R. Flacau

The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fm

Neutron diffraction and μSR studies of two polymorphs of nickel niobate NiNb2O6

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Frustrated magnetism in the double perovskite L a 2 LiOs O 6 : A comparison with L a 2 LiRu O 6

m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) A and 8.3435(4) A, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.

Structural phase transition in Ca H 2 at high pressures

In this report, we present a detailed powder x-ray diffraction study of the structural properties and charge density topology of structure I Xe clathrate hydrate under high pressure and room temperature. The pressure dependence of the structural parameters was determined by applying a Rietveld analysis to the experimental data. The combined Rietveld/maximum entropy method was used to derive the most probable charge density distribution at each pressure. Our results show that the charge density distribution of the encaged Xe atoms differs depending on the type of host cage at all pressures. Spherical electron density distributions were observed for the Xe atoms in the small cages while the atoms in the large cages showed longitudinal elongated electronic distributions. Along with the observed cage deformations, the change in electronic density distribution represents a clear indication that the guest-host interaction differs significantly between the small and large cages at high pressures. A similar behavior has been previously reported in low-temperature studies of methane clathrate hydrate.

Electron density topology of high-pressure Ba{sub 8}Si{sub 46} from a combined Rietveld and maximum-entropy analysis

Neutron diffraction and muon spin relaxation (

Pressure-Induced Changes on The Electronic Structure and Electron Topology in the Direct FCC → SH Transformation of Silicon

\mu

Structural Phase Transition in CaH2 at High Pressures

SR) studies are presented for the newly characterized polymorph of NiNb

Magnetic ground states in the three Os6+(5d2) double perovskites Ba2MOsO6(M=Mg,Zn,and Cd) from Néel order to its suppression

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