452 research outputs found
Interplay of chemical pressure and hydrogen insertion effects in from first principles
Investigations within the local spin density functional theory (LSDF) of the
intermetallic hydride system were carried out for discrete
model compositions in the range . The aim of this
study is to assess the change of the cerium valence state in the neighborhood
of the experimental hydride composition, . In agreement
with experiment, the analyses of the electronic and magnetic structures and of
the chemical bonding properties point to trivalent cerium for . In contrast, for lower hydrogen amounts the hydride system stays in an
intermediate-valent state for cerium, like in . 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 states; its magnitude increases
with in the range
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
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