Formation of the magnetic fractal structure in Co-SiO_2 granular nanocomposite system at percolation threshold

摘要

Magnetic and structural properties of (Co)_x(SiO_2)_(1-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 magneto-transport characterization. It was found that in the region of structural percolation (x=0.46...0.6), 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 1.5μm was observed.