Absence of Long Range Magnetic Order in the La1.4Sr0.8Ca0.8Mn2O7 Bilayered Manganite

In this work we studied, by means of high-resolution neutron diffraction as a function of temperature, the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite for two different annealing treatments. Out data allowed us to shown, for the first time, the absence of long-range magnetic order in this optimally doped bilayered manganite where the A-site of the structure is doped with equal proportions of different isovalent cations (Ca and Sr). The system, however, presents defined IM transitions which suggest that the transport properties are not linked to the evolution of long-range order and that two dimensional spin ordering in the layers of the perovskite blocks may be sufficient to 'assist' the hole hopping. Possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions.Comment: 24 pages, 7 figure

Sodium Doped LaMnO3 Thin Films: Influence of Substrate and Thickness on Physical Properties

In this paper we report the results about the synthesis and characterization of optimally doped La1-xNaxMnO3 thin films grown onto SrTiO3 (100), NdGaO3 (100) and NdGaO3 (110) for thickness ranging from 11 to 82 nm. The effect of substrate nature and orientation, film thickness and annealing procedure was investigated in order to optimize their magnetoresistance (MR). We obtained very smooth films displaying MR values greater than 70%, near to room temperature.Comment: 31 pages, 9 figures Final version to appear in J. Phys. Chem.

Unexpected effect of Ru-substitution in lightly doped manganites

In this Communication we report about the unexpected effect of ruthenium doping in sodium ligthly-doped manganites. This effect seems to be in contrast with the usual model applied to describe the effect of this magnetic ion into the manganite structure. We propose a possible compensation mechanism which seems also able to describe other peculiar features encountered in these materials.Comment: 3 pages, 2 Figures to appear in ChemCom

Composition and Epigenetic Markers of Heterochromatin in the Aphid Aphis nerii (Hemiptera: Aphididae).

A detailed karyotype analysis of the oleander aphid Aphis nerii focusing on the distribution, molecular composition and epigenetic modifications of heterochromatin was done in order to better understand the structure and evolution of holocentric/holokinetic chromosomes in aphids. The female karyotype (2n = 8) consisted of 3 pairs of autosomes and a pair of X chromosomes that were the longest elements in the karyotype and carried a single, terminally located nucleolar organizer region. Males showed 2n = 7 chromosomes due to the presence of a single X chromosome. Heterochromatin was located in the X chromosomes only and consisted of 4 satellite DNAs that have been identified. A. nerii constitutive heterochromatin was enriched in mono-, di- and tri-methylated H3 histones and HP1 proteins but, interestingly, it lacked DNA methylation that was widespread in euchromatic chromosomal regions. These results suggest that aphid heterochromatin is assembled and condensed without any involvement of DNA methylation

Oxygen content variation and cation doping dependence of (La)1.4(Sr1-yCay)1.6Mn2O7 (y = 0, 0.25, 0.5) bilayered manganites properties

The results of the synthesis and characterization of the optimally doped (La)1.4(Sr1-yCay)1.6Mn2O7 solid solution with y=0, 0.25 and 0.5 are reported. By progressively replacing the Sr with the smaller Ca, while keeping fixed the hole-concentration due to the divalent dopant, the 'size effect' of the cation itself on the structural, transport and magnetic properties of the bilayered manganite has been analysed. Two different annealing treatments of the solid solution, in pure oxygen and in pure argon, allowed also to study the effect of the oxygen content variation. Structure and electronic properties of the samples have been investigated by means of X-ray powder diffraction and X-ray absorption spectroscopy measurements. Magnetoresistivity and static magnetization measurements have been carried out to complete the samples characterization. Oxygen annealing of the solid solution, that showed a limit for about y=0.5, induces an increase of the Mn average valence state and a transition of the crystal structure from tetragonal to orthorhombic while the argon annealing induces an oxygen under-stoichiometry and, in turn, a reduction of the Mn average valence state. Along with the Ca substitution, the Jahn-Teller distortion of the MnO6 octahedra is reduced. This has been directly connected to a general enhancement of the transport properties induced by the Ca-doping. For the same cation composition, oxygen over-stoichiometry leads to higher metal-insulator transition temperatures and lower resistivity values. Curie temperatures (TC) reduce by increasing the Ca-doping. The lower TC for all the annealed samples with respect to the 'as prepared' ones are connected to the strong influence on the magnetic interaction of the point defects due to the oxygen content variation.Comment: 49 pages, 13 figure

PRELIMINARY MAPPING OF GLACIERS AND GLACIAL LANDFORMS OF MOUNT AĞRI DAĞI (ARARAT), EASTERN ANATOLIA - TURKEY

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Chemical Pressure Effect on the Magnetic Order of the La1.4Sr1.6Mn2O7 Bilayered Manganite

In this Communication is it shown the role of Ca-doping in stabilizing the A-type AFM structure of the optimally doped La1.4Sr1.6Mn2O7 bilayered manganite.Comment: 10 pages, 4 figure

Geomorphology of Mount Ararat/Ağri Daği (Ağri Daği Milli Parki, Eastern Anatolia, Turkey)

This paper presents a geomorphological map of Mount Ararat/Ağri Daği in Eastern Anatolia (Turkey). Mount Ararat/Ağri Daği is a volcanic complex covered by a unique ice cap in the Near East. The massif is the result of multiple volcanic phases, and present day landforms are the result of subsequent and overlapping glacial, periglacial, and slope processes. The geomorphological mapping of Mount Ararat/Ağri Daği was firstly performed on the basis of desktop studies, by applying remote-sensing investigations using high-resolution satellite imagery (PLEIADES and SPOT images). A preliminary draft of the map was crosschecked and validated in the field as part of an interdisciplinary campaign carried out in the 2014 summer season. All the collected data suggest that the Mount Ararat/Ağri Daği glaciation played a crucial role in the evolution of the landscape and that even today glaciers are significant features in this area. Currently, ice bodies cover 7.28 km2 and include peculiar glacier types. Among these are three well-developed debris-covered glaciers, flowing down along the flanks of the volcano