Magnetic and structural properties of (Co) x (SiO 2 ) 1 À x nanocomposite systems have been investigated over a wide range of Co concentrations using small-angle neutron scattering in combination with magnetic, magneto-optic, and magnetotransport characterization. It was found that in the region of structural percolation ðx ¼ 0:46:::0:6Þ, the characteristics of magnetically correlated clusters are several times larger than the structural size of Co granules. Starting from the percolation point, the spatial distribution of magnetic nanoclusters can be described by the surface fractal model. With further growth of cobalt concentration x ! 0.67 the formation of three-dimensional (3D) magnetic domains with typical sizes of 1.5 mm was observed.ß 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Composite materials based on nanoparticles of magnetic metals dispersed in the nonmagnetic matrix are of great interest not only for fundamental study, but also for its possible applications. Physical properties of such composites can be diametrically opposite to the properties of original bulk materials. Composite materials have unique characteristics like giant magnetoresistance, giant tunnel magnetoresistance [1], and the giant anomalous Hall effect [2]. Moreover, the typical granular systems show featured behavior in linear and nonlinear optical and magneto-optical (MO) experiments [3,4]. Nowadays MO properties of granular alloys are studied because of possible application as magneto-active recording media and wide range MO sensors. Recently it was suggested that granular alloys could be used as MO elements in magneto-photon crystals [5]. It has been shown, that magneto-transport and, especially, MO effects are sensitive not only to characteristic dimensions, shape and topology of granules, but also to variations in their magnetic or electronic structure [6]. Analysis of the magnetic interaction of granules and the clusters they form is very important for a correct explanation of the observed properties of granular nanocomposites.
Neutron depolarization studies using pulsed polarized neutrons have been performed to get information on mean magnetization, static magnetization fluctuations and magnetic anisotropy in plate-like ferromagnetic samples. The approach to magnetic saturation of polycrystalline ferromagnets ((Fe50Ni50)96Cr4, and MnZn-ferrit) was studied by analysing the field dependence of depolarization parameters
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