Conductivity and anomalous Hall effect in film magnetic nanocomposites based on nonstoichiometric oxides

Abstract

The transport properties of film nanocomposites (Co₄₀Fe₄₀B₂₀)_x(AlO_y)_{100 − x} and (Co₈₄Nb₁₄Ta₂)_x(AlO_y)_{100 − x} based on AlO_y oxide (y ~ 1), containing a ferromagnetic metal, are studied in the region of the metal–insulator transition (57 > x > 47 at %). It is found that at x > 49 at %, the conductivity of nanocomposites is well described by a logarithmic law of σ(T) = a + b ln T, which can be explained by the peculiarities of the Coulomb interaction in nanogranular systems with metallic conductivity near the metal—insulator transition. It is shown that parameter b is determined by the characteristic size of the percolation cluster cell, which in nanocomposites of both types happen to be the same (~8 nm) and correlates well with the results of electron microscopy studies. The temperature dependence of the anomalous Hall effect at the logarithmic dependence of conductivity is studied for the first time. In the immediate vicinity of the transition, a power-law scaling between the anomalous Hall resistance and longitudinal resistance ρ_H^a ∝ ρ^0.4, is detected, which can be explained by the suppression of its own mechanism of the anomalous Hall effect under the strong scattering of charge carriers.