G. Sur, L. C. Aux, and . Fig, 11 ? a) Spectre de temps de vol d'agrégats de cobalt. b) Zoom et indexation des premiers pics du spectre complet en a)

G. Sur, L. C. Propriétés-magnétiques-d-'un-agrégat, . De, . Unique, . Modèle et al., 3 ? Surfaces d'énergies d'anisotropie de surface et magnéto-cristalline d'un agrégat de huit couches possédant 0

A. De, . Posés, and . Coo, Pour l'autre moitié des agrégats, appartenant tous au même micro-SQUID D, on constate que les directions du champ de décalage ne sont pas colinéaires au champ H FC (?40°< ? E < 0°) De plus, le signe de ce décalage est positif comme pour l'agrégat D-1. Comme nous l

. Si, 30, la direction du champ de décalage est aléatoire, selon la rugosité et l'anisotropie locale de la couche AF, bien que pour un même micro-SQUID presque tous les champs de décalages soient positifs

. Les-champs-d, échange mesurés dans cette géométrie ? agrégats/CoO ? sont très faibles (en moyenne 15 Oe) Cependant, ils ne sont pas en contradiction avec les mesures macroscopiques si 4. PROPRIÉTÉS MAGNÉTIQUES D'UN AGRÉGAT DE COBALT UNIQUE sont mises en évidence par des flèches pleines lorsqu'il s'agit de la direction réelle, et en tirets lorsqu'il s'agit d'une projection dans le plan de mesure XY (µSQ)

. Dans-les-deux-représentations, nous avons reporté les axes d'anisotropie magnétique (EA) et d'anisotropie d'échange (HB), ainsi que la procédure appliquée lors du refroidissement de l'échantillon (ZFC ou FC) Dans le cas FC, nous avons aussi indiqué par une flèche la direction

. La-forme-de, on mesure est symétrique arrondie et décalée. D'après la règle n°3 (en fin de section 4.5), cela signifie que soit le champ de décalage est dans le plan de mesure et l'axe d'anisotropie de l'agrégat est en dehors de ce plan (hypothèse 1)

7. Anisotropie-d-'échange-d-'un-agrégat, . De, . Oxydé, and . Fig, 36 ? Mesures des champs de retournement de l'agrégat E-1. Le champ H FC est appliqué le long de l'axe X positif

P. Magnétiques-d-'un-agrégat, . De, . Unique, and . Fig, 39 ? Mesures des champs de retournement de l'agrégat E-1. Le champ H FC est appliqué le long de l'axe Y négatif (FC5)

P. Magnétiques-d-'un-agrégat, . De, and . Unique-enfin, en ce qui concerne l'interprétation des résultats de la procédure ZFC, on a le choix entre deux hypothèses. Dans l'hypothèse 1 le champ de décalage est dans le plan de mesure et l'axe d'anisotropie de la particule en dehors de ce plan. Le fait que le champ d'échange et la direction d'anisotropie magnétique soient les mêmes que pour les procédures FC suivantes est un argument en faveur de cette hypothèse. Par contre le champ d'anisotropie est plus faible que pour toutes les autres mesures. Cette dernière remarque nous incite plutôt à choisir la seconde hypothèse

P. Dans-ce-cas, . Magnétiques-d-'un-agrégat, . De, . Unique, and . Fig, astroïde n'est pas symétrique, cela signifie d'après la règle n°2 (fin de la section 4.5), que le champ de décalage possède une composante perpendiculaire au plan de mesure. On constate que l'ajustement de cette astroïde avec le modèle de Meiklejohn et Bean n'est pas parfait. Cela est dû au fait que l'on ne tient pas compte des termes d'anisotropie 4

P. Magnétiques-d-'un-agrégat, . De, . Unique, and . Fig, 45 ? Mesures des champs de retournement de l'agrégat E-2. Le champ H FC est appliqué le long de l'axe Y positif (FC4)

. Dans-le-plan-de-mesure, lorsque le champ H FC est appliqué selon l'axe X le signe de la projection du champ de décalage est négatif, lorsque H FC est appliqué selon l'axe Y , il est positif. Nous avons attribué cette différence à l'amplitude du champ H FC qui est différente selon X

. La-forme-de-l, astroïde de l'agrégat E-4 est très aplatie, ce qui indique une anisotropie fortement uniaxiale

. Enfin, agrégat F-1 est majoritairement d'anisotropie cubique. L'astroïde mesurée n'est pas complète. Elle ne représente qu'une partie de la distribution des champs de retournement à 2D

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