Туннельная проводимость и туннельное магнитосопротивление пленок Fe-SiO: корреляция магнитотранспортных и магнитных свойств

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  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 (T) follow the law (T) ~ exp(2(С/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.

Phase shift for total reflection from a bounded dielectric layer

The reflection of horizontally polarized electromagnetic waves from a stratified lossless dielectric region is considered. The region consists of two homogeneous half-spaces separated by a transition zone with a linearly varying permittivity. For angles of incidence sufficiently near grazing, it is shown that the magnitude of the reflection coefficient is unity, but the phase shift on reflection depends on the width of the transition zone in addition to the permittivity gradient. Some numerical results for the phase shift are given and discussed in relation to various limiting situations.