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We present results of an experimental study of magnetoresistance (MR) in insulating NbSi amorphous alloys sample showing Variable Range Hopping (VRH) conductivity. The MR is found to be negative in a wide range of low temperature (4.2-20 K) and in the range of moderate magnetic fields (0-4 T). We made tentative analysis using three theoretical models which are the model of quantum interference, the model of Zeeman effect and the model of localized magnetic moment

On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures <i>T</i> on the electrical transport in amorphous silicon-nickel alloys a-Si_1-yNi_y:H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with <i>T</i>^-1/2. This behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For <i>T</i> higher than a critical value of temperature <i>T</i>_C, we obtained the Mott Variable Range Hopping regime with <i>T</i>^-1/4, indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical temperature <i>T</i>_C decreases with nickel content in the alloys

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