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51.
S. Hébert A. Maignan V. Hardy C. Martin M. Hervieu B. Raveau R. Mahendiran P. Schiffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):419-424
The low temperature magnetic and transport properties of the Pr0.5Ca0.5Mn1-xNixO3 manganites ( 0≤
x
≤0.1) have been investigated. The presence of Ni hinders the charge and orbital ordering observed in Pr0.5Ca0.5MnO3 and favors the creation of ferromagnetic regions, leading to phase separation. The ferromagnetic fractions induced by the
Ni substitution have been estimated from magnetization measurements, they are large and reach 40% for 4% of Ni. Steps are
observed in the M
(
H
) and ρ(
H
) curves of all the samples at T
< 5 K. They are similar to the steps observed in Pr0.5Ca0.5Mn1-xMxO3, where M is a non magnetic cation (Mg2+, Ga3+,...), and for which the ferromagnetic fractions are very small (less than 2%), however, their appearance is restricted to
lower temperatures (T
< 5 K) with Ni dopant than with non magnetic cations. This study shows that steps can be observed in a wide range of phase-separated
systems, even when the ferromagnetic fraction is very large.
Received 5 April 2002 / Received in final form 8 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: antoine.maignan@ismra.fr 相似文献
52.
J.-M.?Le?CorreEmail author E.?Hervieu M.?Ishii J.-M.?Delhaye 《Experiments in fluids》2003,35(5):448-458
Accurate measurements of local time-averaged two-phase flow parameters is of fundamental importance for the evaluation of two-phase flow models as well as for the development of closure relations used in the two-fluid model. For cross-calibration purposes, we compared the measurements of local-time-averaged two-phase flow parameters using a four-sensor conductivity probe developed by the TRSL (Thermal-hydraulics and Reactor Safety Laboratory) at Purdue University, and a four-sensor optical probe developed by the CEA (French Atomic Energy Commission). A system coupling methodology was also performed in order to isolate the effects of each instrumentation's components, i.e., probe, acquisition, thresholding, and processing effects. Experimental results have shown a reasonable agreement in the local void fraction, local bubble velocity, and local interfacial area concentration measurements comparisons. However, it is shown that particular attention must be given to the sensor probe design in order to get accurate measurements. 相似文献
53.
A. Sundaresan J.L. Tholence A. Maignan C. Martin M. Hervieu B. Raveau E. Suard 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):431-438
Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized
electron doped Sr1-xCe
x
MnO3 (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural
transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering () which stabilizes a chain like (C-type) antiferromagnetic ground state with . The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the d
x2-y2 symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance
appears for . Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at
low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped
manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size
may be responsible for the absence of double exchange ferromagnetism and CMR effect.
Received 10 September 1999 相似文献
54.
Maryvonne Spiesser 《Historia Mathematica》2000,27(4):155
The Compendy de la praticque des nombres (1471) is one of a number of commercial arithmetics produced in southern France during the medieval period. Its interest and originality rest in its treatment of problem-solving. The author of the text limited his treatment to an in-depth analysis of only a few types of problems, not treating particular cases but rather emphasizing general methods. The sources from which he drew were very close to the Liber abbaci of Leonardo Fibonacci and many of them were new to the southern French arithmetic tradition. Thus, the Compendy sheds new light on the transmission of arithmetic thought into Europe. Copyright 2000 Academic Press.Le Compendy de la praticque des nombres (1471) est un traité qui appartient au groupe des arithmétiques commerciales du Sud de la France. L'intérêt et l'originalité du texte résident dans la partie consacrée à la résolution de problèmes. L'auteur sélectionne quelques types de problèmes seulement, auxquels il consacre une longue étude, délaissant les cas particuliers pour privilégier les méthodes. Ce faisant, il utilise de nouvelles sources, proches du “Liber abbaci” de Léonard de Pise, étrangères aux autres arithmétiques françaises de la même famille. Le Compendy nous apporte ainsi un éclairage nouveau sur la transmission de l'algorisme. Copyright 2000 Academic Press.MSC subject classifications: 01A35; 01A40. 相似文献
55.
M. Hervieu A. Barnabé C. Martin A. Maignan F. Damay B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):31-41
Charge ordering phenomena in the manganites Ca1-xSmxMnO3 have been studied for , using electron diffraction and lattice imaging, completed by magnetic and transport measurements. Three domains can be distinguished,
depending on the nature of the structural transitions with temperature. For , the structural transition from a pseudo-tetragonal to a monoclinic form, with decreasing temperature, coincides with the
competition between ferromagnetism and antiferromagnetism that is characterized by the temperature Tpeak on the M
(
T
) curves; short-range charge ordering is observed for manganites. For the second domain, , a structural transition from an orthorhombic to a long-range charge ordered state is clearly observed with decreasing temperature.
The corresponding temperature TCO coincides with the temperature Tpeak deduced from magnetic measurements. This long range charge ordering, which appears along a, is either commensurate or incommensurate depending on the x value, with a modulation vector, q being close to x. These modulated superstructures correspond to a stacking of single Mn3+ stripes with multiple Mn4+ stripes along a, either in a commensurate or in an incommensurate manner. The third domain , is characterized by a transition to a charge ordered state with commensurate superstructure at low temperature. The latter
can be described as a “partially” charge ordered state in which single “Mn3+” stripes alternate with mixed “Mn3+/Mn4+” stripes.
Received 17 June 1998 相似文献
56.
M. Hervieu C. Martin A. Maignan G. Van Tendeloo B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):397-408
The structural transitions that appear in the manganites Ca1-xThxMnO3
versus temperature are studied in connection with their magnetic and transport properties, and compared to those of the Ca1-xLnxMnO3 manganites. An orthorhombic to monoclinic transition is observed for low x values (;this structural distortion, also observed for Ln-doped oxides, is related to the magnetoresistance properties. For higher
x values (), modulated commensurate and incommensurate phases are obtained at low temperature, with , b
=2
a
p and , which are related to Mn3+/Mn4+ charge ordering (CO) phenomena. T values, determined from electron diffraction, are in agreement with those determined from the M
(
T
) curves. The low temperature electron microscopy shows that the CO in those oxides is more complex than in Ln-doped manganites.
In particular, the destabilisation of CO and consequently of the antiferromagnetic interactions is evidenced as the thorium
content increases which may explain the appearance of a spin-glass like behavior for higher x values not seen for Ca1-xSmxMnO3 phases .
Received 2 November 1998 相似文献
57.
58.
59.
60.
Maryvonne Maheo 《Discrete Mathematics》1980,29(1):39-46
In this paper, we prove that the n-cube is graceful, thus answering a conjecture of J.-C. Bermond and Gangopadhyay and Rao Hebbare. To do that, we introduce a special kind of graceful numbering, particular case of α-valuation, called strongly graceful and we prove that if a graph G is strongly graceful, G + K2 is also strongly graceful. 相似文献