We studied both the resistivity and the Hall resistivity of cosputtered granular Ni–SiO2 films with the metal volume fraction x in the range of 0.5–1.0. Near the metal-insulator transition, or x of about 0.53–0.61, the saturated value of the Hall resistivity was up to 2×10−4 Ω cm. This value is almost 4 orders of magnitude greater than that of pure nickel. Both the resistivity and the Hall resistivity varied weakly with temperature, throughout the range of 5–300 K. We suggest that the percolating ferromagnetic granular metal films can be an alternative candidate material for high sensitivity Hall sensors.

We have used magnetotransport measurements to determine the phase diagram of (TMTSF>2C104 from 0.5 to 10 K in magnetic fields to 30 T. This organic metal becomes a spin-density-wave semimetal as temperature is reduced in a magnetic field greater than a threshold field H c (T=0) -3 T. The critical temperature T C (H) increases with field in agreement with present theories, and reaches a maximum of 5.6 K at 18 T. Above this field, however, T C (H) decreases, extrapolating to zero temperature at 17 T. This reentrant phase diagram is not present in any theoretical model.

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