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Magnétisme et ordre local des quasicristaux et liquides AlPdMn et AlMn

Abstract : In order to understand the magnetic properties of AlPdMn and AlMn quasicrystals, a closely related crystalline phase, namely the approximant Μ-Al4Mn, was studied. N. M. R. experiments revealed the intrinsic and homogeneous nature of this magnetism. Susceptibility measurements were interpreted within a Kondo model which allowed to evaluate quantitatively the percentage of magnetic Mn atoms and to identify the magnetic site (non icosahedral environment). These results were generalized to quasicrystals. The electronic properties of AlCuFe and AlPdRe quasicrystals were also investigated. N. M. R. experiments showed an unusual relaxation of the nuclear magnetization that was partly interpreted by the presence of a dip in the electronic density of states at the Fermi level, characteristics feature of quasicrystals. Neutron scattering experiments and magnetic susceptibility measurements also allowed getting deeper insight into the magnetic properties and structure of AlPdMn and AlMn liquids, in equilibrium with quasicrystalline and approximant phases. The good agreement, at large momentum transfer values, between the measured structure factors and those calculated from models of liquids containing icosahedral-like clusters, as well as the analysis of the partial pair distribution functions in Al(MnCr) liquid alloys, are in favor of the presence of icosahedral local order in AlMn and AlPdMn liquids. The magnetism of these liquids strongly increases upon melting and goes on increasing in the liquid state with the temperature: a large part of Mn atoms or all of them bear a magnetic moment in the liquid state. An interpretation of these surprising results is discussed in relation with the local order evolution.
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Submitted on : Friday, December 24, 2004 - 1:55:12 PM
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Virginie Simonet. Magnétisme et ordre local des quasicristaux et liquides AlPdMn et AlMn. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 1998. Français. ⟨tel-00007856⟩

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