6,637 research outputs found
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
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
The role of microRNAs in thyroid carcinomas
Thyroid cancers (TCs) are the most common malignancies of endocrine organs. They originate from cells of different origin within the thyroid gland, which is located at the base of the neck. Several forms of TCs have been classified and great variability is observed in molecular, cellular and clinical features. The most common forms have favorable prognosis but a number of very aggressive TCs, which are characterized by a less differentiated cellular phenotype, have no effective treatment at the moment. While TC causes are not completely understood, many genetic factors involved in their onset have been discovered. In particular, activating mutations of BRAF, RET or RAS genes are known to be specifically associated with TC initiation, progression and outcome. The involvement of microRNAs in thyroid neoplasms has recently changed the paradigm for biomarker discovery in TC, suggesting that these small non-coding RNAs could be used to develop, refine or strengthen strategies for diagnosis and management of TCs. In this review, the importance of microRNA profiling in TC is explored suggesting that these molecules can be included in procedures that can perform better than any known clinical index in the identification of adverse outcomes
Mechanical characterization of sol–gel epoxy-silylatedhyperbranched poly(ethyleneimine) coatings by meansof Depth Sensing Indentation methods
A series of hybrid epoxy-silica coatings were prepared from a synthesized hyperbranched poly(ethyleneimine) with ethoxysilyl groups at the chain ends and diglycidylether of bisphenol A in different proportions. The curing procedure was based in a first sol-gel reaction performed at 80 °C in a humid chamber followed by the anionic homopolymerization of epoxides initiated by 1-methylimidazole in an oven at 180 °C. The prepared coatings were characterized mechanically by means of Depth Sensing Indentation technique. The influence of physical ageing on indentation hardness has been evaluated. The kinetic of the delayed depth recovery has been analyzed using the phenomenological so-called Kohlrausch-Williams-Watts relaxation function. It has been found that silylated hyperbranched poly(ethyleneimine) improves simultaneously the mechanical coating performance and the elastic recovery.Postprint (author's final draft
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
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.
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