Magnetoresistance of amorphousMoxGe1−xnear the metal-insulator transition

The magnetoresistance of amorphous ${\mathrm{Mo}}_{\mathrm{x}}$ ${\mathrm{Ge}}_{1\mathrm{-}\mathrm{x}}$ has been measured in samples ranging from metallic to insulating. The positive magnetoresistance found in the metallic samples can be explained by the electron interaction theory. On the other hand, the magnetoresistance of the insulating sample was negative at low magnetic fields and became positive at high fields, which cannot be explained by existing theories. The fractional change in resistivity on applying a magnetic field of 9 T at low temperatures to a range of samples of successively decreasing x was positive, increased monotonically through the metal-insulator transition, and appeared to saturate in the insulating regime.