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Synthèse et caractérisation de pérovskites doubles magnétorésistives dérivées de Sr2FeMoO6

Abstract : This work is devoted to the synthesis and physico-chemical characterization of Sr2FeMoO6, Sr2FexMo2-xO6 (x = 0.9-1.33) and Sr2FeCrxMo1-xO6 (x = 0.1-0.25) double perovskites. For Sr2FeMoO6 the solid state synthesis conditions influence the microstructure of the samples and the Fe/Mo order. Successive sintering treatments with intermediate grindings improve the saturation magnetization (3.8 µB) which became close to the ideal value (4 µB) and the low field magnetoresistance (LFMR) from 1.58 ± 0.14 % to 2.74 ± 0.01 % (T = 300 K, H = 1 kOe) as a consequence of microstructural changes. The effective magnetic moment values depict the presence of mixed valency states: FeII/MoVI and FeIII/MoV. The Sr2FexMo2-xO6 solid solutions (tetragonal symmetry or cubic for x > 1.2) are stable for a larger excess of iron than of molybdenum. The Fe/Mo order diminishes when the difference between x and 1 becomes larger and is stabilizing to an equilibrium value after a high number of sintering treatments for a given x. The Tc arises with x (Fe-Fe couplings stronger than Fe-Mo), but the saturation magnetization is maximum for x = 1. The resistivity enhances with x (delocalized electrons come from molybdenum) presenting thus a stronger dependence of the chemical composition than the microstructure. The magnetoresistance is maximum for x = 1 ; for x = 1.33 the composition ceases to be a half-metal. For Sr2FeCrxMo1-xO6 solid solutions, the increase of chromium content determines the diminution of octahedral sites cationic order and thus a decrease of Tc, magnetization and magnetoresistance.
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Submitted on : Tuesday, July 5, 2005 - 6:21:56 PM
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Ciprian Bogdan Jurca. Synthèse et caractérisation de pérovskites doubles magnétorésistives dérivées de Sr2FeMoO6. Matériaux. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00009675⟩

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