| The electrical properties of sputtered $rm Nisb{x}(SiOsb2)sb{100-x}$ granular metal films with x in the range 63 to 90 have been studied. The temperature dependence of the resistivity of films with a thickness of approximately 1500 A has been obtained between room temperature and 10 K utilizing a helium closed-cycle refrigerator, with data down to 1.3 K being obtained in a purpose-built pumped liquid $sp4$He cryostat. The same cryostat was used to study the transverse magnetoresistivity in fields up to 6 T at temperatures between 20 K and 1.5 K, with the resistivity being measured by a high resolution ratio-transformer bridge, constructed specifically for this work.;The temperature dependence of the resistivity in films with x $<$ 70 (insulating regime) was found to be of the form $$rho = rhosb0 exp left({Tsb0over T}right)sp{0.5}$$for temperatures above approximately 10 K, with a crossover to a weaker temperature dependence at lower temperatures. Comparison of the experimental data with the predictions of the theory of variable range hopping in a Coulomb gap, although in qualitative agreement with the observations, yields physically unacceptable values of the optimum hop distance. In the metallic regime (x $geq$ 70), the resistivity is found to pass through a minimum as the temperature is reduced, before increasing logarithmically as the temperature is reduced further. Such behavior is predicted by the quantum interference theories of weak localization and electron-electron interactions in two dimensions. However, these films are expected to be three-dimensional, and dimensionality studies through variation of the film thickness between 100 A and 2500 A, at a composition of approximately 85 atomic weight per cent Ni, confirm this.;The transverse magnetoresistance of 1500 A films in both regimes is negative, and is larger than can be explained by the usual ferromagnetic magnetoresistance of nickel. In the insulating regime, the resistivity passes through a minimum as the applied field strength is increased. In the metallic regime the resistivity decreases until saturating in fields of less than 1T, and this magnetoresistance is only weakly temperature dependent. It is shown that the predictions of three-dimensional weak localization, although in qualitative agreement with the experimental observations in weak fields, do not provide a satisfactory explanation of the effect. |
