Concentration dependence of the anomalous Hall effect in Fe/SiO2 granular films below the percolation threshold

The anomalous Hall effect is studied on Fe-x(SiO2)(1-x) nanocomposite films with x < 0.7 in the vicinity of the percolation transition (x(c) approximate to 0.6). It is found that, as the transition is approached from the side of metallic conduction, the Hall angle nonmonotonically varies, passing through a minimum. A qualitative model for describing the concentration dependence of the anomalous Hall effect is proposed. The model is based on that of the conductivity of a two-phase system near the percolation threshold [9, 10]. The anomalous Hall effect is governed by two conduction channels: one of them (a conducting network) is formed by large metal clusters that are separated by narrow dielectric interlayers below the percolation threshold, and the other is represented by the dielectric part of the medium containing Fe grains; in this part of the medium, the anomalous Hall effect occurs through the interference of amplitudes from the tunneling junctions in a set of three grains. It is shown that, at x < x(c), the network may give rise to a "shunting" effect, which makes the effective Hall voltage even less than the Hall voltage of the dielectric component. (C) 2000 MAIK "Nauka / Interperiodica".