Comparative investigation of the coupled-tetrahedra quantum spin systems Cu2Te2O5X2, X=Cl, Br and Cu4Te5O12Cl4

We present a comparative study of the coupled-tetrahedra quantum spin systems Cu2Te2O5X2, X=Cl, Br (Cu-2252(X)) and the newly synthesized Cu4Te5O12Cl4 (Cu-45124(Cl)) based on ab initio Density Functional Theory calculations. The magnetic behavior of Cu-45124(Cl) with a phase transition to an ordered state at a lower critical temperature T$_c$=13.6K than in Cu-2252(Cl) (T$_c$=18K) can be well understood in terms of the modified interaction paths. We identify the relevant structural changes between the two systems and discuss the hypothetical behavior of the not yet synthesized Cu-45124(Br) with an ab initio relaxed structure using Car-Parrinello Molecular Dynamics.Comment: 2 pages, 1 figure; submitted to Proceedings of M2S-HTSC VIII, Dresden 200

Effect of isoelectronic doping on honeycomb lattice iridate A_2IrO_3

We have investigated experimentally and theoretically the series (Na$_{1-x}$Li$_{x}$)$_{2}$IrO$_{3}$. Contrary to what has been believed so far, only for $x\leq0.25$ the system forms uniform solid solutions. For larger Li content, as evidenced by powder X-ray diffraction, scanning electron microscopy and density functional theory calculations, the system shows a miscibility gap and a phase separation into an ordered Na$_{3}$LiIr$_2$O$_{6}$ phase with alternating Na$_3$ and LiIr$_2$O$_6$ planes, and a Li-rich phase close to pure Li$_{2}$IrO$_{3}$. For $x\leq 0.25$ we observe (1) an increase of $c/a$ with Li doping up to $x=0.25$, despite the fact that $c/a$ in pure Li$_{2}$IrO$_{3}$ is smaller than in Na$_{2}$IrO$_{3}$, and (2) a gradual reduction of the antiferromagnetic ordering temperature $T_{N}$ and ordered moment. The previously proposed magnetic quantum phase transition at $x\approx 0.7$ may occur in a multiphase region and its nature needs to be re-evaluated.Comment: 8 pages, 9 figures including supplemental informatio

Notas corológicas del macrofitobentos de Andalucía (España). VII

El presente trabajo añade nuevas especies a los catálogos de algas Rhodophyceae (Conde et al., 1996b), Phaeophyceae (Flores- Moya et al., 1995a) y Chlorophyceae (Flores-Moya et al., 1995b) existentes para las costas andaluzas, aumentando de este modo el conocimiento florístico del macrofitobentos de Andalucía. La mayoría de las aportaciones proceden de cubetas intermareales de la Isla de las Palomas (Tarifa, Cádiz), excepto una de Punta Carnero (Cádiz) y una de Marina del Este (Granada). En conjunto se aportan una cita nueva para Andalucía (señalada con un asterisco), cinco citas nuevas y tres confirmaciones para la provincia de Cádiz, y una novedad para el catálogo de la provincia de Granada.El material recolectado fue preservado en formol al 4% en agua de mar, identificado y depositado en el herbario de la Universidad de Málaga (MGC Phyc)

The monoclinic crystal structure of α\alpha-RuCl3_3 and the zigzag antiferromagnetic ground state

The layered honeycomb magnet alpha-RuCl3 has been proposed as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled jeff=1/2 Ru4+ magnetic moments. Here we report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, in contrast with the currently-assumed trigonal 3-layer stacking periodicity. We report electronic band structure calculations for the monoclinic structure, which find support for the applicability of the jeff=1/2 picture once spin orbit coupling and electron correlations are included. We propose that differences in the magnitude of anisotropic exchange along symmetry inequivalent bonds in the monoclinic cell could provide a natural mechanism to explain the spin gap observed in powder inelastic neutron scattering, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as neutron powder diffraction show a single magnetic transition at TN ~ 13K. The analysis of the neutron data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60T show a single transition around 8T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.Comment: 13 pages, 9 figures, published in Physical Review

Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca10_{10}(Pt3_{3}As8_{8})((Fe1−x_{1-x}Ptx_{x})2_{2}As2_{2})5_{5}

We report a high magnetic field study up to 55 T of the nearly optimally doped iron-pnictide superconductor Ca$_{10}$(Pt$_{3}$As$_{8}$) ((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$ (x=0.078(6)) with a Tc 10 K using magnetic torque, tunnel diode oscillator technique and transport measurements. We determine the superconducting phase diagram, revealing an anisotropy of the irreversibility field up to a factor of 10 near Tc and signatures of multiband superconductivity. Unexpectedly, we find a spin-flop like anomaly in magnetic torque at 22 T, when the magnetic field is applied perpendicular to the ab planes, which becomes significantly more pronounced as the temperature is lowered to 0.33 K. As our superconducting sample lies well outside the antiferromagnetic region of the phase diagram, the observed field-induced transition in torque indicates a spin-flop transition not of long-range ordered moments, but of nematic-like antiferromagnetic fluctuations.Comment: Latex, 4 figure

Attractive Stepping Stones Landscapes:Preference for Stone Height Variation Appears to Be Age Independent

An earlier study on the attractiveness of stepping stones configurations revealed that children like variation in stone height better than variation in stone size or gap width. In the present study, we conducted two experiments to examine whether this preference is found also in young and older adults. In Experiment 1, participants stepped freely in a standardized configuration, and three configurations with either height, size or gap width variation. Most interestingly, adults judged playgrounds with variation in stone height as most fun and beautiful, suggesting that the preference for variation in height is indeed age independent. In Experiment 2, we compared the configuration with only height variation with three configurations in which variation in height was combined with variation in stone size or gap width, or both. Although we found no significant differences among the configurations in the older adults, young adults judged the combination of height with size and gap width variation as more fun and esthetically appealing than the configuration with only height variation. The implications of our findings for playground research and designers are discussed.</p

Attractive Stepping Stones Landscapes:Preference for Stone Height Variation Appears to Be Age Independent

An earlier study on the attractiveness of stepping stones configurations revealed that children like variation in stone height better than variation in stone size or gap width. In the present study, we conducted two experiments to examine whether this preference is found also in young and older adults. In Experiment 1, participants stepped freely in a standardized configuration, and three configurations with either height, size or gap width variation. Most interestingly, adults judged playgrounds with variation in stone height as most fun and beautiful, suggesting that the preference for variation in height is indeed age independent. In Experiment 2, we compared the configuration with only height variation with three configurations in which variation in height was combined with variation in stone size or gap width, or both. Although we found no significant differences among the configurations in the older adults, young adults judged the combination of height with size and gap width variation as more fun and esthetically appealing than the configuration with only height variation. The implications of our findings for playground research and designers are discussed.</p

Attractive Stepping Stones Landscapes:Preference for Stone Height Variation Appears to Be Age Independent

An earlier study on the attractiveness of stepping stones configurations revealed that children like variation in stone height better than variation in stone size or gap width. In the present study, we conducted two experiments to examine whether this preference is found also in young and older adults. In Experiment 1, participants stepped freely in a standardized configuration, and three configurations with either height, size or gap width variation. Most interestingly, adults judged playgrounds with variation in stone height as most fun and beautiful, suggesting that the preference for variation in height is indeed age independent. In Experiment 2, we compared the configuration with only height variation with three configurations in which variation in height was combined with variation in stone size or gap width, or both. Although we found no significant differences among the configurations in the older adults, young adults judged the combination of height with size and gap width variation as more fun and esthetically appealing than the configuration with only height variation. The implications of our findings for playground research and designers are discussed.</p

Synthesis and characterisation of end-functionalised poly(N-vinylpyrrolidone) additives by reversible addition–fragmentation transfer polymerisation

We describe herein the synthesis of a series of multi-end functionalized poly(N-vinyl pyrrolidone) (PVP) additives bearing two or three C8F17 fluoroalkyl (CF) groups, designed as additives to modify surface properties. The PVP additives were prepared by reversible addition–fragmentation transfer (RAFT) polymerization, with end functionality imparted via the use of CF functionalized chain transfer agents (CTAs). The resulting PVP additives, when used in modest quantities dispersed in thin films of an unmodified PVP matrix significantly reduce the surface energy, rendering their surfaces more hydrophobic and lipophobic. This is achieved by virtue of the low surface energy of the pendant C8F17 end groups which cause the additive to spontaneously surface segregate during the spin coating process. The resulting thin films have been characterized by static contact angle measurements using dodecane as the contact fluid, and the impact of additive molecular weight, matrix molecular weight, the number of CF groups and additive concentration upon surface properties is reported herein. Significant increases in contact angle were observed with increasing additive concentration, up to a critical aggregation concentration (CAC). Increasing the number of CF groups (from 2 to 3); reducing additive molecular weight or increasing the matrix molecular weight, resulted in increased contact angles and hence surface lipophobicity. Rutherford backscattering (RBS) analysis was performed on films containing varying concentrations of additive, in order to quantitatively measure the near-surface fluorine concentration of these films. The results of these experiments were in excellent agreement with those obtained by contact angle analysis, confirming the surface activity and low surface energy of the additives