Magnetic field induced insulator to metal transition in amorphous-GdxSi1-x

We have measured the electrical resistance and magnetoresistance near the m etal-insulator transition in films of the amorphous alloys GdxSi1-x and YxS i1-x (x similar to 0.14 - 0.15) for 0.1 K < T < 20 K in an applied magnetic field 0 kOe < H < 105 kOe. In a low magnetic field, a-GdxSi1-x is an insul ator and the conductivity approximately follows the expected behavior for v ariable range hopping. With increasing field H the conductivity of a-GdxSi1 -x increases by similar to 3 orders of magnitude at low T, crosses through an insulator to metal transition and approaches the conductivity of a-YxSi1 -x indicating that the effect of the magnetic Gd impurities on transport is dimished by the application of a magnetic field. The low-temperature condu ctivity on the metallic side of the transition scales approximately linearl y with the applied magnetic field, indicating that the critical exponent mu approximate to 1. (C) 2000 Elsevier Science Ltd. All rights reserved.