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.. Le-modèle-de-heisenberg-antiferromagnétique-sur-le-réseau-kagomé, 10 1.1 Présentation du modèle

D. Caractérisation-du and .. Bilan-provisoire, 14 a) Paramètre d'ordre et forme du spectre, 14 b) Le cas du réseau, p.17

S. Lesétatslesétats, 21 a) Non-orthogonalité 21 b), 22 c) Caractère variationnel de la base, p.24

T. Le-modèle, 24 a) Présentation du modèle 24 b) Termes engendrés par les liens vacants, p.26

.. Utilisation-numérique-des-symétries, 30 a) 30 b) Les configurations représentatives 30 c) Réduction du nombre des représentatifs, p.31

O. Le-cas, 32 a) Détermination de µ s 32 b) Calcul d'´ eléments de matrices, p.32

.. Généralisation-au-cas-non-orthogonal, 33 a) Détermination de µ s, p.33

S. Description, . Du-modèle-de-heisenberg-sur-le-réseau-kagomé...., and .. Le-hamiltonien-effectif, 35 4.1 L'approche de champ moyen sur le modèle trimérisé, 35 b) L'approche de champ moyen . . . . . . . . . . . . . . . . . 37

T. Le-modèle, 37 a) La limite ? = 0 37 b) La limite ? = 0 ? ´ etats excités 39 c) Trimérisation forte (? 1) 40 d) Spectre SRRVB / Spectre exact, 42 e) Conclusion, p.42

I. Le-modèle, 43 a) Caractéristiques du spectre 43 b) Comptage desétatsdesétats, p.45

.. Le-hamiltonien-effectif-de-bassé-energie and H. Le-fondamental-de, 59 b) Excitations de H({T i = 1/2) 60 c) Fondamental de H({T i =i 0 = 1, p.60

T. Principaux-résultats, 68 a) L'´ echec du modèle non frustré, p.68

C. Présentation-des, 80 a) Structure cristallographique et possibilités d'´ echange . . . 80 b) Susceptibilité magnétique, 81 c) Résonance magnétique nucléaire . . . . . . . . . . . . . . . 82

L. Interprétation-de, 86 a) Forme des susceptibilités expérimentales