Effect of Spin Dilution on the Magnetic State of Delafossite CuFeO2 with an S = 5/2 Antiferromagnetic Triangular Sublattice

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Evidence for Unnatural-Parity Contributions to Electron-Impact Ionization of Laser-Aligned Atoms

Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this work we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. We demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionization from excited Ca and Na atoms

Effects of conservation and standard tillage on soil physico-chemical properties and overall quality in a semi-arid agrosystem

Shifting agricultural operations to more sustainable management practices is needed in the face of a changing climate. In this study, the short-term effects of three tillage systems (no-tillage, minimum tillage, and conventional tillage) on a wide selection of soil properties in a semi-arid agrosystem of eastern Tunisia were assessed. The studied soil properties included saturation percentage, bulk density, penetration resistance, mean weight diameter, electric conductivity, soil reaction, soil organic matter, carbonates, available phosphorus and exchangeable potassium. The impacts of tillage systems on soil quality indices (SQI) developed based on the total set of properties (SQI-T), or a minimum set (SQI-M) selected through principal component analysis, were also investigated. Relative to conventional tillage, no tillage increased bulk density, penetration resistance and electrical conductivity, whereas minimum tillage affected only saturation percentage and pH. No-till and minimum tillage did not enhance soil quality relative to conventional tillage. The SQI-T and SQI-M were highly correlated (r=0.93) to each other suggesting that the outcomes of the two indices are comparable. Principal component analysis efficiently selected the most influential indicators of the effects of tillage systems on soil quality. Farmers in the study region are encouraged to consider minimum tillage during the early years of transition from standard to no-tillage systems to avoid rapid decline in soil quality and consequent yield loss

Evidence for unnatural-parity contributions to electron-impact ionization of laser-aligned atoms

Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this work we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. We demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionization from excited Ca and Na atoms

Caractérisation et étude structurale de NaHo(PO3_3)4_4

Crystals of NaHo(PO$_3$)$_4$ have been grown by the flux technique and characterized by X-ray diffraction and infrared spectroscopy. Single crystal structure of NaHo(PO$_3$)$_4$ has been solved, it crystallizes in the monoclinic P2$_3$/n space group with lattice parameters : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. The crystal structure has been refined yielding a final R(F$^{2}$) = 0.033 for 2064 independent reflections (F$_o$$^{2}$ $\geq$ 2$\sigma$(F$_o$$^{2}$)). The NaHo(PO$_3$)$_4$ structure is characterized by helical ribbons (PO$_3$)$_\infty$ running along the c-axis. The HoO8 and NaO7 polyhedra form zigzag chains with common faces and surrounded by four (PO$_3$)$_\infty$ chainsLe polyphosphate NaHo(PO$_3$)$_4$ est synthétisé, sous forme de monocristaux, par la méthode de flux; ce composé est caractérisé par diffraction RX et spectroscopie de vibration IR. L’étude structurale de NaHo(PO$_3$)$_4$ a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d’espace P21/n, les paramètres de maille sont : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. L’affinement conduit à un facteur de confiance R1= 3,3 % pour 2064 réflexions indépendantes. La structure de NaHo(PO$_3$)$_4$ est caractérisée par une chaîne hélicoïdale (PO$_3$)$_\infty$ se développant le long de l’axe c. Les polyèdres HoO$_8$ et NaO$_7$ forment des chaînes en zigzag possédant des faces en commun et entourés par quatre chaînes (PO$_3$)$_\infty$

Caractérisation spectroscopique et étude structurale de RbEr(PO3_3)4_4

Crystals of RbEr(PO$_3$)$_4$ have been grown by the flux technique and characterized by X-ray diffraction, UV-Vis absorbance and infrared spectroscopy. Single crystal structure of RbEr(PO$_3$)$_4$ has been solved, it crystallizes in the monoclinic P21/n space group with lattice parameters : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. The crystal structure has been refined yielding a final R(F$_2$) = 0.026 for 2206 independent reflections (F$_o$$^{2}$ $\geq$ 2$\sigma$(F$_o$$^{2}$)). The RbEr(PO3)4 structure is characterized by helical ribbons (PO$_3$)$_\infty$ running along the c-axis. The erbium ions have an eightfold coordination. The ErO$_8$ polyhedra are isolated from each other in the sense that they do not share any oxygen atom. The minimal distance between two atoms of erbium is 6,2583 Å.Le polyphosphate RbEr(PO$_3$)$_4$ est synthétisé, sous forme monocristalline, par la méthode de flux ; ce composé est caractérisé par diffraction RX, spectroscopie d’absorption optique et spectroscopie de vibration IR. L’étude structurale de RbEr(PO$_3$)$_4$ a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d’espace P21/n, les paramètres de maille sont : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. L’affinement conduit à un facteur de confiance R(F2) = 0.026, pour 2206 réflexions indépendantes (Fo2 $\geq$ 2$\sigma$(Fo2)). La structure de RbEr(PO$_3$)$_4$ est caractérisée par une chaîne hélicoïdale (PO$_3$)$_\infty$ se développant le long de l’axe c. Les atomes d’erbium ont un environnement de 8 oxygènes. Les polyèdres ErO$_8$ sont isolés les uns des autres, ils ne présentent aucun atome d’oxygène en commun. La distance Er-Er la plus courte mesure 6,258 (Å)

Lower and Middle Jurassic ammonoids of the Shemshak Group in Alborz, Iran and their palaeobiogeographical and biostratigraphical importance

The Shemshak Group at Shahmirzad (northern Iran) is characterized by the most frequent and extensive marine intercalations and contains the most abundant and diverse ammonite faunas hitherto known from the Lower and lower Middle Jurassic strata of the Alborz Range. So far, 62 ammonite taxa have been recorded from this area, including 25 taxa from earlier studies. The taxa belong to the families Cymbitidae, Echioceratidae, Amaltheidae, Dactylioceratidae, Hildoceratidae, Graphoceratidae, Hammatoceratidae, Erycitidae, and Stephanoceratidae with the new species Paradumortieria elmii and Pleydellia (P.?) ruttneri. The fauna represents the Late Sinemurian, Late Pliensbachian, Toarcian, Aalenian, and Early Bajocian. Palaeobiogeographically, it is closely related to the Northwest European (Subboreal) Province, and exhibits only minor relations with the Mediterranean (Tethyan) Province

Cationic doping effect on the structural, magnetic and spectroscopic properties of delafossite oxides CuCr1−x(Sc,Mg)xO2

International audienceThis article reports the effect of Sc and (Sc + Mg) substitution on the structural and physical properties of delafossite-type CuCrO2 oxide. X-ray diffraction and Raman spectroscopy show that the structure is maintained for 10% Sc and (10% Sc + 4% Mg) substitutions for chromium. The incorporation of these elements generates very anisotropic microstrains in the structure. Strain also increases with oxygen intercalation, probably because a non-uniform distribution of intercaled oxygen. Thermal stability in oxygen was found to decrease with increasing the M3+ cation size. The evolution of relative intensities of Raman bands points towards an increase in lattice distortion with substitution, in agreement with ionic radii considerations. Comparing the substitution effect of Mg2+ to those of the nonmagnetic Sc3+, magnetization around the AF transition does not seem to correlate with randomness and lattice parameter but with itinerancy of the doped hole