Origin of ferromagnetism in Cs2_2AgF4_4: importance of Ag - F covalency

The magnetic nature of Cs$_{2}$AgF$_{4}$, an isoelectronic and isostructural analogue of La$_2$CuO$_4$, is analyzed using density functional calculations. The ground state is found to be ferromagnetic and nearly half metallic. We find strong hybridization of Ag-$d$ and F-$p$ states. Substantial moments reside on the F atoms, which is unusual for the halides and reflects the chemistry of the Ag(II) ions in this compound. This provides the mechanism for ferromagnetism, which we find to be itinerant in character, a result of a Stoner instability enhanced by Hund's coupling on the F

Frustration of tilts and A-site driven ferroelectricity in KNbO_3-LiNbO_3 alloys

Density functional calculations for K_{0.5}Li_{0.5}NbO_3 show strong A-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no stereochemically active A-site ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off-centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling.Comment: 4 pages, 5 figure

Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites

The prospects for high thermoelectric performance in phosphide skutterudites are investigated based on first principles calculations. We find that stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in that it is metallic. As such the band structure must be modified if high thermopowers are to be achieved. In analogy to the antimonides it is expected that this may be done by filling with La. Calculations for LaFe_4P_12 show that a gap can in fact be opened by La filling, but that the valence band is too light to yield reasonable p-type thermopowers at appropriate carrier densities; n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl

Influence of extrusion conditions on the colour of millet-legume extrudates using digital imagery

peer-reviewedColour acts as one of the triggers for acceptance of snack foods. Digital imaging in conjunction with Adobe Photoshop can help identification of variations in the colour of extruded products. Response surface methodology-based central composite rotatable designed experiments were conducted to understand the colour components and overall acceptability (OAA) of extruded snacks made from millet–legume blends, 12–28% legume, at different moisture content (MC) of 12–24% wet basis (w.b.), extruded at varying die head temperatures (DHT) from 160–200 °C, barrel temperatures from 100–140 °C and screw speeds of 100–140 rpm. A simple digital camera was used for capturing the images of the extrudates. An L*a*b* colour model (where L* is the black/ white element, a* is green/red and b* is blue/yellow) was used for colour characterisation and OAA was determined by a hedonic scale. It was inferred from the analysis of the resulting statistically valid second order models for the responses that all the colour components were significantly affected by the amount of legume in the extruder feed and by the DHT. It was also observed that DHT, synergistically with other processing parameters, had a significant effect on all the responses. The OAA was highest for the extrudates with higher L* values. Optimum processing conditions were derived while the responses adhered to constraints. The responses of the extrudates prepared under optimum conditions exhibited no significant variation from model predicted values

Antisite Domains in Double Perovskite Ferromagnets: Impact on Magnetotransport and Half-metallicity

Several double perovskite materials of the form A_2BB'O_6 exhibit high ferromagnetic T_c, and significant low field magnetoresistance. They are also a candidate source of spin polarized electrons. The potential usefulness of these materials is, however, frustrated by mislocation of the B and B' ions, which do not organise themselves in the ideal alternating structure. The result is a strong dependence of physical properties on preparative conditions, reducing the magnetization and destroying the half-metallicity. We provide the first results on the impact of spatially correlated antisite disorder, as observed experimentally, on the ferromagnetic double perovskites. The antisite domains suppress magnetism and half-metallicity, as expected, but lead to a dramatic enhancement of the low field magnetoresistance.Comment: 6 pages, pdflatex, EPL styl