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Etude par RMN de la susceptibilité et des effets de dilution dans le composé magnétique géométriquement frustré SrCr9pGa12-9pO19

Abstract : The archetype of geometrically frustrated compounds SrCr_(9p)Ga_(12-9p)O_(19) is a kagomé bi-layer of Heisenberg Cr3+ ions (S=3/2) with antiferromagnetic interactions. We present an extensive gallium NMR study over a broad concentration of Cr ions (0.72 < p< 0.95). This allows us to probe locally the susceptibility of the kagomé bi-layer and separate the intrinsic properties due to the geometric frustration from those related to the site dilution. Our major findings are: 1) The intrinsic kagomé bi-layer susceptibility exhibits a maximum in temperature at 40-50 K which we show here to be robust to a dilution as high as 20%. The maximum reveals the development of short range antiferromagnetic correlations. 2) At low temperature, a highly dynamical state induces a strong wipe-out of the NMR intensity, regardless of dilution. 3) The low-temperature upturn of the macroscopic susceptibility is associated to paramagnetic defects which stem from the dilution of the kagome bi-layer. The low-temperature analysis of the p=0.95 NMR lineshape coupled with a more accurate determination of the nuclear hamiltonian at high temperature, allows us to discuss in detail the defects nature. Our analysis suggests that the defect can be associated with a staggered spin-response to the vacancies on the kagomé bi-layer. This, altogether with the maximum in the kagomé bi-layer susceptibility, is very similar to what is observed in most low-dimensional antiferromagnetic correlated systems even with a short spin-spin correlation length. 4) The spin glass-like freezing observed between 2 and 4 K is not driven by the dilution-induced defects.
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Submitted on : Tuesday, December 14, 2004 - 1:00:56 PM
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  • HAL Id : tel-00002395, version 2



Laurent Limot. Etude par RMN de la susceptibilité et des effets de dilution dans le composé magnétique géométriquement frustré SrCr9pGa12-9pO19. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2000. Français. ⟨tel-00002395v2⟩



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