Tunnel conductivity and tunnel magnetoresistance of Fe–SiO films: correlation between magnetotransport and magnetic properties

The paper presents the results of a study of the electrical properties of a system of nanogranular amorphous Fe–SiO films with a SiO concentration from 0 to 92 Vol.%. For samples with a low SiO content, metallic conductivity takes place. With an increase of the dielectric content, a concentration transition of conduction from the metallic regime to the tunnel regime at a dielectric concentration $x\approx$ 0.6 is observed. At the same concentration, a transition ferromagnet – superparamagnet occurs, which was previously investigated by the magnetic method. For compositions corresponding to the dielectric region, the temperature dependences of the electrical resistance $\rho(T)$ follow the law $\rho(T)\sim\exp(2(C/kT)^{1/2})$, which is typical for the tunnel mechanism of conductivity. Estimation of the sizes of metal granules from the values of the tunneling-activation energy $C$ showed a good agreement with the sizes obtained earlier from the analysis of magnetic properties. In the dielectric range of the compositions, a giant magnetoresistive effect was obtained, reaching 25% at low temperatures.