for other than RXMS techniques as shown with the study at low temperature of SmS under pressure using x-ray fluorescence measurements.

A Low Temperature Two‐Axis Goniometer for Azimuth Dependent Studies

A novel insert was developed for top‐loading liquid helium cryostats that allows a combined ±90°sample tilt with a full 360° azimuthal rotation. This sample stick is operational down to 1.5 K and was primarily designed for X‐ray scattering in reflecting geometry. The device not being intended for scanning but positioning purposes, motion precision, resolution and repeatability specifications were relaxed to 0.1°and readily achieved. This setup was initially designed for a specific cryostat and implemented at beamline ID20 of the ESRF but it can be easily adapted to similar top loading cryostats including cryomagnets. Initial results on the low temperature phases of CeB6 are presented.

Electronic and magnetic order in La0.7Ca0.3MnO3/YBa2Cu3O7-δLa0.7Ca0.3MnO3/YBa2Cu3O7-δ superlattices

Resonant X-ray scattering experiments have been performed on a heterostructure comprising ferromagnetic (La0.7Ca0.3MnO3)100A and superconducting (YBa2Cu3O7-δ)100A blocks. These measurements have probed a superstructure with wavevector q=(0.50.50), originating from the distortion of the MnO6MnO6 octahedra responsible for the ferromagnetic state in the La0.7Ca0.3MnO3La0.7Ca0.3MnO3 blocks. An intriguing temperature dependence of the integrated intensities indicates the rotation of the distorted MnO6MnO6 octahedra with the onset of both ferromagnetic and superconducting order, correlated via SQUID magnetisation and resistivity measurements.

Electronic and magnetic order in La0.7Ca0.3MnO3 /YBa2Cu3O7- δ superlattices

Resonant X-ray scattering experiments have been performed on a heterostructure comprising ferromagnetic (La0.7Ca0.3MnO3)100A and superconducting (YBa2Cu3O7-δ)100A blocks. These measurements have probed a superstructure with wavevector q=(0.50.50), originating from the distortion of the MnO6MnO6 octahedra responsible for the ferromagnetic state in the La0.7Ca0.3MnO3La0.7Ca0.3MnO3 blocks. An intriguing temperature dependence of the integrated intensities indicates the rotation of the distorted MnO6MnO6 octahedra with the onset of both ferromagnetic and superconducting order, correlated via SQUID magnetisation and resistivity measurements.

Electronic and magnetic order in superlattices

Resonant X-ray scattering experiments have been performed on a heterostructure comprising ferromagnetic (La0.7Ca0.3MnO3)100A and superconducting (YBa2Cu3O7-δ)100A blocks. These measurements have probed a superstructure with wavevector q=(0.50.50), originating from the distortion of the MnO6MnO6 octahedra responsible for the ferromagnetic state in the La0.7Ca0.3MnO3La0.7Ca0.3MnO3 blocks. An intriguing temperature dependence of the integrated intensities indicates the rotation of the distorted MnO6MnO6 octahedra with the onset of both ferromagnetic and superconducting order, correlated via SQUID magnetisation and resistivity measurements.

Probing the (p,T ) phase diagram of CeFe2 and SmS using resonant x-ray scattering

Two strongly correlated electron systems CeFe2 and SmS have been studied using x-ray magnetic resonant scattering at low temperatures and high pressures. First, the magnetic ground state of CeFe2 doped with 7% Co has been probed by means of resonant x-ray magnetic scattering across the temperature range 10–95 K at pressures up to 9.5 kbar. A strong increase of the Neel temperature with pressure has been evidenced. Furthermore, a large increase in scattering intensity is observed just before TN at 9.5 kbar. These results reveal that the itinerant character of the 4f electrons which stabilize the antiferromagnetic state has been probed. Secondly, the structural and electronic properties of SmS have been studied under pressure up to 29 kbar and at temperatures down to 4.5 K via absorption and diffraction techniques. The measurements are a direct probe of the valence of Sm in SmS at low temperature from the black insulator phase to the gold metallic phase and furthermore across the magnetic transition. In particular, it is found that Sm in SmS has an intermediate valence (2.81(4)) in the magnetically ordered phase at 29 kbar and 4.5 K.