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International audience; This paper is devoted to magnetic and structural properties of anisotropicγ-Fe 2 O 3 γ-Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the relevance of basic assumptions of the model for the specimens studied. The experimental results and the related theoretical discussion should be of use to understand magnetic properties of other magnetically textured superparamagnetic systems.

Nous decrivons nos etudes magnetiques et magneto-optiques sur des multicouches Co-Ni/M (M = Pt, Au) preparees par evaporation sous ultra vide. L' anisotropie de surface K s augmente lineairement avec la teneur en Co ce qui verifie le modele a un ion. La teneur relative de Ni permet d'ajuster la temperature de Curie afin de pouvoir utiliser ces materiaux pour l'enregistrement thermomagnetique. La rotation Kerr presente un pic vers 4 eV pour les multicouches a base de Pt, qui se situe vers 2,5 eV pour celles d'or. On discute des resultats.