Interplay of Chemical Bonding and Magnetism in Fe_4N, Fe_3N, Fe_2N

Using spin density functional theory we have carried out a comparative study of chemical bonding and magnetism in Fe_4N, Fe_3N and Fe_2N. All of these compounds form close packed Fe lattices, while N occupies octahedral interstitial positions. High spin fcc Fe and hypothetical FeN with rock salt structure have been included in our study as reference systems. We find strong, covalent Fe-N bonds as a result of a substantial \sigma-type p-d hybridisation, with some charge transfer to N. Those Fe d orbitals which contribute to the p-d bonds, do no longer participate in the exchange splitting of the Fe d bands. Because of the large exchange fields, the majority spin d bands are always fully occupied, while the minority spin d bands are close to half-filling, thus optimizing the Fe d-d covalent bonding. As a consequence, in good approximation the individual Fe moments decrease in steps of 0.5 \mu_B from fcc iron (2.7 \mu_B) via Fe_4N (2.7 and 1.97 mu_B}), \chem{Fe_3N} (1.99 \mu_B) to \zeta - Fe_2N (1.43 \mu_B).Comment: 16 pages, 15 figure

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 $1 \leq x_H \leq 1.33$

Electronic and Magnetic Properties of Fe 2

The electronic and magnetic properties of the nitrides Fe2N and hypothetical FeN were investigated by use of the ASW method. For both nitrides, the calculations were done in the orthorhombic structure of Fe2N for the two nitrides. The magnetization is low (0.95 μB/at.) for Fe2N and vanishes for FeN. The decrease of the magnetization with increasing amount of N is assessed within the Fe-N system in a model derived from a Slater-Pauling type behavior. Accordingly, a trend from weak to strong ferromagnetism is suggested

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

Integration of the ASTER thermal infra-red bands imageries with geological map of Jabal Al Hasir area, Asir Terrane, the Arabian Shield

AbstractThermal infra-red bands of Advanced Spaceborne Thermal Emission and Radiometer (ASTER) have been used to investigate rocks, including white quartz veins, of Jabal Al Hasir area of the Asir Terrane, southwestern part of the Arabian Shield. The obtained data were processed using radiometric and geometric corrections. The processed data were then enhanced into false color images by Thermal Infra Red band ratioing. These composite images clearly differentiate between the light color felsic granite rocks and the dark color mafic gabbroic rocks. These images also differentiate quartz veins from wadi deposits, although, both of them appear very similar in light color and light grayscale tone. Results of the band ratioing have also been compared with the geological map of the study area, and were found in agreement. Keeping in view the obtained resolution, the band ratioing images have been found more informative and useful than the regular color composite images. Based on these observations, it can be claimed that the ASTER sensor is more powerful in terms of geological applications. Due to its success in the study area, the use of this sensor could also be extended to other complicated areas in the Arabian Shield and beyond

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