Tunnel Conductivity and Tunnel Magnetoresistance of the Fe-SiO Films: Interplay of the Magnetotransport and Magnetic Properties

The electrical properties of a system of nanogranular amorphous Fe–SiO films with a SiO concentration between 0 and 92 vol % have been investigated. The samples with a low SiO content are characterized by the metal-type conductivity. With an increase in the dielectric content x in the films, the concentration transition from the metal to tunneling conductivity occurs at x ≈ 0.6. At the same concentration, the ferromagnet–superparamagnet transition is observed, which was previously investigated by the magnetic method. The temperature dependences of the electrical resistivity ρ(T) for the compositions corresponding to the dielectric region obey the law ρ(T) ~ exp(2(C/kT)^1/2), which is typical of the tunneling conductivity. The estimation of the metal grain sizes from the tunneling activation energy C has shown good agreement with the sizes obtained previously by analyzing the magnetic properties. In the dielectric region of the compositions, the giant magnetoresistive effect attaining 25% at low temperatures has been obtained.