Pseudo-half-metalicity in the double perovskite Sr2_2CrReO6_6 from density-functional calculations

The electronic structure of the spintronic material Sr$_2$CrReO$_6$ is studied by means of full-potential linear muffin-tin orbital method. Scalar relativistic calculations predict Sr$_2$CrReO$_6$ to be half-metallic with a magnetic moment of 1 $\mu_B$. When spin-orbit coupling is included, the half-metallic gap closes into a pseudo-gap, and an unquenched rhenium orbital moment appears, resulting in a significant increase of the total magnetic moment to 1.28 $\mu_B$. This moment is significantly larger than the experimental moment of 0.9 $\mu_B$. A possible explanation of this discrepancy is that the anti-site disorder in Sr$_2$CrReO$_6$ is significantly larger than hitherto assumed.Comment: 3 Pages, 1 figure, 1 Tabl

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Phase Stability and Thermoelectric Properties of the Mineral FeS2: An Ab Initio Study

First principles calculations were carried out to study the phase stability and thermoelectric properties of the naturally occurring marcasite phase of FeS$_2$ at ambient condition as well as under pressure. Two distinct density functional approaches has been used to investigate the above mentioned properties. The plane wave pseudopotential approach was used to study the phase stability and structural, elastic, and vibrational properties. The full potential linear augment plane wave method has been used to study the electronic structure and thermoelectric properties. From the total energy calculations, it is clearly seen that marcasite FeS$_2$ is stable at ambient conditions, and it undergoes a first order phase transition to pyrite FeS$_2$ at around 3.7 GPa with a volume collapse of about 3$\%$. The calculated ground state properties such as lattice parameters, bond lengths and bulk modulus of marcasite FeS$_2$ agree quite well with the experiment. Apart from the above studies, phonon dispersion curves unambiguously indicate that marcasite phase is stable under ambient conditions. Further, we do not observe any phonon softening across the marcasite to pyrite transition and the possible reason driving the transition is also analyzed in the present study, which has not been attempted earlier. In addition, we have also calculated the electronic structure and thermoelectric properties of the both marcasite and pyrite FeS$_2$. We find a high thermopower for both the phases, especially with p-type doping, which enables us to predict that FeS$_2$ might find promising applications as good thermoelectric materials.Comment: 10 Figure

Use and Phytochemical Activity of Celosia Argentea Linn

Since ancient time in India. Celosia argentea linn. Is widely used in traditional medicine, to cure several disorders such as fever, diarrhea, mouth sores, itching wound, jaundice, gonorrhea and inflammation. Literaterature survey from books and journal of traditional Indian medicine revealed that celosia argentia linn. has a lot of medicinal properties. Leaves, stem and root have been reported for medicinal activity, the plant has pharmacologically been studied for various cativities like anti-cancer, hepatoprotection, anti-dibetes etc. However too many scientific studies have been carried out on this plant. For exploring these traditional uses. The present report is deals with traditional uses and pharmacological activity of celosia argentea linn. In the treatment of various diseases

Large chorangiomas: a seven years study in a tertiary care obstetrics and gynaecology hospital

Background: Chorangioma is a benign vascular placental tumour. It is composed of fetal capillary proliferation within the chorionic villi supported by a variable stroma. Smaller lesions are incidental, are often missed and carry no clinical significance. Larger lesions are associated with feto-maternal complications and are infrequently sent for histopathological examination.Methods: The study was conducted at the department of pathology, at a tertiary care obstetrics and gynaecology hospital. The study was a retrospective study which covered 7 years. Paraffin embedded blocks of placental specimens containing mass were taken up for the study. Sections were stained with haematoxylin and eosin (H and E). The results are compared and correlated with clinicopathologic factors. The statistical data are analysed manually.Results: A total of seven cases were included in the study, 4 cases were primi gravida, 1 case each in second, third and fourth gravida. Pregnancy outcome was intrauterine death in 1 case, dead born in 1 case, alive healthy children in 5 cases, birth weight was normal in 4 children, low birth weight in 2 children and 1 was extremely low birth weight. Of the total of 7 placental specimens 3 showed extraplacental mass and rest 4 showed intraplacental mass. All cases showed solitary lesions and measured > 5cm (large). Histopathological examination of all 7 specimens showed features of chorangioma.Conclusions: Careful inspection of the placenta is necessary following all deliveries. Any suspicious lesions should be documented and evaluated by histopathological examination there by predicting feto maternal complications and help the clinicians in better management of the mother and child accordingly. Meagre documentation of such cases prompted us to present this series of 7 cases of large chorangiomas with a mixed fetal outcome

Electronic topological transitions in Nb3X (X = Al, Ga, In, Ge, and Sn) under compression investigated by first principles calculations

First principles electronic structure calculations of A-15 type Nb3X (X = Al, Ga, In, Ge, and Sn) compounds are performed at ambient and high pressures. Mechanical stability is confirmed in all the compounds both at ambient as well as under compression from the calculated elastic constants. We have observed four holes and two electron Fermi surfaces (FS) for all the compounds studied and FS nesting feature is observed at M and along X-Γ in all the compounds. A continuous change in the FS topology is observed under pressure in all the compounds which is also reflected in the calculated elastic constants and density of states under pressure indicating the Electronic topological transitions (ETT). The ETT observed at around 21.5 GPa, 17.5 GPa in Nb3Al and Nb3Ga are in good agreement with the anomalies observed by the experiments

Thermoelectric properties of chalcopyrite type CuGaTe2 and chalcostibite CuSbS2

Electronic and transport properties of CuGaTe2, a hole-doped ternary copper based chalcopyrite type semiconductor, are studied using calculations within the Density Functional Theory and solving the Boltzmann transport equation within the constant relaxation time approximation. The electronic band structures are calculated by means of the full-potential linear augmented plane wave method, using the Tran-Blaha modified Becke-Johnson potential. The calculated band gap of 1.23 eV is in agreement with the experimental value of 1.2 eV. The carrier concentration- and temperature dependent thermoelectric properties of CuGaTe2 are derived, and a figure of merit of zT = 1.69 is obtained at 950 K for a hole concentration of 3.7 · 10 19 cm - 3, in agreement with a recent experimental finding of zT = 1.4, confirming that CuGaTe2 is a promising material for high temperature thermoelectric applications. The good thermoelectric performance of p-type CuGaTe2 is associated with anisotropic transport from a combination of heavy and light bands. Also for CuSbS2 (chalcostibite), a better performance is obtained for p-type than for n-type doping. The variation of the thermopower as a function of temperature and concentration suggests that CuSbS2 will be a good thermoelectric material at low temperatures, similarly to the isostructural CuBiS2 compound

Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites

We have investigated the magnetic moment of the W ion in the ferrimagnetic double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism (XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and positive orbital magnetic moment was detected. The experimental results are in good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the full-potential linear muffin-tin orbital method. It is remarkable, that the magnetic ordering temperature, TC, is correlated with the magnetic moment at the 'non-magnetic' W atom.Comment: accepted for publicatio