Interplay of chemical pressure and hydrogen insertion effects in CeRhSn {\bf CeRhSn} from first principles

Investigations within the local spin density functional theory (LSDF) of the intermetallic hydride system ${\rm CeRhSnH_x}$ were carried out for discrete model compositions in the range $0.33 \leq x_H \leq 1.33$. The aim of this study is to assess the change of the cerium valence state in the neighborhood of the experimental hydride composition, ${\rm CeRhSnH_{0.8}}$. In agreement with experiment, the analyses of the electronic and magnetic structures and of the chemical bonding properties point to trivalent cerium for $1 \leq x_H \leq 1.33$. In contrast, for lower hydrogen amounts the hydride system stays in an intermediate-valent state for cerium, like in ${\rm CeRhSn}$. The influence of the insertion of hydrogen is addressed from both the volume expansion and chemical bonding effects. The latter are found to have the main influence on the change of Ce valence character. Spin polarized calculations point to a finite magnetic moment carried by the Ce $4f$ states; its magnitude increases with $x_H$ in the range $1 \leq x_H \leq 1.33$

First principles study of the electronic and magnetic structures of the tetragonal and orthorhombic phases of Ca3Mn2O7

On the basis of density functional theory electronic band structure calculations using the augmented spherical wave method, the electronic and magnetic properties of the orthorhombic and tetragonal phases of Ca3Mn2O7 were investigated and the spin exchange interactions of the orthorhombic phase were analyzed. Our calculations show that the magnetic insulating states are more stable than the non-magnetic metallic state for both polymorphs of Ca3Mn2O7, the orthorhombic phase is more stable than the tetragonal phase, and the ground state of the orthorhombic phase is antiferromagnetic. The total energies calculated for the three spin states of the orthorhombic phase of Ca3Mn2O7 led to estimates of the spin exchange interactions Jnn = -3.36 meV and Jnnn = -0.06 meV. The accuracy of these estimates were tested by calculating the Curie-Weiss temperature within the mean-field approximation.Comment: 11 pages, 7 figure

CEO Compensation And Firm Value

This paper examines the effect of CEO equity-based compensation (EBC) on firm value. In particular, we study the interaction between EBC and the percentage of independent directors as well as the interaction between EBC and managerial entrenchment. Our findings suggest a positive relation between firms’ value and EBC. Further, we show that the percentage of independent directors has a positive impact on the marginal effect of EBC on firm value

First principles investigations of the electronic, magnetic and chemical bonding properties of CeTSn (T=Rh,Ru)

The electronic structures of CeRhSn and CeRuSn are self-consistently calculated within density functional theory using the local spin density approximation for exchange and correlation. In agreement with experimental findings, the analyses of the electronic structures and of the chemical bonding properties point to the absence of magnetization within the mixed valent Rh based system while a finite magnetic moment is observed for trivalent cerium within the Ru-based stannide, which contains both trivalent and intermediate valent Ce.Comment: 6 pages, 7 figures, for more information see http://www.physik.uni-augsburg.de/~eyert

Nanoparticle corona artefacts derived from specimen preparation of particle suspensions

Progress in the implementation of nanoparticles for therapeutic applications will accelerate with an improved understanding of the interface between nanoparticle surfaces and the media they are dispersed in. We examine this interface by analytical scanning transmission electron microscopy and show that incorrect specimen preparation or analysis can induce an artefactual, nanoscale, calcium phosphate-rich, amorphous coating on nanoparticles dispersed in cell culture media. We report that this ionic coating can be induced on five different types of nanoparticles (Au, BaTiO3, ZnO, TiO2 and Fe2O3) when specimen preparation causes a significant rise in pH above physiological levels. Such a pH change reduces ionic solubility in the suspending media to permit precipitation of calcium phosphate. Finally, we demonstrate that there is no indication of a calcium-phosphorus-rich coating on BaTiO3 nanoparticles suspended in culture media when prepared without alteration of the pH of the suspending media and imaged by cryo-STEM. Therefore we recommend that future reports utilising nanoparticles dispersed in cell culture media monitor and report the pH of suspensions during sample preparation

119Sn solid state NMR and M\"ossbauer spectroscopic studies of the intermediate-valent stannide CeRuSn

The ternary stannide CeRuSn is a static mixed-valent cerium compound with an or-dering of trivalent and intermediate-valent cerium on two distinct crystallographic sites. 119Sn M\"ossbauer spectra showed two electronically almost identical tin atoms at 323 K, while at 298 K and below (77 and 4.2 K) two tin sites can clearly be distinguished. 119Sn solid state NMR experiments are performed to probe the local hyperfine fields at the two different Sn sites. 119Sn NMR powder spectra are nicely fitted with two Sn sites with nearly the same magnetic anisotropy, but with different absolute shift values. Both Sn sites are strongly affected by crossover-like transitions between 100 and 280 K. This local-site study confirms the superstructure modulations found in previous investiga-tions. Towards lower temperatures the powder spectra are broadened giving strong evidence for the antiferromagnetically ordered ground state