Relation entre magnétisme et supraconductivité
dans quelques matériaux SHTc de type Y123

Abstract : The aim of this work was to look for some answers to the special non-superconducting
behaviour of the praseodymium 1212 cuprate PrBa2Cu3O7 (Pr123), in contrast to the other
compounds of the same series which are all superconductors.
After an exhaustive bibliography on the subject, the remaining unsolved questions and the
contradictions found in the literature are reviewed.
A great number of PrxY1-xBa2Cu3Oy powder and sintered samples have been elaborated
with different composition (x = 0 to 1) and oxygenation state (y = 6 to7). They have been
carefully checked for crystallographic structure and morphology, oxygen content and phase
purity. Their magnetic and thermal behaviour, together with samples from other teams, has
been studied by precise susceptibility, magnetisation, thermal expansion and specific heat
measurements. Careful analyses of the magnetic results allow us to separate the stoechiometry
and Pr/Ba substitution effects from those coming only from the oxygen content. In fact, the
magnetic behaviour of the Pr3+ ions is not much affected by the substitutions while the oxygen
has a strong effect on the exchange interactions strength. Crystal field calculations have been
made and they confirm the little effect on the Pr moment, but also, they can explain several
features that have been often misinterpreted as for example the constant term of the
susceptibility
Pure Y123 and other rare earth compounds, like Dy123 and Ho123, have been also
measured in different oxygenation states (y~ 6, 6.5 and 7). Their study seem to evidence a close
relation between the amount of oxygen's, and their degree of disorder, and the magnetic
behaviour of copper in the CuO2 planes but also especially in the chains CuO. The later are
most probably at the origin of the susceptibility tails and weak ferromagnetism observed at low
temperatures as soon as the oxygen number is not close to 7
This work brings some new insight into the behaviour of this series of compounds and
gives some new directions for the understanding of the interdependence of magnetism and
superconductivity in the SHTc's
Document type :
Theses
Condensed Matter [cond-mat]. Université Badji Mokhtar - Annaba, 2006. French


https://tel.archives-ouvertes.fr/tel-00119520
Contributor : Aïcha Harat <>
Submitted on : Monday, December 11, 2006 - 10:09:50 AM
Last modification on : Monday, December 11, 2006 - 12:01:13 PM

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Aïcha Harat. Relation entre magnétisme et supraconductivité
dans quelques matériaux SHTc de type Y123. Condensed Matter [cond-mat]. Université Badji Mokhtar - Annaba, 2006. French. <tel-00119520>

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