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J. Fontcuberta J. Jurado X. Obradors M. V. Cabañas M. Vallet J. M. Gonzalez-Calbet 《Zeitschrift für Physik B Condensed Matter》1992,87(1):21-28
This paper reports a detailed study of the electrical transport properties of good quality superconducting Y0.5Sm0.5Ba2Cu3O7 ceramic samples. Analyses of the dependence of resistance on temperature, the relations current-voltage and the magnetoresistance allows to identify:a) the mean field critical temperature (T
CO
=93.73±0.01 K);b) a power law behaviorVI
atT
CO
. The exponent jumps abruptly from 1 to 3, at a certain temperatureT
C
=93.276±0.005 K;c) an exponential inverse root-square temperature dependence of the resistivity in theT
C–T
CO
temperature range. These features, typically observed when topological excitations sets in two dimensional systems, can also be interpreted as a signature of a percolation process and a transition towards intergranular phase coherence. We analyze and discuss the relevance of both models to account for the experimental data. 相似文献
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A. Isalgué A. Labarta J. Tejada X. Obradors 《Applied Physics A: Materials Science & Processing》1986,39(3):221-225
In the scope of the mean field approximation the nine nearest neighbour exchange interactions existing among the ferric ions in BaFe12O19 hexagonal ferrite have been determined from the experimental sublattice magnetizations. It is shown that these exchange interactions are well explained by means of the superexchange theory. It is also concluded that some direct exchange interaction does exist among the octahedral 4f
VI ions. The calculated magnetization, paramagnetic susceptibility, and Curie temperature are in good agreement with the corresponding experimental values. The stability of the collinear Gorter-type magnetic structure of BaFe12O19 is discussed as well. 相似文献
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J. P. Mignot A. Isalgué X. Obradors J. C. Joubert J. Tejada 《Hyperfine Interactions》1986,28(1-4):565-568
The temperature dependence of the hyperfine fields corresponding to ferric ions in the different sublattices of BaLiFe17O27 W-type hexagonal ferrite has been measured. A mean field analysis of these sublattice magnetizations has been done and a set of nearest neighbour isotropic exchange interactions has been obtained. The relative strenght of these fitted exchange values is in accordance with superexchange theory 相似文献
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Hichem Eloussifi Jordi Farjas Pere Roura Jaume Camps Mohamed Dammak Susagna Ricart Teresa Puig Xavier Obradors 《Journal of Thermal Analysis and Calorimetry》2012,108(2):589-596
A detailed analysis of the thermal decomposition of yttrium trifluoroacetate under different atmospheres is presented. Thermogravimetry,
differential thermal analysis, and evolved gas analysis have been used for this in situ analysis. Solid residues at different
stages have been characterized by means of X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy,
and scanning electron microscopy. The first decomposition stage (310 °C) is exothermic and involves the complete removal of
carbon (organic part) and the formation of yttrium fluoride. This process is characterized by a fast mass loss rate. Afterwards,
yttria (Y2O3) is formed at 1200 °C through a slow process controlled by the out diffusion of fluorine that involves the formation of yttrium
oxyfluoride as an intermediate. The evolution of the mass during the decomposition and the structure of the yttria particles
is not affected by the presence of oxygen or water. However, when the oxygen (water) partial pressure is as low as 0.02% (<0.002%),
the kinetics and final particle structure are strongly affected. 相似文献
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The dynamics of the bipyramidal 4e–Fe ions in the M-type hexagonal ferrite La0.7Na0.3Fe12O19 single crystal, is investigated by using Mössbauer spectroscopy. We show that a photon self-interference phenomenon can be used to explain the available experimental data. From this model we have deduced the jumping distance of the Fe(4e) ions. This model can also be succesfully used to investigate the existing data on the isomorphous CaAl11FeO19 and BaFe12O19 oxides. In all cases, the calculated jumping distances are in a excellent agreement with X-ray diffraction results. For CaAl11FeO19 and BaFe12O19 we have deduced the thermal dependence of the jumping distance. Any evidence of an atomic freezing is not found in the temperature range 80–300 K. 相似文献
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