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Etude par RMN et MuSR des composés antiferromagnétiques fortement frustrés à géométrie de bicouches kagomé

Abstract : The frustration of antiferromagnetic interactions are responsible for a spin liquid ground state in the Heisenberg kagomé compounds. It is probably described by an RVB state, early proposed by Anderson in 1973 in antiferromagnetic triangular networks and further on cuprates. The macroscopic degeneracy of the low lying singlet states inside the spin gap to the triplet state yield very intersting low-T behaviours. Only few experimental compounds are close to the ideal one today since small perturbations may lift this degenaracy when T->0. An NMR, MuSR and SQUID study has been performed on the S=3/2 kagomé bilayers Ba2Sn2ZnGa10-7pCr7pO22 and SrCr9pGa12-9pO19, considered as archetypes of Heisenberg 2D frustrated magnets. Because of the frustration of the interactions, a transition temperature Tg~2 K is measured only well below the Curie-Weiss temperature. Very close magnetic properties in both systems are found despite different kinds of defects, which underly the intrinsic behavior of the geometry: - the susceptibility decreases below 45 K (NMR). Its analysis shows that the magnetic correlations remain short ranged, at least for T>10 K, despite strong antiferromagnetic interactions (thetaCW~250 K). This maximum is also consistent with the existence of a spin gap; - spin fluctuations are measured down to 30 mK, much lower than Tg using MuSR and suggest a fluctuating state; - this T independent fluctuating state only appears below the spin glass like transition. A phenomenological approach of the muon relaxation is presented for the first time in theses systems and suggests the existence of a RVB state below Tg.
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https://tel.archives-ouvertes.fr/tel-00008532
Contributor : David Bono <>
Submitted on : Monday, February 21, 2005 - 10:23:48 AM
Last modification on : Wednesday, September 16, 2020 - 4:32:01 PM
Long-term archiving on: : Monday, September 20, 2010 - 12:11:42 PM

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David Bono. Etude par RMN et MuSR des composés antiferromagnétiques fortement frustrés à géométrie de bicouches kagomé. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00008532v2⟩

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