Spin-gap opening accompanied by a strong magnetoelastic response in the S=1 magnetic dimer system Ba3BiRu2O9

Neutron diffraction, magnetization, resistivity, and heat capacity measurements on the 6H-perovskite Ba3BiRu2O9 reveal simultaneous magnetic and structural dimerization driven by strong magnetoelastic coupling. An isostructural but strongly displacive first-order transition on cooling through T*=176 K is associated with a change in the nature of direct Ru-Ru bonds within Ru2O9 face-sharing octahedra. Above T*, Ba3BiRu2O9 is an S=1 magnetic dimer system with intradimer exchange interactions J0/kB=320 K and interdimer exchange interactions J'/kB=-160 K. Below T*, a spin-gapped state emerges with \Delta\approx220 K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long range-magnetic order.Comment: 5 pages, 5 figures, accepted by Physical Review

Crystal growth, Structure Determination and Magnetism of a New Hexagonal Rhodate: Ba9Rh8O24

Single crystals of Ba9Rh8O24, grown from a molten potassium carbonate flux, crystallize in the spacegroup R¯3c with lattice parameters of a = 10.0899(4) and c = 41.462(2) Å. Magnetic measurements on oriented single crystals reveal the existence of magnetic anisotrop

Identification de l'acétate de 3-mercaptohexanol, composé à forte odeur de buis, intervenant dans l'arôme des vins de Sauvignon

L'extraction sélective des thiols volatils présents dans un vin a l'état de traces, associée à l'analyse par couplage chromatographie en phase gazeuse (CPG)-détecteur à photométrie de flamme (DPF) et CPG-spectrométrie de masse (SM) de l'extrait obtenu, a permis d'identifier un nouveau constituant de l'arome des vins de Sauvignon, l'acétate de 3-mercaptohexanol, jusqu'ici seulement caractérise dans le fruit de la passion. Le seuil de perception dans l'eau et en solution modèle de ce composé fortement odorant évoquant le buis avec des nuances plus fruitées de pamplemousse et de fruit de la passion est de l'ordre de quelques ng/1. L'acétate de 3-mercaptohexanol pourrait contribuer significativement à l'arôme variétal des vins de Sauvignon.Identification of 3-mercaptohexyl acetate in Sauvignon wine, a powerful aromatic compound exhibiting box-tree odorSelective extraction of volatile mercaptans present in wines at trace levels, combined with capillary gas chromatographic (GC) analysis using flame photometric detector (FPD) revealed the presence of a previously unreported compound in Sauvignon wine. 3-mercaptohexylacetate was identified by comparison of chromatographic and mass spectrum data with those of the reference compound. This mercapto ester, recently found in passion-fruit, exhibits aroma reminiscent of box tree with grapefruit and passion fruit notes. Its perception threshold in water and model solution is around 2-4 ng/l. 3-mercaptohexylacetate may contribute to the typical varietal aroma of Sauvignon wines

Effects of copper fungicide spraying on volatile thiols of the varietal aroma of Sauvignon blanc, Cabernet Sauvignon and Merlot wines

In a three-year experiment, the effect of pre-veraison copper sprayings of vines on must composition and some volatile thiols contributing to the varietal aroma of Sauvignon blanc, Cabernet Sauvignon and Merlot wines was studied in comparison with folpet sprayings in the Bordeaux winegrowing region. The readivity of copper residues with thiols, mainly during the alcoholic fermentation, had a dramatic effect on the concentration of 4-mercapto-4-methylpentan-2-one and 3-mercaptohexanol in wines. However, copper sprayings, preferentially on the foliage, did not significantly increase copper residues in must; thiol concentrations in wines were very close to those found in wines obtained from vines sprayed with folpet. Therefore, this mode of spraying can be used to avoid the effects of copper treatment at veraison on the volatile thiols of the wines varietal aroma.

Structure Determination of Ba\u3csub\u3e8\u3c/sub\u3eCoRh\u3csub\u3e6\u3c/sub\u3eO\u3csub\u3e21\u3c/sub\u3e, a New Member of the 2H-Perovskite Related Oxides

Single crystals of Ba8CoRh6O21 were grown out of a potassium carbonate flux. The structure was solved by a general method using the superspace group approach. The superspace group employed was R3m(00γ)0s with a = 10.0431(1) Å, c1 = 2.5946(1) Å and c2 = 4.5405(1) Å, V = 226.60(1) Å3. Ba8CoRh6O21 represents the first example of an m = 5, n = 3 member of the A3n+3mA\u27nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides and contains chains consisting of six consecutive RhO6 octahedra followed by one distorted CoO6 trigonal prism. These chains in turn are separated from each other by [Ba]∞ chains

Magnetic anomalies in the spin chain system, Sr3_3Cu1−x_{1-x}Znx_xIrO6_6

We report the results of ac and dc magnetization (M) and heat-capacity (C) measurements on the solid solution, Sr$_3$Cu$_{1-x}$Zn$_x$IrO$_6$. While the Zn end member is known to form in a rhombohedral pseudo one-dimensional K$_4$CdCl$_6$ structure with an antiferromagnetic ordering temperature of (T$_N$ =) 19 K, the Cu end member has been reported to form in a monoclinically distorted form with a Curie temperature of (T$_C$ =) 19 K. The magnetism of the Zn compound is found to be robust to synthetic conditions and is broadly consistent with the behavior known in the literature. However, we find a lower magnetic ordering temperature (T$_o$) for our Cu compound (~ 13 K), thereby suggesting that T$_o$ is sensitive to synthetic conditions. The Cu sample appears to be in a spin-glass-like state at low temperatures, judged by a frequency dependence of ac magnetic susceptibility and a broadening of the C anomaly at the onset of magnetic ordering, in sharp contrast to earlier proposals. Small applications of magnetic field, however, drive this system to ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x = 0.75 or 0.25) significantly depress magnetic ordering; in other words, T$_o$ varies non-monotonically with x (T$_o$ ~ 6, 3 and 4 K for x = 0.25, 0.5, and 0.67 respectively). The plot of inverse susceptibility versus temperature is non-linear in the paramagnetic state as if correlations within (or among) the magnetic chains continuously vary with temperature. The results establishComment: 7 pages, 7 figures, Revte

Random interactions and spin-glass thermodynamic transition in the hole-doped Haldane system Y2−x_{2-x}Cax_xBaNiO5_5

Magnetization, DC and AC bulk susceptibility of the $S$=1 Haldane chain system doped with electronic holes, Y$_{2-x}$Ca$_x$BaNiO$_5$ (0$\leq$x$\leq$0.20), have been measured and analyzed. The most striking results are (i) a sub-Curie power law behavior of the linear susceptibility, $\chi (T)$$\sim$ $T$$^{-\alpha}$, for temperature lower than the Haldane gap of the undoped compound (x=0) (ii) the existence of a spin-glass thermodynamic transition at $T$$_g$ = 2-3 K. These findings are consistent with (i) random couplings within the chains between the spin degrees of freedom induced by hole doping, (ii) the existence of ferromagnetic bonds that induce magnetic frustration when interchain interactions come into play at low temperature.Comment: 4 pages, 4 figures, to appear in Phys. Rev.

Coexistence of Haldane gap excitations and long range antiferromagnetic order in mixed-spin nickelates R_2 Ba Ni O_5

The spin dynamics of the S=1 Ni-chains in mixed-spin antiferromagnets Pr_2 Ba Ni O_5 and Nd_x Y_2-x Ba Ni O_5 is described in terms of a simple Ginzburg-Landau Lagrangian coupled to the sublattice of rare-earth ions. Within this framework we obtain a theoretical explanation for the experimentally observed coexistence of Haldane gap excitations and long-range magnetic order, as well as for the increase of the Haldane gap energy below the Neel point. We also predict that the degeneracy of the Haldane triplet is lifted in the magnetically ordered phase. The theoretical results are consistent with the available experimental data.Comment: 4 pages, 1 figure, submitted to PRL An alternative derivation of main results and new references adde